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Living With a Heat Pump Water Heater

My New Rheem Performance Platinum Heat Pump Water Heater

It was two years ago this week we had the nasty old fossil gas natural draft water heater removed.   (That’s it in the photo below.)  Outside of running a gasoline powered generator inside a house, this kind of water heater is probably the number one source of carbon monoxide in homes.  Yes, the hot water is cheap, but how much is your health worth?  So my replacement for this fossil was a heat pump water heater (HPWH).  It’s a Rheem Performance Platinum, and I love it!

Gas natural draft water heater, replaced by a heat pump water heater
Gas natural draft water heater, replaced by a heat pump water heater

Choosing a heat pump water heater

I am not an expert in heat pump water heaters, and I don’t know the range and availability of products all that well.  But I have friends who keep up with that stuff, so I asked one of them.  John Semmelhack of Think Little is a big proponent of all-electric homes, and he recommended the Rheem model that I ended up buying.  Manufacturers are always changing their models, though, so my generation 4 has evolved into the generation 5 model (I think).  Also, when you’re searching for information, Rheem uses the term “hybrid water heater” because its main source of heat is the heat pump, but it also has built-in electric resistance heating.

One of the choices you have to make when buying any water heater is size.  I sprang for the 80 gallon model for one simple reason.  If I’m going to use a heat pump water heater, I want it to use the heat pump all the time.  I don’t want to use the electric resistance heating element at all unless the heat pump fails.  The smaller the tank you buy, the more likely it is you’ll have to use some electric resistance heating.

The bigger tank has the other advantage of having more hot water available.  My 80 gallon model has an 89 gallon first-hour rating.  Did I go overboard?  Yeah, probably.  I do that sometimes.  This weekend we’ll get to put it to the test as we’re having family in town for my 120th birthday party.*  That larger tank should come in handy.

The Rheem app

The Rheem HPWH connects to wifi and has a nice app for your smartphone.  The screenshot below shows the main screen for the water heater, with the basic info about the generation (4), water temperature setting (120° F), mode (HP only), and links to other data (schedules, usage report, and wifi settings, to the left of the temperature).

And it has one annoying notice I wish Rheem would change.  That green bar is ALWAYS there for me because I’ve set the mode to heat pump only.  Their so-called Energy Saving mode would actually use more energy because it would use electric resistance heat sometimes.

The Rheem app
The Rheem app

Monitoring energy use

We fired up (so to speak) our new water heater on 14 September 2019, so we just passed the two-year mark.  How much electricity have we used in that time?  The chart below shows our first full year of data.  The total was 486 kilowatt-hours (kWh).  The lowest month was August at 23.75 kWh, and the highest was December at 68.6 kWh.

Energy use for each month of the year 2020 for my Rheem heat pump water heater
Energy use for each month of the year 2020 for my Rheem heat pump water heater

Notice the pattern?  Water heating energy use is low in summer and high in winter.  The main reason for that is the entering water temperature.  As everything cools down in the fall, the municipal water supply cools down, too.  That means it takes more heat pumped into the water to raise the temperature to 120° F.

A second reason is that we use more hot water in winter, although I actually haven’t measured that yet.  Next year, however, I’m going to set up flow meters and temperature sensors on my all-new hot water plumbing when I remodel my basement.  Then I’ll have the data to prove it, at least in my household.  Those data will also tell me how many kilowatt-hours it takes to get a gallon of hot water, by each month of the year and averaged over the whole year.

A third reason we use more energy in the winter is that the HPWH pulls heat out of the air, and our basement air is cooler in winter.  In my case, we currently don’t heat or use the basement much so it’s not a big deal.  In cold climates, it can be a big deal.

Rheem HPWH energy use by month for 2021 compared to energy use for 2020
Rheem HPWH energy use by month for 2021 compared to energy use for 2020

Another nice feature of the Rheem app is that it can show your current usage compared to usage for the previous period.  The chart above shows it by month for 2021 so far compared to the corresponding months in 2020.  It also does daily by hour, weekly by day, and monthly by day.

Our annual consumption

Since it’s been just a couple of days over two years since I started up the heat pump water heater, I can tell you how much energy we’ve used in that time and how much it has cost us.  From 14 September 2019 to 14 September 2021, we used 1,002 kWh.  I also track our electricity use in a spreadsheet (doesn’t everybody?), and over that period, our average rate from Georgia Power has been almost exactly $0.10 per kilowatt-hour (excluding taxes and fees).  So we’ve paid just a bit (two bits actually) over $100 for two years’ worth of hot water.

The EnergyGuide shows $161 for the annual estimated energy cost for our heat pump water heater
The EnergyGuide shows $161 for the annual estimated energy cost for our heat pump water heater

How does that compare to our old fossil gas water heater, you ask?  We lived with it for less than three months, so I don’t have full data.  But based on the little that I do have, it looks like the gas water heater would have cost us close to the same amount (again, excluding taxes and fees).  So, there’s no direct economic benefit to switching from a gas water heater to a heat pump water heater…when I look at the cost based on rates only.

I paid $34.55 per month in natural gas fees even when I didn't use any gas

I had already made the decision to get rid of our gas furnace, however, and that meant our only remaining gas appliance would be the water heater.  At about $38 per month (screenshot above), the fees just to have gas would make the heat pump water heater a big money saver.  Based on a marginal cost of $1,200, the extra $450 per year in gas fees ($38 x 12) would give me a simple payback of about 3.5 years!

If I had replaced an electric resistance water heater, however, we still would have saved money; just not as much.  The efficiency of water heaters is rated by something called the Uniform Energy Factor (UEF).  Higher numbers are better, and my HPWH has a UEF of 3.7.  (You can see it on the EnergyGuide above.)  A standard electric water heater has a UEF of about 0.9, making my HPWH about 4.1 times as efficient.

Instead of 501 kWh per year, I would have used about 2,000 kWh per year with an electric resistance water heater.  At $0.10 per kWh, I would have saved about $150 per year on water heating.  With a simple payback of about 10 years in this case, it wouldn’t be hard to justify this purchase for economic reasons, assuming a 15 or 20 year lifetime and minimal maintenance costs.

Noise, ducting, and filtration

One thing people have complained about with some heat pump water heaters is that they’re too noisy inside the house.  Some probably are, so I measured mine using the NIOSH SLM app on my phone.  Here are my results:

  • 53 dBA — one foot straight out from the exhaust port
  • 48 dBA — one foot to the side of the exhaust port
  • 46 dBA — five feet away, at the mechanical room door
  • 37 dBA — four feet to the side of the mechanical room door

That’s pretty quiet.  For reference, here are some other noise levels on this scale:

  • 60 dBA — normal conversation
  • 50 dBA — rainfall
  • 40 dBA — refrigerator hum
  • 30 dBA — soft whisper

Another nice feature of the Rheem model I bought is that it allows for the intake air and exhaust air to be ducted.  You can see the exhaust port in the lead photo.  It’s to the right of the digital display screen.  My water heater is in the basement, so I could run a duct up to the encapsulated attic to bring in warmer intake air and make the heat pump more efficient.  But it would be more trouble than it’s worth in my case.

I will need to run a short duct to the mechanical room wall, though.  After I remodel the basement and put a door on the mechanical room, the HPWH won’t have much air in that space so the duct will bring in air from the rest of the basement.

Even if you don’t duct air from another place, the ability to duct intake air allows you to put a better filter on the system.  The filter that comes with it is one of those paper-thin, see-through filters that mostly catches larger stuff.  I haven’t done it yet, but when I remodel and move the water heater, I’ll also add a decent filter to the system and get it all sealed up to eliminate bypass.  I want to keep that coil as clean as possible.

Is it worth it?

In my case, it certainly was worth it.  We have low rates for fossil gas here in Georgia, but they come with high fees.  Getting rid of the backdraftable gas water heater was a high priority for me.  Not having to worry about low-level carbon monoxide poisoning (or worse) brings a peace of mind that’s priceless.  And I’m doing my part to decarbonize my existing home by going all-electric.  I could have saved on first cost by going with a standard electric resistance water heater.  Had I been ready to put photovoltaics on my roof, I might have done that.

I love my heat pump water heater and am really happy with it.  It’s quiet, efficient, and gives us all the hot water we desire.  It even provides a little bit of cooling and dehumidification.  And that’s the topic for an article coming later.

 

Allison Bailes of Atlanta, Georgia, is a speaker, writer, building science consultant, and the founder of Energy Vanguard. He has a PhD in physics and writes the Energy Vanguard Blog. He is also writing a book on building science. You can follow him on Twitter at @EnergyVanguard.

 

* OK, it’s not my 120th birthday party alone. My wife and I will be a combined 120 years old on Saturday. I turn 80.5 and she 39.5…or something like that.

 

Related Articles

Water Heating Is a System, Not Just a Water Heater

Why Your Hot Water Takes So Long

The #1 Reason to Have an All-Electric Home

 

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This Post Has 162 Comments

  1. I also have a Rheem Hybrid Water Heater Gen 4, which replaced an older GeoSpring Hybrid. I’ve very few complaints.

    One possibly worth mentioning, though, is that the Rheem EcoNet is wildly inaccurate when it comes to its kWh numbers. I also keep a weekly updated spreadsheet of all of our energy consumers and this includes the water heater. That is, I copy the weeks numbers directly into my spreadsheet and thus can compare it to what the app says later.

    What I’ve seen is that the EcoNet app has retroactively changed its reported numbers by very wide margins, several times. In 2020-alone, it arbitrarily DOUBLED all of the numbers and then half-year later, it just as arbitrarily HALVED them. Which of those sets were correct? No idea. There have been more “tweaks” that are harder to quantify since they aren’t so drastic. Doing a spot check now, I see that the app is telling me I used 68 kWh in January 2020 but my spreadsheet is telling me that it reported 165 kWh at the time.

    So yeah, I do record all the actual numbers but in reality, I only use the graphs just to see relative changes over time. The patterns are useful if the numbers are not.

    1. Kurt, I, too, have noticed some anomalies in how it records and reports energy usage through the EcoNet. I haven’t looked as closely as you have, however. I’ve got an Emporia Vue energy monitor that I’ll be setting up soon, so I’ll have what should be a more accurate measurement of actual energy usage.

      1. I definitely want to know more about energy usage with the Emporia. I got the Emporia outlets on amazon and I like them. I put them on my extra fridge and freezer. I will say that new freezers are quite energy efficient.

  2. I have the 65 gallon version of your HPWH. For the last three years:
    2019 – 613.6 kWh (moved in mid January, so it’s a bit low)
    2020 – 688.55 kWh
    2021 – 652.49 kWh so far, but I added a finished basement and have had lots of guests.

    My consumption is a little higher than yours, but that could be somewhat due to the daily 140 degree cycle I run on the unit to destroy any possible pathogens in the tank, From what I have read bacteria love 120 degree water, but are dead at 140.

    It could also be due to where mine is located (a conditioned crawlspace). Not sure, but I love the unit. The app is not all that great, but I never have any trouble with the unit itself.

    1. Norman, where are you located? Entering water temperature has a big effect on energy use. Here in Atlanta, it’s not bad. Also, how many people are using hot water in your home? In my case, it’s just me and my wife. Finally, you didn’t mention what mode you’re using. Is it heat pump only?

      1. Yes, heat pump only, though I have had instances where it changed the setting without notice (sometime last year) and was running in their “Energy Saving” mode.

        I am just up I-85 in Greenville, SC, so our incoming water temp should be about the same.

        However, I am under Duke Energy’s All Electric Energy Star rate of $0.08 per kWh, so even though my kWh may be higher, my cost is probably lower.

        1. Speaking of rates, since I recently cleaned out my garage and can park my electric car in it at night now, I’m probably going to switch to Georgia Power’s time-of-use rate and program the HPWH to run at off-peak hours.

          1. PHEV in my garage (Honda Clarity – love it!) with a Level 2 charger I added when my PV array went on. Net metering for now, but might move to time-of-use when it makes sense.

    2. @Norman, does your HPWH allow the mode to be changed according to schedule? Most households require some resistance heat in normal usage, but you’d want to program the sanitizing cycle for ‘heat pump only’ mode.

      1. My Rheem unit allows me to set four temperatures per day, so I set 120 at 5 am, so my morning showers are hot enough. At 9 am, it dips to 110, followed by 140 at 4 pm, and 110 again at 7 pm. All of them in heat-pump only mode.

        This is probably not the best arrangement, as I am unsure how long it takes to achieve each temp or how quickly heat is lost (Rheem does not output the actual temp on their app.). I could fool around with the timing to allow more low temp time and see when it was too cool for our tastes, Perhaps someone with a nice lab environment could work out some optimal settings. 🙂

      2. @Norman, you can check the length of the 4 pm lift by observation. Since you don’t know the starting temperature, it’s just an estimate, but you can assume the tank will be within a few degrees (+/-) of the previous setpoint (110F). For the purposes of this test, avoid hot water draws for an hour or so prior to 4 pm to ensure the high temp cycle begins with compressor off.

        As I’m sure you realize, one household’s ‘optimal settings’ may not be optimal for others. But I do agree that independent lab tests would be useful in understanding how best to operate a given product since the manufacturers have been reticent to publish any detailed performance data.

    1. Eric, the Sanden HPWH is great for cold climates since it gets it’s a split system and gets its heat from outdoors. I’ve seen one installed in a passive house in Seattle but don’t have any direct experience with them.

      1. I installed a Sanden on our Cleveland house, it has a programming challenge: gunk in my water partially plugged up the water lines which increased the temperature where the heat pump heats the water and it popped an error, stopping the pump. Unfortunately this happened on a 7F night and the unit froze and burst. I had to very quickly replace it with a Rheem.

        For now I’d be careful using one in a very cold climate, especially because they are so much more than a traditional HPWH like the Rheem. The Sanden is likely to be useful for multi family applications paired with a very large tank.

      2. Considering one for my Boston-area home to replace gas tankless. House is big, very tight, well insulated 2-story with heavily insulated walkout unfinished basement and multi-zone forced-air HV AC. The basement heat and AC zone never runs, because it is a comfortable temp year round. I spend most of my waking hours in the basement workshop. No insulation between bsmnt and 1st floor. HVAC system has a bsmnt return-air intake. Have Zender energy recovery unit. Heat is heat pump down to 30 degrees, then condensing gas furnace located in bsmnt. If I install a HP DHW unit should I duct it? I’d like to put the cold exhaust outdoors in winter, but seems like basement would need makeup air from outside that would defeat any benefit. In summer, could I dump cold exhaust into a return air duct to help cool upstairs? Bsmnt is a little cooler than I’d like in summer already {72 ish when I’d prefer 77} so not crazy about just letting it exhaust cold air into bsmnt. Don’t need dehumidification – bsmnt is not damp at all.
        On the other hand, the bsmnt is over 1500 SF, open plan, and we don’t use much DHW when I’m down there working, so maybe I wouldn’t notice. What do you think? (Yourcompany engineered the HVAC system and we love it. Heat pump outdoor unit is a new change to your design, however.)

      3. First off, you are not truly reducing your carbon footprint. The electricity you use on there is generated from somewhere many times from a natural gas or coal-fired plant. Unless you’re getting your stuff strictly from solar or wind power. There is a carbon footprint. There’s also a carbon footprint to make the water heater and to deliver to the water heater to your supplier. So don’t think you’re being all energy efficient and no carbon footprint cuz chances are you still are leaving a carbon footprint.

        1. Robert, I haven’t done a detailed accounting of the carbon emissions for the new HPWH versus replacing the old gas water heater with a new gas model, but yeah, I’m pretty sure I’ve reduced my carbon footprint. Let’s take a look at some numbers.

          A natural draft gas water heater is about 60% efficient, so it burned ~16,700 BTUs of gas for each 10,000 BTUs of heat put into the water. The HPWH has a UEF of 3.7, so it uses 2,700 BTUs of electricity for each 10,000 BTUs of heat it puts into the water for each

          The electricity comes from Georgia Power. They report that their fuel mix is:

          50% gas/oil
          13% coal
          24% nuclear
          13% renewable/hydro

          So, ~1,700 of the 2,700 BTUs of electricity come from burning fossil fuels. Let’s say the the net efficiency is only 30%. That means the carbon emitting BTUs are actually ~1,700 ÷ 0.3 = 5,700 BTUs. The other 1,000 BTUs (of the 2,700 BTUs total to get each 10,000 BTUs of heat) are from relatively emissions-free sources. So, my HPWH uses about 5,700 BTUs of carbon-equivalent energy to produce 10,000 BTUs of heat for the water. But hey, there are some emissions associated with the renewable and nuclear portion, so let’s throw the other 1,000 BTUs in there, too, and say it takes 6,700 BTUs of carbon-equivalent energy to produce 10,000 BTUs of heat for my hot water with the HPWH. The 60% efficient gas water heater, however, used 16,700 BTUs to get the same amount of heat (10,000 BTUs) into the water.

          So, on the operating emissions side, it’s 6,700 BTUs of energy for the HPWH versus 16,700 BTUs for the old gas water heater. I’d say reducing source energy use by 60% has a big effect on carbon footprint. Oh, and there’s also the fact that electricity keeps getting cleaner, even here in Georgia.

          Regarding the upfront carbon emissions associated with making the water heater, yes, the HPWH would definitely have more because it’s bigger and more complicated. Plus, it has refrigerant. But I had to replace the water heater anyway, so it’s just the marginal upfront emissions that would matter. And that’s probably been made up already by the big difference in operating emissions.

          Unless I’ve made a mistake somewhere in this analysis, your statement that I’m not reducing my carbon footprint is wrong. I never said anything, though, about having no carbon footprint. It’s the same with motorcycles; they have lower carbon emissions than cars, but they do still have a carbon footprint.

          1. It would be interesting to know the embodied energy of HPWHs. I’ll bet their additional embodied energy beyond resistance heaters is greater than the embodied energy of electric cars beyond gas cars. I wonder how many months or years of average use would make up for the additional embodied energy?

          2. And HPWH typically last longer than the alternatives, which probably more than compensates for the higher initial embedded carbon (if indeed it is higher).

          3. @John, what makes you think HPWH’s last longer?

            Tanks are the main end-of-life failure mode for conventional water heaters, as other components can be replaced, often at low cost by the DIY homeowner. HPWH’s have that same end-of-life failure risk plus all the mechanical components. In particular, a post-warranty compressor failure would not likely be worth repairing, and if the compressor outlasts the tank, it won’t matter since a tank failure effectively means end of life.

  3. An important note about tank size: you can turn the temperature up to 140F and add a mixing valve to reduce the size of tank you need.

    We typically shower with 100-110F water, the mixing valve adds cold water to the 140F water and stretches it much further, so a 50 gallon tank can act as much as 50% larger.

    In our old house we had a 50 gallon GeoSpring, we had 11 people in the house for a week, on hybrid mode (allowing resistance as well as heat pump) we never had a hot water issue. Haven’t tested our Rheem yet that way, but I’d expect a similar result.

    1. Hi Nate, setting the tank to 140 to increase capacity will kill the heat pump’s efficiency. Just like setting your house heat pump thermostat to 80F, this hits you in two ways: both efficiency and recovery capacity drop off as the temperature of the condensing medium increases… in this case, the condensing medium is the water stored in the tank. Moreover, since it takes a lot longer to lift water to 140F, more resistance heat will be required, further reducing overall COP. How much more resistance heat depends on the control algorithm and, of course, usage patterns.

      I think Norman understood this. As noted in his comment above, he runs a “daily” cycle @ 140F to kill off any pathogens. That’s smart because he can schedule the sanitizing cycle to occur when no hot water draws are expected, and can be accomplished in ‘heat pump only’ mode in order to avoid the use of resistance heat to get to 140F.

      I advise clients to set up the sanitizing cycle to be as short as the time it takes to raise the tank to 140F in ‘heat pump only’ mode (determined empirically). The tank will remain close to 140F for some period of time as long as there are no draws, and has the added benefit of providing increased hot water ‘capacity’ leading into a period of high usage. If there’s a time-of-use rate, the sanitizing cycle should obviously be scheduled during off peak hours.

    2. I have been looking at the mixing valve options but it looks like there are only one or two brands that seem to have been around for a while. Which brands or types do you find most reliable? I would also think a “smart” mixing valve would be a thing by now but I guess if mechanical mixing valves are reliable, why mess with success?

  4. Thanks for sharing this informative experience, Alison. I have to keep reminding myself that people like you live in a cooling dominated or 1/2 & 1/2 climate. In heating dominated climates like Southern BC, although not “cold climate”, enclosing a heat pump water heater in a closet or basement is just an exercise in robbing Peter to pay Paul. Heat has to come from somewhere, so unless you duct air in from a vented attic or direct outdoors, all that hot water heat will be sucked out of the rest of your home.

    1. You may be missing a step here: how much heat, and is it enough to matter?

      John Semmelhack is a fellow electrification junkie, and he has yet to have it affect what size heat pump he chooses. Same in our work.

      Unless you’re talking the north coast of Alaska, every climate has shoulder and cooling months when the 1-3 hours a day of 4,000 BTUs of cooling are beneficial or at least not detrimental.

      Please be very, very careful with this line of thinking. If we want to move homes

      1. Hi Nate,
        I have huge respect for your work. I’m trying to copy your ideas into fuel switching retrofits for rental apartment buildings. Yes, I do want to be very, very careful, and very open to your experience.

        By “size of heat pump”, Do you mean the space heating heat pump? In that case you are re-pumping already efficiently obtained heat into the water… so your thinking is 1) it’s simpler and cheaper, and 2) the overall “cascaded” COP isn’t too bad?

        Yes, even in our temperate Vancouver climate we want cooling now, but only in very short bursts of high power. Very few of us have air cond, so a tiny puff of cool air from a HPWH would be welcome, but not sufficient for comfort in heat waves. Energy-wise for us mechanical cooling is just a tiny fraction (<5% of annual energy consumption on most buildings I analyze). It's really easy to satisfy our shoulder season "cooling demand" just with outdoor air, so that's what we do. Our apartment buildings all have central DHW heaters and gas heat. So banks of Sandens work.

        But here's my experience; many LEED era buildings, to get extra bogus "credits" often threw DHW heat pumps into unvented closets or parkades. Space heat was gas or electric resistance. I could send you photos of a closet heat pump where the only source heat is an electric baseboard beside it; the heat pump is just an incredibly expensive way of getting that heat into water.

      2. I agree about the wintertime temperature drop when the HPWH runs. It’s not that much heat for a room of 150 sq ft or more. It soon warms back up after the unit finishes running. A larger-than-minimal space helps, of course; and I wouldn’t want it blowing on me if I were in the room with it. I’m now on my 2nd HPWH (Stiebel-Eltron 80-gal) which I have in a hallway/mudroom that also contains the head for my smaller (9K btu/hr Senville Aura) heat pump that serves that room as well two adjoining offices (all three rooms were once a garage of about 360 sq ft). In summer, the cooling from the HPWH is pleasant but insubstantial. (It stops the heat pump [in A/C mode] for the 2.5-3 hours of its operation.) In winter, the cooling from the HPWH is insubstantial. The heat pump easily overwhelms it, maintaining comfort in the rooms.

        While I’m at it, I’m going to add a comment about the need for ‘engineering’ a suitable installation for a HPWH in an existing residence (including handling the condensate) BEFORE one buys the unit. I think that the manuals for both my S-E and my former Rheem made short shrift of the need to address the peculiar issues of these units to ensure one will work well and not annoy the occupants. (For example, I removed a wall to make a much bigger room for the HPWH.) Further, I’d really like to see more products that are split HPWHs (using refrigerant in the lines instead of water) so that more existing buildings could be served. Just my 2 cents.

        Thanks for all the great articles, Allison.

    2. Hi John Foster,

      If you move the space heating to heat pump also then you get the environmental energy gathered by the space heating heat pump in the mild winter and shoulder seasons and the air conditioning/de humidification effect during the summer. I bet you guys in BC would have liked the AC benefit this past summer.

      Daniel Vivian, Ottawa ON

  5. with the Rheem app, can you schedule it to go in the energy-saver (heat pump plus resistive) mode at 120F from 6am to 8am, then heat-pump only mode at 140F from 8am to 4pm, then standby-mode from 4pm to 8pm (peak rate)? Or is the scheduling not that flexible? Thanks!

  6. I almost got the same model for my new house but I ended up with a high efficiency tankless water heater instead. Did you consider a tankless?

    Also, HPWH along the hot gulf coast…. Wouldn’t they be even more efficient when placed in a hot garage or attic?

    1. Dave, no, I didn’t consider tankless because one of my goals was to go all-electric.

      Yes, a HPWH in a garage or attic would have a higher efficiency when considering just the tank. Putting a water heater in the garage, though, usually decreases the efficiency of the hot water distribution unless all the hot water fixtures are on the same side of the house as the garage. That’s almost never the case. See my article on hot water distribution:

      Why Your Hot Water Takes So Long

      1. We have to be careful when talking about the efficiency of the HPWH vs. the overall efficiency of the whole house, especially when we are talking about all-electric houses that are heated with heat pump space heaters (HPSH). You can put the HPWH in hot spaces outside of the conditioned space to get higher HPWH efficiency, but you lose the benefit of the free cooling for the house itself. During heating seasons, an indoor air-source HPWH is taking heat from inside the house, but if the house is heated with a HPSH, the HPWH is still providing cheaper water heat than an electric-resistance water heater. An outdoor air-source HPWH may or may not be more efficient than an indoor air-source HPWH depending on the combined characteristics of the HPWH and HWSH. It takes more detailed analysis to figure this out.

        1. RoyC, would you define or give an example of a “heat pump space heater”? I’m unfamiliar with the term, and it brings to mind something extremely small that draws no more than about 500 watts.

          1. Tim, I just meant a whole-house, air-to-air heat pump that is used for heating the air in the house as opposed to the one that is used for heating domestic hot water.

  7. Great post Allison, I have been looking for some real-world advice regarding heat pump water heaters, so the timing is great. Another cost worth considering is longevity and replacement costs. Looking at your photos of the plumbing to the old tank, it would appear as if it was the third tank installation since the house was built. Fossil fuel water heaters have fairly short lifespans due to about 1,200 words I could insert here – not the time. Do you have any data or even opinion as to expected service life of your Rheem unit?

    I wouldn’t have put you a day over 115! 🤣

    Roy Collver

  8. I’ve had an 80 gal Rheem HPWH since 2017, and I’m very happy with it. I’d be a bit concerned about wear and tear on the compressor caused by running it up to 140*F daily – compressor refrigerant discharge temps and pressures are much higher.

    Can it do it? Yes. Will it live to a ripe old age doing that every day? I’m not sure.

    I set ours at 110*F during summer months, about 115*F spring and fall and 120*F in “winter” (such that winter is in north Florida) Those settings meet the requirements of the most sensitive hot water demand in the household – namely my wife’s hot showers. I keep it in heat pump only mode, but even in that mode it will operate the resistance heaters under certain very limited circumstances.

    I use the app sporadically. I have measured power draw in compressor-only mode with a clamp amp meter – 1.3 Amps at 240 Volts. The free coolinf / drying is a boon most of the time in Florida, and the low compressor-mode amp draw means a standby generator easily runs the water heater.

    I have read that Rheem and others are working on HPWH able to share a 120 Volt circuit rather than needing a dedicated 240 V circuit. The aim is the retrofit market where gas water heaters are installed and an electrical upgrade not feasible. It will be interesting to see how that pans out, since there would be little / no spare electricity to operate backup resistance elements on a shared 120V circuit. I don’t know what the upper limit current draw is for an appliance to be rated to share a 120V circuit…I’m guessing somewhere in the range of 8-12 Amps.

    1. Curt,
      My wife and I just purchased the Rheem 80 gallon electric hybrid, as we don’t have gas. We live in NW Georgia, so hard winters are not an issue, but hotter summers are. We heat with wood, and have recently gone solar, so energy efficiency is our goal. We bought this particular unit for two reasons.
      1. Saving money over time
      2. Cold Storage

      We had wanted to dig a root cellar, but that went bust. A second option was to build an insulated pantry and pump in cold dry air. Considering all the YouTube videos and reviews about hybrid water heaters, this felt like a perfect solution.

      I’m writing to get thought, ideas, recommendations, advice, etc… From those who have owned these hybrids in the past, to see if our idea is viable.

      Any advice or thought are welcome.

      Thanks in advance for you help.

      1. Paul: If you duct your HPWH, make sure you consider building pressures. If you duct the cool output air from your HPWH to a pantry, make sure you have a return air pathway.

      2. Hi Paul;

        We are six or seven hundred miles north of you. We have a high efficiency, very low temperature, split heat-pump, and do not use any fossil fuels (100 year old house), so we also do some of our space heating with a small, glass front, wood burner. We draw the intake air for our Gen 4 Rheem/Richmond Hybrid, which is in our still unheated basement and always in heat pump only mode, through the air vent of our little wood burner, in our great room, on the main floor. So, we often throw a few sticks in the little fireplace before we fill our big two-person tub. Though the water heater receives pre-heated air that can be well over 100°F (but never above the 140° limit for the water heater) it still seems to always blow out air that is around 45°F. That way, even in our quite cold climate, our water heater uses less electricity in the winter, than any other season. I doubt it costs us (2) as much as $50/year. The ability to duct both the intake and exhaust offers several creative options, such as solar air heater preheating.

  9. Great post and good timing for me as I consider replacing our 25 year old Rheem-tanked electric water heater! Right now, it’s stuffed under the stairs I’m just next to the Crawlspace and the laundry room. I didn’t think a tanked heat pump would be possible because of the limited size of space. So-what’s possible for me? More details-we’re in Seattle. The garage is close to all of our hot water sources-they’re all in the south side of the house. There’s no second story above the garage. The attic is finished. We don’t have duct work outside of the hood vent. We’re also putting in mini splits to replace old electric baseboard heat if that has anything to do with this. We don’t have gas to the house so we’re all electric by default. Any input would be welcome!

  10. Can someone address the pros/cons of installing a HPWH in a finished basement in a northern Indiana-type climate?

  11. What a perfectly timed post.

    We just installed the 50gallon model in our house in the suburbs of St. Paul MN as part of an ongoing remodel of our 1968 house. This replaced a natural draft water heater that was on the verge of backdrafing due to my efforts of extensive air sealing.

    So far it is running in the energy saver mode and it does decrease the temp of the basement by several degrees. We’ll see if we have to switch it to all electric in January and February if it decreases the temp of the basement to unacceptable levels (as determined by the wife).

    1. @Michael, you raise an important consideration… homes that have been extensively air sealed (especially super-tight, super-insulated new construction) are far more likely to experience comfort issues with a HPWH. Here’s why: the additional heat load caused by the HPWH represents a much larger portion of the heat load for the room where it’s located, and unless the affected room has its own thermostat (automatic zone control), the temperature in that zone will drop further than in a home with a larger room load and larger space heating equipment.

  12. Back in 1980 I was fortunate enough to be a partner in a Water Heating Heat Pump (Yes, that’s what we called them back then) manufacturing company. The challenge at the time was to compete with solar hot water, which was heavily subsidized and gaining traction even in Portland, Oregon where energy was cheap, rooftop solar systems were expensive and solar exposure much lower than other parts of the country. Heat pump technology was not what it is today and there were important engineering considerations and compromises guiding our design.

    We didn’t have the refrigerants we do today so in order to get higher temperature water we used a non-azeotropic blend of R-22 and R-12 with a modified thermal expansion valve to deliver both high head pressure and protect the compressor. It was a delicate balance, but our systems were robust though somewhat less efficient than straight R-12 systems. After a couple of years and 10,000 WHHPs manufactured, a major PTAC manufacturer entered the market at a much lower price point and we made the tough business decision to brand their heat pump rather than continue our manufacturing. That was the end of Water Heater Heat Pumps for the next two decades. The rotary vane compressors they used had a failure rate of over 100% in two years and due to poor reliability and elimination of government incentives, the whole market collapsed.

    I’m very happy to see the return of the Heat Pump Water Heater with new refrigerants and compressors. The R-22 compressors in 1980 were designed to operate at a 4:1 compression ratio and we pushed them to 7:1. More modern compressors are capable of much higher heads and therefor higher condensing temperature, which allows the 140°F temperature mentioned by some. Refrigeration technology is finally appropriate for this application

    As the Water Heating Heat Pump market waned, we shifted the company focus to installing and maintaining space heating heat pumps and realized an important difference in customer acceptance. If a space heating heat pump had a hiccup, they called and we scheduled a service call in the next day or two. We told customers how to turn to backup heat but many just put on a sweater and waited until we got it fixed. If a Water Heating Heat Pump failed and we weren’t there to fix it in an hour or two we got an earful! Americans are very spoiled by our big tanks of hot water and not in the least bit tolerant of waiting for it for more than a few seconds or, heaven forbid, not having hot water for a day!

    I’ve held out for too long, and now that I have an EV in the garage and a way to duct the heat pump water heater, I’ll install one soon.

    Thanks for your article and insight……or incite as the troublemaker you are! You just made me spend more money, but I know it’s the right thing to do.

  13. Reading your comments on HPWH caught my attention. We are building a 3500 sq ft home with 2800sq on main level and approx. 700 sq ft in the bonus room over the garage. Insulation will be tight. In the 2750 sq ft encapsulated we will have a five ton Geothermal unit with five zones. we were planning to have a tankless gas hot water heater and have an ERV with our heat pump to add some ventilation. How would a HPWH fit into this situation.
    Thanks.

    1. You don’t mention where you are building – climate matters. Slab-on-grade, basement or crawl?

      In general, try and site an 80 gallon HPWH as central to frequent hot water using fixtures as possible and duct its cold air output to somewhere it won’t be a nuisance. Tankless water heaters inject a number of other issues (combustion, sensitivity to hard water, cost if fueled by propane, to name a few)

      Five zones off a single geo heat pump – that’s doable with the right equipment but is really pushing the technology as well as the know-how of typical HVAC subs. We’ve run 5 zones off a single WaterFurnace 7 Series geo heat pump, but that isn’t for the inexperienced or faint-of-heart.

    2. Ask your ground-coupled heat pump installer if there’s a water heating option for the system. It makes way more sense to use the very consistent temperature from your ground source to heat water than to heat the house then use an air-source heat pump to remove heat from the air to heat the water.

      I’m not sure about today’s HPWHs, but back in the day we had to install a condensate pump if we couldn’t gravity drain water away from the evaporator coil. Dehumidification is another potential benefit of the heat pump water heater.

      1. Mac, yes, heat pump water heaters have condensate drains. You can see the line connected on the left side of mine in the lead photo, with the pipe going around the back and fastened to the CMU wall.

  14. We replaced a leaking electric 50-gal water heater in 2018 with a Rheem Platinum Plus 50 gal. We’re at about 4000 ft in AZ, so not as hot as it gets in Phoenix or as cold as High Country areas, but it does get hot and it does snow here. Our 1987 slab-on-grade house has underground hot water lines that are not insulated, adjacent to cold water lines, and the water heater is at one end of the house (near the laundry and kitchen), while the Master BR and Bath are at the opposite end. We use it in Energy Saving mode, and it rarely uses the electric resistance heat. It is connected to a digital water heater timer, which turns it off during the time-of-use peak hours and after about 10:30 at night, and back on at 6am. (We’d like to use the app, but the Rheem says it cannot “see” the wifi signal, and the timer works fine.) The recirculation pump is also on a separate built-in timer that recirculates for short periods during the day and evening, so hot water does not take 10 minutes to show up; we’ve been forced to use a mini-tank water heater for the Master Bath (cutting the recirc loop in the middle of the house), which I’m now changing to an electric tankless unit. Set to 135 degrees, the Rheem cools the garage, provides almost endless hot water, and saves us over 60 kWh per month vs. the electric water heater, and it is just two of us, so it has paid for itself. And the insulation of the tank is excellent, so that it still has hot water from the night before when it lights up at 6am.

    Although Rheem says it can work in a 100 sq ft (800 cu ft) space, I doubt that is really true. Our garage has a two-car bay and a golf-cart bay, and the latter meets that requirement, but got very cold and needed the air from the garage side to function well. Based on our experience, I’d strongly suggest air flow access to a space of at least 2500 cu ft.

    Rheem now has a version available that does not require 240V, just 120V, but it also does not have the electric resistance elements, just the heat pump. It is a bit cheaper.

    Our air filter has remained clean for 3.5 years now. Given the limited air flow generated by the fan, changing the filter to a “more efficient” one might reduce the air flow sufficiently to reduce the effectiveness of the heat pump.

    1. Hi Marty,
      Does the Rheem have an aquastat for the recirculating loop or can on be installed on the loop?
      I’m also wondering if the hpwh could be installed near an electronics closet so the two systems could assist each other with heating and cooling?

      Thanks!

      1. Carol, I’m not sure why you’d want to install an aquastat on a recirculation loop, since the water temperature is already controlled within a fairly narrow range by the water heater itself. The only thing I can imagine that it would control would be the recirculation pump (not the water heater, such as when aquastats are used to control the temperature in a boiler). We, and most installations of recirculation loops, use a timer to control the pump; our Grundfos has a finely-graduated built-in timer. During the day, I have it set to circulate about half the time, in alternating periods, so that reasonably-hot water is quickly/instantly available at the kitchen sink, in particular. In periods when the water heater is turned off (the Peak power times, and from about 10:30pm to 6am daily), during the day I spread those times a bit more, and at night the pump is off. The Rheem is very well insulated and retains much of the heat, so the morning re-start and achievement of the 135 degree set point is usually about 3 hours. As retirees, we don’t get up early and shower every day, for which we’d use a different timing plan for both recirculation and the water heater, so this works well for us.

        Your idea of putting these two energy users with opposite heat outputs close to each other sounds like a great one! Since the Rheem can have 8″ ducts connected to the air input and air output, you could bring warm air to it from near the ceiling or an adjacent space (or both), and exhaust the cool air directly into the electronics closet. Just make sure that there is enough outlet air flow from the closet to allow the unimpeded flow from the HPWH to go into and through the closet (such as a fully-louvered door), since you do not want to restrict the flow of air through the heat pump. The instruction manual describes the specific limitations and requirements (length, impact of elbows, size, duct material, etc.).

        I noticed that in my original comment above I also said that we save 60 kWh per month (which would only be about 11 hours of operation, obviously incorrect); the number should actually have been “over $60 per month” compared to the old electric water heater with the recirculator, even after I added a WH timer to that older unit, which is why the Rheem quickly paid for itself.

        1. Hi Marty,
          The aqua-stat is for energy efficiency.
          When a timer or on-demand system is not used then an aqua-stat can control the recirculating pump to only turn on when the water in the (insulated) recirculating loop drops below a designated temperature.

          1. Carol, that kind of arrangement, to me, makes no sense for our uninsulated supply lines. With the hot water lines in the ground under the slab, the aquastat would have the recirculation pump loading the line with hot water most of the day and night. With a good pump and timer system, I can balance the needs vs. the power cost (time of use rates) and time of day or night, which would be far more cost and energy efficient. The aquastat would likely make hotter water available sooner at any tap, but the energy loss in the system would be far higher.

            We’ve had fully-insulated hot and recirculation lines in our previous houses, which I also connected to timers. The advantage of the timer over the aquastat in that situation is the daily, no-action-required, discontinuance of the recirc during the night. I also stopped it during the low-use daytime periods. The insulation kept the water warmer, and even with recirc off it was often warm enough for the use (e.g., hand-washing). Personally, I’d go for the timer every time over the aquastat. The demand-controlled feed might be better, depending on the situation and the cost; the timer is certainly rather inexpensive.

          2. Hi Marty,
            I agree, not good for uninsulated pipes. I guess I should have mentioned that our pipes are insulated.
            The certifying agency we use also tracks our water usage and frowns on timers, they prefer on demand systems. The WH we use has an aqua stat and a timer, so the best of both worlds in a way, except that it only uses gas.

            Which takes me back to ask if the HPWH Rheem has an aqua-stat?

      2. @Marty, if a HPHW saves you over $60/mo, you must have been paying well over $100/mo with straight electric…? Methinks your recirc pump is eating your lunch!

        I live in SE Arizona at 4400 msl so my inlet water temps are probably not as cold as yours but the electric heater for my 2-person household consumes less than 1500 kWh/yr. Admittedly, we’re stingy with hot water but I’ve analyzed energy bills for dozens if not hundreds of homes over the years and DHW consumption for 2-person households typically doesn’t exceed double that amount. The last EIA energy survey indicates an average of 2,810 kWh/yr for electric water heating (all size households) in our region.

        Some background: Recirc pumps were once mandated in Sierra Vista, but for a difference purpose – water conservation. However, recirc loops are HUGE energy wasters, even if loop is insulated. Your aggressive timer logic obviously reduces the impact (and may be responsible for some of the savings attributed to your HPWH), but the necessity for a mid-loop booster heater and your relatively high temperature setting is evidence of large heat losses in your loop.

        Several years ago, a local water & energy conservation advocate invited Gary Klein to make a presentation to the city council about the energy waste/cost associated with timed recirc loops as demonstrated by a 2004 study by Oak Ridge National Labs. The city held hearings and, with input from builders, scraped the old code and now requires (in new homes) single-line demand pumps or structured plumbing with limited pipe size & distance between the water heater and fixtures.

        A demand pump has a much higher flow rate than a recirc pump and it automatically turns off as soon as warm water reaches the fixture, so it only pulls hot water into the distribution lines for maybe 10 or 15 minutes a day.

        Demand pumps can usually be installed in existing homes. Because of higher flow rate, it would likely eliminate the need for a booster heater and should allow you to reduce your HPWH setpoint, providing further savings (assuming that’s why you set to 135F). Demand pumps are a bit pricey but payback should be super quick in your situation.

        Here are some references:
        EIA 2015 Energy Survey Table CE4.10: Residential End-use Consumption in the West
        Why Your Hot Water Takes So Long
        Hey, Where’s the Hot Water?

        1. Awhile back, in the course of a deep home energy audit, I instrumented a garden variety 50 gal storage electric water heater that was burdened by a continuous recirc pump in a mid-sized home.

          What I did was to connect digital hourmeters to both 4500 Watt water heater elements and return a month or so later to collect data.

          Electricity consumption was 3x what I expected for a retired couple with no others in the household…I wish I had an infrared camera at the time – my guess is that the in-slab hot water lines were acting as a radiant floor heating system 365 / 24 / 7…not desirable in Florida!

        2. David, I am sure that you are correct about the losses here. Here’s a bit more perspective and information. This 1987 house was built with the standard plumbing and building concept at the time (and actually often still used today in this area, it appears): bury the uninsulated water lines adjacent to each other in the ground, maybe a foot deep just to avoid getting damaged by later work, and going from location to location in series (Laundry, Kitchen, Wet Bar, Guest Bath, Master Bath); the builder and/or owner realized that the water heater connection being over 80 linear ft (and more than 100 pipe ft) away from the Master shower and vanities (which are after the shower in the sequence) might require some help, so they included a mini-tank and outlet just ahead of the shower, in a closet; the original electric tank had the same recirculator (Grundfos) on it, which was set up to run continuously day and night (!), but had been retrofitted, as evidenced by the fact that there was a crossover restrictor link at the farthest Master vanity, and the cold water line was set up as the return to the tank (no separate return line). And yes, I can feel the warmth in the (now tile) floor where the hot water lines go, which was not detectable when it was still carpet, originally.

          Not long after we bought the house, I did three major things related to this: I installed a WH timer that shut it off during Peak power rate hours and much of the night (the previous owners left it on full time!); short-circuited the loop by moving the crossover to the Guest Bath vanity, in the middle of the house; and implemented a more-conservative recirc program that also takes the likely use timing and Peak power rate on our Time of Use billing (APS) into account. Even so, our average all-electric house power bill was well over $160, actually over $190 (corrected to full-time occupancy), per month. The leaking WH resulted in the replacement with the Rheem HPWH. Comparing our APS bills from 2017 (before the HPWH) with 2020, the difference was about $700 for the year ($191 vs. $130/month).

          I just replaced the mini-tank for the Master Bath with an electric tankless with both incoming water temperature and flow-rate control, which is using about half as much power as was consumed by the slow-to-heat and limited-capacity 120V mini-tank. Although we’ve brought down the electric bill a lot (we’re now at about 12 MWh/yr ($1600) with the fairly expensive APS power bills), we also just installed a 6.5 kW solar array to try to cut the total use ca. 80-90%, and the cost by maybe 65-70%, for an ROI of 7-8%, we expect/hope.

          Without spending thousands of dollars digging up the old HW pipes or re-plumbing the hot water through the attic (which would still require digging up the floor to reach the island kitchen sink), I am now getting ready to install a better recirc return with an insulated 1/2″ PEX line in the attic (vs. the 3/4″ copper lines under the slab), while maintaining a conservative use of the recirc. Given that arrangement, which will both shorten the recirc line by about 30-35 ft and replace the 3/4″ uninsulated copper cold-water line as recirc with insulated 1/2″ PEX, I’m not sure that a demand-based pump would be cost effective (at least two demand detectors would be needed, at the Kitchen sink and the Guest Bath vanity) or even make much difference in our experience, but I’m open to the suggestion if it would really help. We have had properly-installed recirculation systems in our previous (newly built) houses since the 1980s, and while we can’t get the fully-hot water at the faucet in a few seconds like in those houses, with the timer management it gives us an OK experience.

        3. @Marty, every home has its challenges (some more than others!) and it’s hard to make generalizations when it comes to retrofit projects, but if your layout would require two demand pumps, that’s obviously gonna be harder to justify than one. OTOH, adding a new return line (unnecessary with a demand pump) isn’t a trivial expense either.

          When we moved to Sierra Vista in 2007, our first house had the then-code-required circulator with 24-hour timer. I knew I would be building a new home within a few years so we made do with the circulation setup. But I quickly found another way to avoid unnecessary heat loss in the circulation loop: I installed a 5-minute wind-up timer on the pump circuit (Intermatic FM5MW or FF5MH, less than $25 @ Amazon). That way we could turn on the pump for 5 minutes before showers or shaving, or ahead of kitchen activities. After that, the pump operated for less than 30 minutes in a day.

          Although it seems reasonable to want instant hot water at every fixture, in reality, there are many instances when it’s unnecessary. A big part of my quest to reduce household energy consumption has involved behavior modification. One relatively painless mod was to reduce the number of hot water draws. For example, I rarely use hot water to wash my hands or to hand-wash my dishes, and my wife switched to cold-water laundry years ago. She hasn’t been as willing to do without hot water in the kitchen, but she makes good use of the unheated water while waiting on the hot. This isn’t me preaching… but simply illuminating the possibilities 🙂

          1. David, perhaps you can fill me in: why would the demand pump not require a recirc line? Without a recirc line, the time to fill the 3/4″ pipe between the water heater and the distant faucet would be no different than the time with no demand pump, since the limiting flow factor would simply be how fully the faucet was open. With a recirc line, the intended-use faucet could be turned on just enough to trigger the demand detection, but the pumped water would mostly recirculate, rather than going down the drain. Perhaps I don’t have the right perception of the demand pump system, but with no recirc, it appears to be 100% wasted money.

            As for our new recirc line, I’m doing the work myself, so the only cost is the PEX, the connectors, and the insulation. Using the same pump programming, I’m expecting the water heater demand to go down because the cold water and cool water that now flows back to it when the pump is running will be significantly higher in temperature than the current setup, with the same recirculation volume established by the pump, but with a smaller return line that is insulated.

            We are with you on the “behavior modification” front: we’ve also adapted our use pattern to minimize water and electrical consumption, which drive our choices in appliances, use frequency, and use timing, as well as our decision to install the solar array. On the last score, looking at our September consumption and production, despite the unusual number of cloudy days, we produced 97% of what we used, and for August it was 86% (more rainy and cloudy). We’re also planning to pay others to install a radiant barrier on our attic trusses to reduce the extra heat load that has occurred due to switching to Class A fire-rated asphalt shingles from 34 year-old cedar shakes, and to juice the attic insulation from R-30 to about R-50, while simultaneously adding insulation to the attic duct work (and on top of the new insulated recirculation PEX line).

          2. @Marty, the demand pump I’m talking about is operated by a button (hardwired or wireless), not a flow sensor so there’s no water waste. And as I mentioned in a previous comment, demand pumps have a higher flow rate than the typical ecirc pump so the hot water arrives at the remote fixture much faster (depends on pump model & hw pipe volume).

            In the typical retrofit scenario, the pump gets installed at furthest fixture (under the counter) and the cold water line is used for the return. Of course, a dedicated return line can be used if available. A differential temperature sensor shuts down the pump when hot water arrives at the fixture. Typically, the distribution line passes other fixtures en route so a single pump can serve multiple fixtures, in which case you can have multiple activation buttons.

            Here are two demand pump systems: Chilipepper, ACT D’MAND.

  15. I want to do this, but I’m trying to figure out ducting. I have a big 2-story house in the Boston area, very tight and well-insulated, with a large (1600 SF) open-plan unfinished basement that is within the insulation envelope. I spend most of my time in the basement, working in my workshop. I don’t want it to get too cold. Right now, the basement heat and AC zone never runs, because the space stays around 70 -72F year-round with no conditioning. Of couse, some conditioned air is being drawn down into there, because I made no attempt to separate the basement and first floor thermally (no air sealing and no insulation between them), and there is a return-air register in the basement with no zone damper on it (always open). I think there is almost no heat loss or gain from or to the basement from the outside, because there are only 4 small double-pane windows, and the walls and slab are extremely well insulated. Paradoxically, it’s the summertime when the basement is almost too cold, because it’s 72 (upstairs is conditioned to a constant 77) and I’m dressed for summer and my body is acclimated to warmth. So, in summer, should I duct the cold air output into the return air of the HVAC system, with a damper to dump it into the basement in winter? I’d like to dump it outside in winter, but then I’d have to bring in cold outside air for make-up air, defeating the purpose. Right? I have a Zender ERV, but don’t think that helps answer this question. Do you think maybe a heat pump water heater in the basement won’t affect my comfort much even if I don’t duct it in either season, because (a) the basement is so large and (b) we don’t use much DHW during the day when I’m down there? Mostly need DHW in the mornings for showers and there are only 2 of us. I suppose I could just keep a sweater hanging in the basement for my use.

    1. Good idea re: ducting HPWH exhaust to HVAC return. But take care so that the two blowers don’t interfere with one another. To that end, you want to connect the HPWH exhaust duct as far from the HVAC blower as possible, where return side static pressure is lowest. If the exhaust air makes the basement uncomfortable for you in winter, you could strategically use the damper to route the cool air to the HVAC return while working in the basement, or temporarily turn the unit off (assuming that doesn’t interfere with HW calls).

  16. Personally, I would not overthink it too much. The unit doesn’t run so much in my conditioned crawlspace to effect the temperature in any appreciable way, nor does it dehumidify all that much. I have an adjoining conditioned basement that is sealed from the crawlspace and the temp and humidity differences are not that different regardless of season.

    I would get the unit, try it out, and, if you need to, handle the ducting later.

  17. Is it true that there are only 2 brands of packaged HPWH available in the U.S. right now? Is there any advantage or disadvantage to choosing the other brand, A. O. Smith?

        1. I never hear mine in the crawlspace when I am in the house and it has been pretty quiet when I am down there.

        2. I called Rheem and asked if they would replace or repair it if I bought one and it turned out to be noisier than their specs say it will be. They said yes. They said they had had a problem with a batch of noisy ones and had fixed them under warranty. If you download a decibel measuring app for your smartphone, you can find something in your house that is about as noisy and experience what that decibel level sounds like. It is pretty quiet.

    1. We rented a house while on a family trip which was probably built between 2005 and 2010, so I assume that the water heater was the original. It had the AO Smith HPWH in the garage, and we were very happy not to have somewhere inside the house. Very noisy. As a result, when we bought ours, I avoided the brand, and went with the Rheem which had numerous reviews and technical data suggesting that it was fairly quiet. It does emanate sound, but it is not raucous and is not heard anywhere within the house unless you are close to that area and intentionally listening for it. I have no issues being in my workshop area (originally a golf cart garage) while it is running, although it can get fairly cool in that space in the winter. We’re converting the space to a hobby area, so I’ll be moving it to the bigger two-car garage. I don’t know if Rheem has further quieted the model since our 2018 purchase.

    2. I just bought a Richmond brand HPWH (from Menards) – it is manufactured by Rheem I believe and branded as Richmond – it was about $500 cheaper than the AO Smith (Lowes) and Rheem (Home Depot). One of the reasons I chose it was that it claims to be noticeably quieter – around 42 decibels. I can’t confirm it this is accurate yet as it is scheduled for install the week of Oct 10.

        1. Tim – you’re correct – I went back and looked at the spec sheet and it is 49 decibels – since it’s made by Rheem it makes sense that it would be the same.

  18. We live in Knoxville TN. The crawl space will be conditioned. He uses ClimateMaster and it does have a hot water heating option. We will have a condensate pump. He recommended the Rheem 80 gallon water heater. Despite his recommendation to heat water with the geothermal system, I was still leaning toward the propane tankless hot water heater until I read your comments. Now I think the heat pump heated water is the way to go.

    1. To my knowledge, ClimateMaster no longer offers a fully variable capacity geo heat pump, instead relying on two stage systems. Applying a two stage heat pump system (whether geo or air source) to a 5 zone duct system is a bad idea. The lower capacity stage of a two stage system is nowhere near low enough to support that many zones. The max number of zones we’ll attempt using two stage equipment is three while paying particular caution to managing excess air flow during small single zone calls.

      Hot water – while it is true that geo heat pumps may be ordered with an optional domestic water heating assist package consisting of a double wall and vented refrigerant desuperheating heat exchanger and a small water circulating pump, it is well advised to consider the total cost of properly installing that option and compare it to the probable savings in water heating energy / cost.

      We used to specify the domestic water heating assist package before the advent of modern high efficiency heat pump water heaters rendered them cost ineffective:

      Properly deploying the assist package so that it actually recovers and stores useful amounts of heat in the form of warmed water requires connecting the assist package domestic water lines to a dedicated preheat tank upstream of the primary water heater. The assist package can’t totally replace conventional domestic water heating since its effectiveness and capacity depends on HVAC loads – during times of year when heating / cooling loads are low there is not enough heat recovery to meet domestic needs.

      The cost of a proper domestic hot water assist package installation likely approaches $3k in many / most markets, and its heat recovery can be expected to supplant only 50-60% of total domestic water heating demand / cost. Since current heat pump water heaters can be expected to provide all domestic water heating at an energy cost of about $150, spending $3k up front to potentially save $75 / 100 annually is a bad deal.

  19. Thank you for the article, Allison. It’s getting time to replace our gas-fired water heater, and while I’ve been considering a HPWH, am concerned about noise, as it will be mounted next to my bedroom wall. Your decibel chart is helpful, but do you have any words of caution?

    Your mention of installing a more efficient air filter caught my attention as well. How will you determine what size filter you’ll need to maintain low static pressure?

    1. Our Rheem is rather quiet. Having lived in a house with a gas-fired furnace located in a mechanical space under one part of the master BR, I’d say that the overall noise might be comparable to a gas WH. We could hear the muffled sound of the little fan prior to ignition and the whumph of the gas lighting combined with the continued operation of the fan prior to the air handler starting to pump the air. If your gas WH sounds can be heard in the BR, you will probably find the Rheem to be roughly comparable. But you can either use the on-board program or a timer to turn it off during the night (no reason to keep it on!) and only start up about 30-60 minutes prior to any normal morning activities, such as a shower or washing dishes. The excellent insulation will keep the water in the tank hot overnight, so small uses in the morning would not be an issue. If you have a hot water recirculation system, be sure to have it turn off overnight, also, so as not to waste the water heat.

  20. Trying to fit the heat pump concept into my odd situation… Most of my hot water is from solar thermal, thus “free” (after a serious initial cost). When there is no Sun during serious winter, hot water is a by product of the outdoor wood-fired boiler. But there are in-between periods where I use a propane-fired boiler to top up insufficient solar hot water. If a heat pump is 4X as efficient as the standard gas heater’s ~65%, might it actually be cheaper to burn the propane in the generator and run a heat pump water heater? (Not that I’d actually make that change, but an intriguing thought…)

  21. You would have to look at the efficiency of the generator converting propane to electricity – my off the cuff guess would be just 10-30% depending on generator model and percent load. Then there’s emissions, extra generator wear and maintenance.

  22. So few questions about HPHW and comparison to Natural gas, which may or may not help factor the switch:

    1) What is the cost comparisons of HPHW vs Atmospheric Vent Nat Gas vs Direct Vent Natural Gas?
    2) Longevity of HPHW vs #1 Natural Gas Tank Water Heaters above.
    3) Question #2, when utilizing softener water. I have gone through so many gas atmospheric tanks. Believe primarily due to anode rod being disintegrated from softened water and prob falling apart and corroding tank and or pieces rattling around tanks and causing leaks over time. Are there any issues with HPHW and softened water? Longevity issue that seem to plague Nat Gas Tanks? This question alone could be a main factor in making the switch.

    I am in NJ so have heating and cooling seasons.

  23. Getting back to the sanitization issue, is it necessary to raise the water temperature every day to 140 degrees F? To me, it seems like a waste of energy though I realize you probably don’t have the option of scheduling the higher temperature on intermittent days like every 3rd, day, twice a week, etc. If I’m correct, it would be an interesting option to add as a feature. Thoughts?

  24. I’m not Allison, and I haven’t poked a flow hood in the general direction of my Rheem HPWH, but my educated guess as to air flow through the unit is about 100 CFM. Mine is not ducted, and according to the status screens it always seems to be in low evaporator speed fan mode…my guess is that’s because mine doesn’t have flow restricting ductwork and the space our HPWH lives in never gets much below 70*F.

    My guess is that the controls include an algorithm to bump up the fan speed if airside delta-T exceeds a certain amount or if ambient temp is too chilly…higher fan speed would be a defense against icing the evap coil in a low ambient situation.

  25. A few minutes browsing yielded no sure answer…my gut guess is that compressor operation is locked out below a certain ambient temperature, possibly 37*F, but don’t hold me to that.

  26. I installed a 50 gallon GE Geospring about 4-5 years ago in our unconditioned basement. I’ve always ran it on heat pump only mode set to 122F and the 2 of us seem to always have hot water. For years it would show up on my Sense energy monitoring app as using about 225 watts when it was actively heating water. Last year, it suddenly changed to about 700 watts. Since Bradford White took over the GE Geospring line, I went to their website which recommended I contact a local service rep. When I did, I explained my situation and the guy was pretty honest with me about how he’s never encountered this, and how if it was still heating water and not showing an error message that there really wasn’t anything he could do to help me. One possible explanation is that the Sense energy monitoring somehow got it wrong. I’m curious if others on here have a general idea how much wattage their units consume while they are actively heating water in heat pump only mode that might have a similar sized tank in a similar environment (unconditioned basement)?

  27. I’m skeptical of both figures…225 Watts seems too low and 700 Watts seems a bit high. Google “GE Geospring hybrid water heater compressor Watts” or similar to unearth a smattering of measurements made in the course of lab studies etc over the years.

    Compressor power is a function of compression ratio or delta P across suction and discharge. The primary factor influencing that is water temperature within the tank; secondary influences are ambient air temperature and air flow volume through evaporator coil (fan speed, filter fouling, coil fouling)

    1. Thanks Curt. Following your suggestion I found this quote in an online forum “According to the GE website, the Geospring HPWH compressor is rated 550 Watts with a rated energy factor of 3.25” Which backs up your claim but is also just a quote I picked up off of a random forum…

  28. I saw similar reference – early models 600 Watt, later models 550 Watt. A rating tends to be worst case conditions – thermostat set as high as it will go accompanied by warm ambient temperature.

    In milder conditions, such as your 122*F setpoint and cool basement, I would expect maybe 2/3 – 3/4 of the rated figure, or about 400-ish Watts

    If you can beg / borrow / steal a clamp ammeter and expose one of the hot legs powering the water heater (probably easiest from within your home’s electric panel if you are comfortable removing it hot). While power factor is an issue, multiplying measured Amps by panel voltage (220-240) should give a ballpark Wattage figure.

    My Rheem checked in at 1.3 Amps during compressor-only operation last I checked so a hair over 300 Watts – consistent with its higher efficiency rating than GE and low thermostat setpoint – (110*F most of the time; a few degrees higher in “winter” (Florida’s short period of comfortably cool weather)

    1. In light of this 300-watt estimate, how warm are we feeling toward Rheem’s claim it “uses less energy than a 100-watt lightbulb?”

      Here’s the fine-print footnote on that bit of puffery:
      ” Based on comparison of the annual operating cost of a 40- and 50-gallon Rheem® ProTerra Hybrid model which assumes the unit is on constantly throughout the year against the energy needed to power a single 100-Watt incandescent light bulb constantly for one year. ”

      Grading on a curve, I’d give it a B+

    2. @James wrote: “Grading on a curve, I’d give it a B+”

      Nice… a favorable grade, but only because everyone else’s puffery is worse!

      I just checked the 40 gal ProTerra EnergyGuide label and it indicates 866 kWh/yr, which is indeed less than the 876 kWh (nominal) required to power a 100W incandescent bulb. So the comparison is true enough, but is the 3.65 energy factor (as shown on the label) realistic?

      As an aside, I noticed baseline hot water consumption for the ProTerra label is about 16% less than for a conventional electric water heater. I wonder why that is?

      866 kWh/yr x 0.03414 therms/kWh x 3.65 UEF = 108 therms/yr
      3493 kWh/yr x 0.03414 therms/kWh / 0.93 UEF = 128 therms/yr

  29. I am confused by your multiplier/divisor at the end. If you multiply both, you get 111 for the second, making them comparable,

    1. Yup, you caught me asleep at the wheel! I’m accustomed to working the other direction (from therms-of-load to consumption) for furnaces and other appliances with a fractional energy factor that I divided by rote. Please ignore last half of my post.

  30. This has been a great conversation. I believe heat pump water heaters are going to be huge. I am looking at de-carbonizing and energy efficiency and this looks to be a prime contender. My questions about longevity are based on the fact that in my current iteration, I am dealing with commercial and institutional clients who need to have at least a reasonable idea about service life. I am going to eventually turn this over to the younger and much brighter minds in our Firm to do further research, so any sources of information are valued right now. Please feel free to forward credible details and educated opinions.

    Roy Collver

    1. Roy, one consideration regarding the heat pump water heater vs. electric is the maintenance on the latter due to the high surface temperatures, when using unsoftened water. Scale is created that reduces the efficiency of the elements, and also tends to result in anode corrosion, both of which must be replaced periodically to maintain performance and avoid tank erosion. Gas water heaters also can require anode replacement, as well as issues with corrosion of the exterior surface where the flame is applied to the tank (which can result in leaks and thus system failure), and corrosion of the gas vent system. In addition, inadequate venting can lead to excessive carbon monoxide.

      With the heat pump system, the operational temperatures for the heat exchange are much lower and thus tend to have a much lower impact on the materials. On the other hand, the heat pump system itself is more complicated than the simple electric or gas heaters, so there are more opportunities for something to fail or lose control. However, one can note that whole-house heat pump systems that do not have any leaks in the refrigerant lines or radiators can last for 15 or 20 years with minimal maintenance. While there are no guarantees, it would be reasonable to expect a “standard” heat pump water heater to substantially outlive a “standard” electric or gas water heater, and probably with significantly less maintenance required.

  31. I am soon to install a Rheem HPWH to replace my old gas model but need advice as to tank size and whether to select 15 or 30 amp for most efficient and least costly use. We are usually only 2 in a 3400 sq ft California home but during holidays may number 5-6. I hope to run it on heat pump only mode to avoid use of the resistance backup heater. 2 daily showers are the primary draw.

    If true there is now a 120 volt version the lower voltage is really attractive as our electric panel is about maxed out – but does that carry with it a performance hit that’ll be problematic?

    Suggestions welcome.

    Thank you – Larry

  32. It is my understanding that the 120V model is heat pump only, while the 240V has heating elements.

    We have a 65 gallon 240V model. There are usually two of us in our home, but that can balloon to 8 at times. That said, we have only run out of hot water while in HP only mode when we fill our jetted tub. Since we only use that a few times a year, it is no big deal.

    If you do use tubs or have high usage, then you might want to go to the 80 gallon model, but we find the 65 more than adequate. If you do not have room in your panel and want to play it safe, get the 80.

  33. With only 2 people in my house and a cold climate, wasn’t worth it in my case.
    In addition, there are a lot of complaints about Gen 5 of the product on FB HVAC blogs. Sounds like you’re lucky you have a 4.

  34. While I understand the desire to switch to non-fossil across the board you are seriously biasing the energy cost comparison by quoting only the VERY high fee gas supply in Atlanta (made worse in the summer by annual averaging). A gas heater uses very few therms of energy and in any normal gas provider cost plan the comparison would be gas lopsided. You should include the therms/KW comparison to provide information for people who do not have the “paid for” Georgia regulators.
    However, a more important question: why didn’t you use a solar water heater (concentrating version), or at least one to feed your electric heater?
    The scare tactic of CO is also a bit over the top … don’t you have a CO alarm? Or better yet, a properly installed vent?

  35. We are in northern Illinois. Three or four years ago we installed a 50gal Richmond/Rheem Hybrid HPWH in the unheated and not yet insulated basement of the hundred year old home that we are upgrading in a several year process. We use it only in heatpump mode (117°F) and duct it from the main level general living space, through the room air vent of our little glass front woodburner. We vent its dry air out into the basement, and the open stairwell, via our entry foyer, serves as the return. Our biggest hot water usage is our regular Sunday evening soaks in our large two person tub. So, during the six months of the year that define our heating season, before tub time, we usually throw a few sticks into the woodburner to supply the HPWH with as high as 140°F air (usually around 110°). The cold basement temperatures take a small toll in tank heat loss, so I have occasionally contemplated an additional insulation wrap, but not enough to have even done a quick calculation, We bought our HPWH back in (IIRC) 2017. We gave up on the phone app, which was continually malfunctioning and needing upgrades. Perhaps they have gotten them more dependable since then. We had trouble with a condensation sensor. which shuts off the heatpump, turns on the fan, and starts an annoying beeping alarm. Rheem said it was an issue they had with an early circuit board and they sent a new one, for us to install All in all, we are pleased with the Rheem, especially its ability to use ducting. We probably are spending not much moree than $25 per year for heating our water (two person household) with electricity from a local Community Solar farm. I have a couple of salvaged water heater tanks and glass and insulation, that I had planned to use for a passive solar water preheater in the sunroom that we hope to build in 2023, but with the efficiency of our HPWH it will be a folly that can never save enough to be cost effective. I just want to demonstrate how to build a simple freeze-proof one for a northern climate. We haven’t used any fossil fuel (gas) in our hundred year old house for the past three years. They were quite confused and suspicious when we disconnected. They even sent a crew out to install a new meter. It continues to read “00000” We have also been driving electric for five years. Our energy efficiency upgrades continue. I am enjoying finally doing a house for myself ;O)

    Larry…As for 15amp or 30, we had limited electric service capacity. So, when we bought the 30amp HPWH, as the only version Menards offered, I ordered and installed the smaller (15amp) resistance elements, to retain electrical capacity for our minisplit heat heat pump, without having to upgrade our whole electric service. But, if you have the room for 30amp, might as well have the capacity for faster heating. Either way, it will still require the same amount of energy to heat your water.

    Laren Corie
    Designer of Passive Solar
    and Energy Efficient Homes
    Since 1975 (retired)

  36. Any thoughts on a simple damper and removable cap integrated into a “t” which one could manipulate to harvest and or exhaust the vented air?

  37. Ah, yes solar electricity for the heater and a solar collector to at least preheat the water … although at $25 per year maybe skip the preheat as you mention regarding the someday sunroom.
    Which brings me to the real problem in Allison’s installation – Georgia Power, one of the dirtiest utilities in the nation. No CO indoors but plenty of CO2 /sulfur in the outdoor air. Perhaps I should mention that depending on where he is in the Atlanta area he could be getting hydro power locally or from the TVA in North Georgia and Tennessee.
    Need to look at the whole supply chain to know if a gas WH is less overall pollution than an electric one feed by a coal using utility.
    Obviously your own or community solar is the best choice.

    1. Tom, yes, Georgia Power is one of the dirtiest electricity producers in the nation. And one of the most profligate with ratepayer money as well, with the full support of the Georgia PSC. I do buy Renewable Energy Certificates (RECs) each month to cover my electricity consumption and will invest in Community Solar soon. When it’s time to put a new roof on the house within 5 years, I hope that the GA PSC will have removed the ridiculous cap on net metering in Georgia.

  38. I have the 65 gal. version of the Rheem [XE65T10HD50U1] and I too dislike that when running in heat-pump only mode, the app tell me to switch to the “economy” mode that uses the heating elements!
    Has anyone investigated the anode rod replacement on these units? Looks like you may have to take off the top cover that surrounds the heat pump to access the rod?!? Just curious if anyone has replaced theirs yet?

    1. We have had our 80 gal version for about 2 years now (in a passive house). Monthly electricity consumption is at about 60 kWh for a family of 3, keeping the tank at 110F (with a scheduled heating up to 140F once a week per above suggestions).

      Would love to know how to check and replace the anode as well since our water tends to be medium hard and I imagine we need to replace the anode soon to extend tank life.

      1. @Marek, a number of factors affect anode deterioration, but in general, soft, low-pH (acidic) water is more likely to cause premature anode corrosion. Hard water has its own problems but I never associated that with anode corrosion.
        Here’s a very helpful discussion in Terry Love’s plumbing forum on how to access and remove the anode rod in Rheem’s hybrid water heaters. Oddly, there’s nothing in the Use & Care / Installation manual on where it’s located or how to access! Thank goodness for online forums 🙂

        1. Marek, you can also find videos on Youtube of how to change the anode rod. It starts by removing the wiring from the top and anything else that might prevent you from removing the lid, like a duct on the intake. The anode rod is then down at the top of the tank, which makes removing it more awkward than for a regular water heater. You also may need to cut the rod in two pieces to get it out if you don’t have enough ceiling height.

        2. Thank you David and Allison! Indeed, the discussion on Terry Love’s plumbing forum is supremely informative, and there are a few Youtube videos with step-by-step visual instructions (e.g., https://www.youtube.com/watch?v=akee2Hvkfu8). It certainly seems like a more complicated process than replacing the anode in a gas water heater which I’ve done myself. I guess because you have to remove the top cover and then disconnect the electrical wiring Rheem didn’t explain how to replace the anode in their manual.

          1. I imagine Rheem does not consider anode replacement to be a homeowner DIY item and wants you to call in a licensed plumber. There ARE a number of things that can go seriously sideways if you don’t know what you are doing. Just removing the existing one can be a challenge. There is a special wrench made with a striking surface on the end that you smack with a 2 or 3 pound club hammer just to break the grip on the threads. Not a job for the faint of heart, but doable if you have a reasonable mechanical aptitude.

  39. This might be a dumb question, but would it makes sense to put a vent behind a refrigerator so the cold air ouput from the heat pump blows on the refrigerator condenser and then put a vent near a homes stove/oven for the warm air intake to try to capture some of the waste heat from cooking? Would this make the refrigerator more efficient too?

  40. Maybe in theory, but as a practical matter there are codes mandating distances between exhaust and intakes, and certain discharge air streams (such as those from cooking, combustion, and clothes dryers) are too contaminated / fouled to risk reuse.

    Exhaust from a heat pump water heater aimed at the coil of a nearby refrigerator might make a small improvement in the refrigerator’s energy usage, but those two appliances are rarely installed near each other, save for the odd 2nd fridge / freezer in a garage or basement.

  41. Not a dumb question at all. The issue with this solution is that the runtimes of each of the appliances does not normally line up. A HPWH does not run very long, nor do ranges or fridges. It would be better to tap a more constant heat source (say a furnace in a crawlspace that give off residual heat).

  42. It is excruciating, if you are an energy-saving geek and you can see by-product heat or cold just going to waste. Trying to connect the dots in a practical, cost-effective way can be seriously frustrating.

    BUT – keep thinking about it, keep asking these kinds of questions in this type of forum. There are no dumb questions. We need all hands on-deck to try and work through our current problems.

    1. A long long time ago in an energy saving galaxy far far away there was an initiative to actively heat domestic water using waste heat from a typical residential refrigerator using a refrigerant to water heat exchanger.
      If memory serves, the device was capable of heating 15-20 gallons of water per day, but proved unready for prime time for several reasons related to constructability and safety.

      I have personal experience with installations that recover waste heat from a central AC system for domestic water, but that’s also an idea whose time has come…and gone.

  43. The pics of the HP water heater and app look exactly like the Rheem Hybrid HP unit I installed last weekend.
    The rebates paid $800 of the $849 cost from Home Depot. The DOE label on my old electric said $594 operation cost per year, and the DOE label for the Rheem HP, says $104!
    We don’t have a gas option (natural or propane) so electrical was our only option…but gladly so.

    1. Phil, how did you find one for $849 at Home Depot? Mine says $1600 for the smallest model.

  44. Tim, local energy utility conservation programs often buy down the cost new EE tech to encourage adoption and help them meet growing demand through conservation vs building new power plants. And it works. Here in OR our energy consumption has stayed relatively flat since the 90’s despite a growing population.

  45. My water heater is in a FL garage, frequently 80-90 F in summer and also 80% humidity sometimes.

    Could a HP water heater make any meaningful reduction in temp or humidity level?

    1. Joel – I can’t quantify the reduction in temp/humidity for a hot garage application, but if I lived in that environment – I would 100% be on-board with a HPWH. I know my North East-location basement is a few degrees cooler with my Rheem HPWH. I would think that it would have an easier time extracting heat from ambient air for you to heat water vs my ~60 deg. basement. They don’t cycle too often (obviously based on your hot water usage) so it may not be a tremendous reduction, but from a electrical savings I would think it would shine here.

    2. It depends on a number of factors.
      -how big is the garage?
      -is the garage insulated in the walls and/or ceiling?
      -is the garage door insulated at all?
      -is the space decently air sealed (finished drywall or open stud bays; does the garage door have a good weather seal)?

      Let’s use the Rheem Heat Pump as an example. The compressor is rated at 4200 btu/h, so it is just over 1/3 of a ton of capacity when running. This is less capacity than a 1/2 ton window air conditioner.

      The short answer is- it depends, mainly on the environment it is in. If the space is a fairly well insulated finished drywall 1 car garage with a 8ft. ceiling, it will probably work to cool & dehumidify the space a bit (Don’t expect 74 degrees @ 50% humidity). It is best to consider cooling/dehumidification as a secondary benefit because it’s operation depends only on when it needs to produce hot water (the cool & drier air is just a byproduct). Will it “improve” the current conditions when running? Probably, but it could be as little as 1-2 degrees and maybe 5% humidity improvement (which is still considered an improvement of your current conditions).

  46. An update to the Rheem heat pump water heater: Rheem used to be the quietest unit on the market for years, but ever since early 2021, Rheem has been having quality control problem with the introduction of generation 5, the noise level has been in 60-70 decibel range. There have been many complaints from customers, and Rheem Hybrid Heater Support has been sending out retrofit kit, but problem continues even if you buy a Rheem unit in Jan. 2022. I have a Rheem ProTerra installed in late December 2021 and today, I am still working with contractor and Rheem trying to get the noise under control. Disappointed to see a reputable company like Rheem with long history of sucess allows a defective product to get into the market and is unable to fix the problem after one full year …

  47. Hi, I am curious about how your heat pump water is working in MN. I live in MN, too. I am wanting to install one to replace a gas water heater. My concerns are about dropping the temp in the basement too much. What kind of drop have you seen? How did it fair in the -20s we had? Any info is much appreciated. Many thanks!

    1. So I hadn’t actually checked the temperature of the basement other than the qualitative going down there and saying “it’s chilly down here”. Your post has encouraged me to come up with some numbers.

      For background, our basement is concrete masonry units (cinder block) without insulation on the exterior or interior. We keep our thermostat at about 64 at night and 67 during the day. There aren’t really any heating ducts that outlet in this space. We keep the temp for the hpwh at 120and it runs in the econo mode. Our electric bill usually come in at 20% below our efficient neighbors per xcel energy and 5% below for gas.

      With the above information, I measured the temp just now, the hpwh had not been running so that gives a baseline temp of about 57 degrees (what the basement is usually at) . The previous night, after it had been running for quite awhile, I measured the temp at about 53 degrees immediately around the hpwh, holding the thermometer in the directly in the cold air exhaust got it to about 45 deg, For us, this is fine, the basement is used as a workout room and storage. I don’t think we’ve ever run out of hot water, or at least I haven’t.

      So mostly, the downside is a chilly basement but it’s always been cold down there, and it certainly feels drier, need a humidistat with data logger to quantitate that. We’re still happy with it, hope that helps.

  48. In my zeal to do my bit against global warming, I added more solar panels, swapped out my A/C outdoor unit for a heat pump, replaced my kitchen stove with an induction electric and my clothes dryer with a Miele heat-pump dryer. I had every intention of also replacing my on-demand water heater with a heat-pump water heater as well, but hit some obstacles that slowed my getting it done. The result was, with every other gas burner in the house shut down, I got an opportunity to observe how much gas was being burned for DHW alone. For two people with a condensing gas on-demand water heater it is trivial! I’m burning a mere 3 or 4 therms a month. My bill is the gas company’s minimum $15. This is certainly de-motivating for continuation of my plan to put in a heat-pump DHW tank. (We do have backup heat for the house by gas, and at a certain low temp the gas burner takes over from the heat pump for heating the house, so actually discontinuing gas service was not on the agenda.)

  49. James, 2 more things to consider: 1) If you don’t have any other gas mechanical systems or appliances you could avoid the monthly service fee that might be doubling your gas bill by going all electric 2) Have you seen any of the info about the little “puffs” of unburned gas that come out of your tankless WH every time it fires up? It’s pretty alarming…

  50. Just a heads up that I have both a Generation 4 and a Generation 5 Rheem Hybrid water heater.
    The increase in noise is unbelieveable between the 4th and 5th Generations.
    Have been hassling with the 5th Generation unit since it was installed the first time in Feb 2021. The warranted second unit this month was just as noisy as the first Over 80 decibels a foot above the intake.
    Over 70 decibels 5 feet in front of the unit.
    Can hear it through my entire house.
    So the fact is absolutely NO….they have not fixed their problems with the 5th Generation units.
    I would buy a 4th Generation over again if I could. It is fantastic in my second/vacation home.
    Wouldn’t touch a 5th Generation with a 20 foot pole if I had to do it over.

  51. I had a Rheem gen 5 hybrid heater installed in garage in Dec 2021 and measured 73 db 6″ from the control panel. I went thru the “fix” process and tried foam & fan retro kit but did not help. Finally had a warranty replacement unit installed last week, and noise level is still the same. because Rheem support was unable to guarantee that new unit is better than the old, I added 2 more layers of 5/8″ dry wall & green glue to existing wall behind the heater just in case problem persists on new unit and was able to reduce the noise to a quieter level I can live with inside the house.

    It’s hard to believe that a reputable company like Rheem with long history of success would not only allow such defective product to get into the market but also continue selling it without any corrective action almost one year after the introduction of gen 5. From what I understand, other brands of heat pump hybrid heater are either equally noisy or worse than Rheem. Sad …

  52. I’m glad I encountered this post! The noise problem is widely reported across multiple forums including multiple reviews on Rheem’s own site. Just last week I recommended these to a new client, but just emailed a follow-up suspending the recommendation until noise issues are properly and permanently addressed.

    This is a major setback, IMO – Rheem led the field on this vital energy conserving technology but seems to have gone astray – sad news!

  53. I installed a 65 gallon Rheem a few weeks ago, in an old midwest basement that hovers between 55-60 degrees, near the furnace which provides a bit of waste heat in the winter. Setting the unit to 121 degree water, I was using 3-7kwh per day. This week I installed an AprilAire to bring the average household humidity from 20% up to around 40%. Since the air reached the target, the Rheem has started using about 11kwh/day. The heat pump is running for much longer periods of time, so I don’t believe resistance heat is kicking in. Could there be that much of a connection between humidity and heat pump performance? Anything else we should check?

    1. Michael: Unless you’re measuring everything, you can’t know if the humidity made the difference. Has your hot water use changed? Has the basement temperature dropped? Has the incoming water temperature dropped? Is your HPWH filter dirty? All of those factors could increase energy use. The easiest way to tell if you humidity makes a difference is to measure the amount of condensate produced. My first guess is that going from 20 to 40 percent RH is not the cause of of the big jump in energy use.

      Also, if you’re basing those energy use numbers on short period of a few days, it could be just the uncertainty in the way the Rheem app shows the data. I think it’s fairly accurate over the course of a month, but it can be wildly off day by day.

    2. I’ll skip a deep dive into the weeds of psychometric and summarize by saying that an increase in ambient humidity from 20 to 40 % by itself should have no effect on an HPWH’s efficiency.

      An increase to 11 kWh per day implies significant usage of resistance heat. Independently verify the 11 kWh, then monitor the unit closely, such as with an AC current meter.

    3. Is the humidifier drawing hot water? Some humidifiers are connected directly to the hot water line, trickle water in front of a fan, and drain whatever water didn’t evaporate into the air duct. That *could* be a rather large new consumer of hot water, causing the water heater to run more.

    4. All else being equal, increasing the relative humidity in the basement will actually *increase* capacity and efficiency (slightly). The evaporator coil will condenser more water and the latent heat from the additional condensation will slightly decrease sensible cooling but the net effect will be to increase the refrigerant temperature (superheat) going back to the compressor and H2O heat exchanger.

      The same thing happens with air source heat pumps — output and efficiency are affected by outdoor air RH (actually, dew point). Mitsubishi is one of the few heat pump manufacturer that account for this in its expanded performance data charts.

      I agree with the other comments: you either have an unrelated short-term variance in DHW consumption, or more likely, the AprilAire is drawing from hot water supply.

    5. Wow, so many things to consider! Understood about the humidity relationship and glad to rule that out. I double-checked and the AprilAire line is pierced on a cold water pipe (same one that feeds the cold side of our basement sink.)

      I’m keeping an eye on showers and will try to gather verified electric usage data (and will force the Rheem into heat pump only mode as well to further isolate.)

      Do those of you who have run these longer have a rough idea of the kWh cost per gallon of 110 or 120 degree water when only the heat pump is used? I haven’t figured out a good way to measure that yet, since the Rheem doesn’t instantly respond to hot water running and I don’t know how quickly hot water cools between uses.

      1. I don’t know how many gallons we have used, but we used 853.18 kWh last year on a 65 gallon Gen 4 Rheem in HP mode only.

      2. Also not sure on how many gallons we used, but a family of 2 adults in HP-only mode, we average about 580 kWh per year; setpoint of 125 deg. on a 65 gal. Rheem Gen 4 unit.

      3. @Michael, 3 months later, I’m curious if your HPWH’s energy consumption remained high?

        The answer to your question about kWh/gallon is complicated. Even if we ignore the impact of backup heat on overall efficiency (which is virtually impossible to predict), the heat pump’s COP depends heavily on ambient temperature and water temperature.

        Even if we could get a table of COP at various ambient and water temperatures, the water temperature entering the heat exchanger (HX) varies widely. That’s because the HX inlet is fed from the tank, not directly from the cold water line (otherwise the heat pump would only operate when there’s a hot water draw). Instead, a circulator pulls water from the bottom of the tank. As the tank warms, the heat pump’s COP drops, so COP is moving target over the course of every cycle!

        That said, we can calculate the kWh per gallon if we make an assumption about the average COP. Here’s the math: It takes 1 BTU to raise the temperature of 1 pound of water by 1 degree F, so it takes 8.34 BTU’s to raise the temperature of 1 gallon of water 1 degree. If the incoming cold water is 55F and the tank is maintained at 120F, the overall delta-T would be 65F, which works out to 542 BTU per gallon (8.34 * 65). Since 1 BTU = 0.293 watt-hours, that works out to 159 watt-hours per gallon. If we assume an average COP of 2.0, we divide 159 by 2 = 79.5 watt-hours per gallon, which works out to 12.6 gallons per kWh.

  54. I have a Rheem ProTerra 50-gallon Gen 5 heater installed recently in Northern CA. With two persons in the house using Energy Saver mode, it averages 5 KWH a day in winter. while I do expect less energy consumption in summer, it’s looks like my heater is still going to consume twice as much as Norman’s gen 4. I plan to switch to HP only and see if it makes any difference. thanks to Norman for sharing the usage data, appreciate it.

    1. John: Northern California (not Canada, right?) is a big area, but it’s likely that your entering water temperature is significantly lower than Norman’s in South Carolina. That’s my first guess at the difference you’re seeing because the Gen5 has a higher rated efficiency than the Gen4.

      1. Allison makes an excellent point. Climate matters, as does the installation location. My unit is in a conditioned crawlspace, essentially the same as my conditioned basement, where the temps seldom are below 60 F in the winter and above 70 F in the summer. It is also within 15′ of all major HW usage and I have a DWHR (drain water heat recovery) device that feeds the HPWH,

        Also usage matters. My wife and I use little hot water other than for showers, dishwashing (manual and machine), hand washing and a way too infrequent soak in the tub. Everything in the house is Energy Star standard or better so water usage is reduced. 2/3 of more of our laundry loads are cold water only.

        Too many variables to draw conclusions, IMHO.

  55. Thank you for comment, Allison. I moved from Charlotte, NC (5 miles from SC border) to Sacramento, CA two years ago, I think winter temperature is about the same before and after the move. Therefore, did not suspect winter temperature as a major factor. However, I did use a recirculating pump on timer which may contribute to additional energy consumption. I plan to monitor the effect of ‘HP only’; if no improvement is observed, I may turn off the recirculating pump and see if it makes any difference.

    1. @John, the recirc pump will certainly increase DHW consumption, even if it only runs a few hours a day on a timer. If you haven’t already read through all the comments, check out my 25 Sept comment, above.

  56. I been using HPHW going over 11 years and I love them! Upgrading to the gen 5 as my old GE Geospring compressor failed and I don’t think the repair cost is worth it in a unit that has had such heavy use with 6 people in the house. It is in our 1st floor laundry and it gives the additional benefit of free extra AC and dehumification of that room which is a huge benefit in Florida. Additional benefit is I run an inverter generator for power backup and having HPHW means that I can have Hot water without overly taxing the generator or burning excessive fuel (really a post hurricane concern) . Planning on some PV given my South facing roof is perfect for it for more energy independence.
    Our neighborhood is electric only so it is the best option (low draw for natural gas given you rarely need to heat here – which is another good thing)

  57. How do you know it’s better for the environment? Do you know the carbon intensity of the mix of electricity coming through the wires, is it lower than natural gas? I’m generally a fan of heat pumps, but gas can be much better for certain applications depending where you live (such as where your electricity supply has high coal baseload, end of long lines where transmission loss is high etc)

  58. First, heat pumps increase the efficiency of electric heating, therefore they also proportionally reduce the adverse climate effects. So, it would be pretty safe to assume that even the dirtiest electricity, through a heat pump, will be cleaner than natural gas. So-called natural gas (mostly methane) is about as severe for greenhouse gas effect as coal. It is true that methane produces far less CO² when burned, but large amounts of methane are released through leakage. That methane is many times more powerful than CO². While it is widely written that methane is only “over 30 times” stronger than CO² over a 100 year period, methane does not last anywhere near that long, so that is a made up number, that makes methane look not nearly as bad as it actually is. Some sources now list a 20 year number of “over 80 times” worse than CO², but again, that does not express its effect in the extremely important next decade. Methane is only in the atmosphere for around 10 years, and during that extremely critical time for us to reduce greenhouse gases, methane is as much as 200 time more potent than CO² (at least 2 x the “more than 80” number for 20 years). It has been found, fairly recently, that methane leakage is several times greater than the fossil fuel industry has been claiming, and is very likely creating even as much greenhouse effect as CO².

    -Laren Corie-

  59. HPWH will produce lower emissions almost everywhere–coal consumption in the US continues to plummet, despite a small rebound in 2021. This site is instructive, it explores that for EVs:
    https://evtool.ucsusa.org/

    We just got our HPWH installed last week, and it’s been fantastic. Given that we have solar, the carbon mix isn’t an issue. Though we ordered it eight months ago, our EV arrived a few weeks ago too, and it’s a little surreal seeing crazy gasoline and methane prices, and thinking it doesn’t touch us at all any more–free fuel for life.

    One thing worth noting about the HPWH, we got the Ruud equivalent to the Rheem, and despite being on the quieter end of the spectrum, it’s pretty loud. It’s in our ground-floor garage so not a huge issue, but we can hear the faint hum on the floor above when it’s quiet. But noise could be a issue if you were installing it in a closet or otherwise in or right near a living space.

    If you’re really curious about the carbon intensity of your electricity, you can find it here:
    https://app.electricitymap.org/map

    Best,
    John

    1. It’s too bad there were some generations (even recent ones) with big problems because that certainly didn’t help their cause. Frankly it turned me against them. At least for my situation where with only 2 people we’ll use barely any power with a small well insulated electric resistance.

  60. Does anybody know anything about the availability of LG’s HPWH? Their press release in 2020 said “The LG Inverter Heat Pump Water Heater will be available in markets throughout Europe and North America beginning in the first quarter of 2021.”

  61. Hi Allison. Hi all. Realize I’m late to the party. Hoping you can help. I’m debating a HPWH. I also have a few years left on my current electric (2014 Rheem). Curious to get thoughts on adding the HPWH upstream & in series with the electric. Then I can keep the HP on a higher temp, add a mixing valve, and effectively get a very large storage with a little heat pump. Am I crazy? Am I just over complicating a WH replacement? Appreciate any constructive feedback!

  62. Hi Brendan,

    I had an arrangement similar to what you describe, though not with a mixing valve back in the early days of HPWH. I think it only makes sense if you have a large household head count or other need for lots of hot water.

    Personally I would not bother with the mixing valve, and I don’t recommend setting the temperature of an HPWH any higher than necessary – its compressor will work much harder owing to elevated discharge pressure arising from high temperatures. High temperatures decrease efficiency, increase scaling and reduce durability of water heaters.

    Consider setting the HPWH no more than 5-10*F above the setting of the electric tank, and the electric tank as low as comfort allows…perhaps 115*F? In my home, wife likes a hotter shower than the rest of us, so that drives our setpoint.

    There is a splinter group in the “what’s the best water heater temperature setpoint?” universe that thinks we’ll all die of Legionnaires disease if our hot water isn’t at least 140*F, but that isn’t main stream thinking, IMO.

    1. @Curt wrote: “I think it only makes sense if you have a large household head count or other need for lots of hot water.”

      And only if there’s an existing storage heater in good condition, as with Brendan’s situation.

      Great point about keeping set points for both tanks as low as possible, which also eliminates the need for a mixing valve. But if the objective is to increase storage capacity and thus eliminate the need for backup heat, it seems like you’d want to disconnect the 2nd tank’s element and circulate the water between the two tanks so the HPWH can pick up 100% of the load.

      Hmm… on second thought, the original tank’s element should only need to pick up its own standby losses, so the savings may not be enough to justify the circulator and associated operating costs. Probably not.

  63. Mixing valves are safety devices required by code in many jurisdictions and just plain common sense to prevent scalding. While some people use them to functionally “increase” the tank size, even lower storage temperature tanks should have them

  64. If you have enough juice – why not? There are a number of ways to handle this depending on what you are after. If it is extra storage – why not set the resistance heater tank slightly higher, put on an ASSE tempering valve and the HPWH becomes a pre-heater to do the heavy lifting from ground water temperature (also can kill Legionella bacteria should that be your desire). Or do it as you suggested and the electric tank becomes extra storage plus back up. Other ideas may occur as well once you start to live with it.

    Whatever you do, jfor fun – Do us all a favor and put an elapsed time clock on the electric resistance tank to help us out with some data as to how often it might be needed. If you really want to get funky, a data logging water meter on the DCW feed and another elapsed timer on the HPWH would really tell the tale.

    I am not being sarcastic here, this would be great info to have. In a better world, there should be grant money available for this kind of data gathering.

    Roy Collver

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