Will a Heat Pump Work in an Old House?
The question of heat pumps in old houses is coming up a lot lately. With the great electrification upon us, heat pumps are quickly becoming the number one choice for space heating. In fact, data from the Air-Conditioning, Heating, and Refrigeration Institute showed that heat pumps outsold furnaces by 10 percent in 2022. Ten years earlier, furnaces outsold heat pumps by 32%. That’s great! But can they work in homes that are poorly insulated and have a lot of air leakage?
A BTU is a BTU
I like to answer this question by saying that a BTU is a BTU. (For the SI folks, a joule is a joule.) Whether it comes from a heat pump, a furnace, or a 20-year old plasma TV, heat is heat. (OK, for the sticklers, let me say, heated air is heated air.) If you’re getting enough heat into the house to match the heat being lost, a heat pump can do the job. For comfort, a heat pump may be even better than a furnace.
As an example, my heat pump did well in our arctic blast a couple of months ago, and it’s undersized. It doesn’t have the capacity to equal the heat loss on those days when the temperature is below our design temperature, so it couldn’t keep the house at our thermosat setpoint. But even with the outdoor low temperature of 7 °F, the lowest it got in the house was 63 °F. (See the article for the data.)
My house was built in 1961 and isn’t what anyone would call a high-performance house. With our encapsulated attic, the air leakage isn’t too bad but wouldn’t meet our code for a new home. For those who want numbers, Georgia code now requires 5 ACH50, and my house is at 8.4 ACH50. Also, our main floor walls do have insulation, but it’s either R-7 or maybe R-11. The basement, however, has no insulation. Our windows are single pane with storm windows. Overall, it’s a mediocre thermal enclosure.
Sizing, equipment selection, and installation are critical
Heat pumps do work in homes with poor thermal enclosures. As stated above, it’s all about delivering the right amount of BTUs. For that, you need to know how much heating load you have. A Manual J heating load calculation is one way to get there. A better way would be monitoring the runtime of the existing system and getting an estimate of how much heat it adds at design conditions.
Then choose the type of heat pump that will get you as close to the heating load as you can without oversizing the cooling side too much. It’s a balancing act, and you may end up oversizing on cooling a bit. But with multi-stage or variable speed equipment, that won’t hurt you so much. If you’re in a cold climate, make sure to get a cold-climate heat pump, like the Mitsubishi models with Hyper-Heat (H2i®).
One thing to watch out for with heat pumps is relying too much on auxiliary heat, especially if that heat comes from electric resistance coils. That can run your electric bill up very quickly. And it’s even worse if you follow the dumb advice sometimes given to homeowners of turning your thermostat to emergency heat when it’s cold outdoors. There are better ways to plan for auxiliary heat.
Then you’ve got to have an installer who can set you up for success by ensuring that the heat from your heat pump will make it into the places where you need it. The duct system is the oft-neglected part of heating and cooling systems, but they’re critical to good performance. The ducts need to be sealed, insulated, and capable of delivering the right amount of air.
But improving the thermal enclosure does help
Having said all that, I’m certainly not advocating for a leaky, poorly insulated enclosure. A robust thermal enclosure does provide distinct advantages. For the homeowner, a better enclosure means you can put in a smaller heat pump, saving money on the upfront costs. It also means you need less heat from the system over the course of a winter, saving money year after year on heating bills.
In addition, the occupants benefit from enhanced comfort. Everyone likes to focus on air temperature, but that’s only one of several factors that affect your comfort. A huge one that doesn’t get talked about enough is mean radiant temperature. With a poor enclosure, the walls, windows, ceilings, and floors can be very chilly on those cold days. A good enclosure brings the temperatures of those surfaces closer to room temperature. And that matters a lot!
Another advantage of a good thermal enclosure is one that accrues to the utility. Smaller heat pumps mean less power needed on those cold mornings or in the evenings when people return home from work. Less power needed for heating can help flatten out both the duck curve and the falcon curve.
The bottom line here is that heat is heat, BTUs are BTUs, and joules are joules. If you have a good unit sized and installed to provide enough heat, heat pumps can work just fine in older homes. Don’t let having an older home stop you from putting in a heat pump. Just be sure to get a good contractor to help you plan for it and get it installed properly.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a popular book on building science. He also writes the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard.
Can a Heat Pump Work in Minnesota?
My Undersized Heat Pump in an Arctic Blast
Heat Pump or Furnace: Which Is Better for Comfort?
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This Post Has 68 Comments
I just completed a full HVAC retrofit of my 1938 freestanding masonry home I purchased several months ago and just moved into. The house had gas fired radiators and no central AC. With the help of my friend and HVAC technician and free design information, I designed and installed a three zone heatpump system. I utilized an existing 1st floor coat closed to hide the 30000 btu air handler and installed ductwork through chases and the 2nd floor joists. I’ve also got a 9000 btu wall head in the finished basement and a 6000 btu wall head in the finished attic. All three run of a single outside Mitsubishi hyperheat unit and a branch box. I’m expecting my first energy bill which will tell the tail. This house has no insulation in the walls and roughly r 21 in the attic. I have been able to stop a lot of drafts, though there’s more to do.
Galen: Where is the house located? How has the heat pump performed so far?
It’s been fabulous. I probably oversized a little, especially the outside unit. The week it was 13° here, it took 3 hours for the heatpump to increase the indoor temperature from 65° (sleep) to 70° (awake). But once it reached 70° it idled back to the lowest fan speed, and stayed that way all day. The high never got above 20° that day.
Heat pump users should be careful with setbacks and in most cases should avoid them or only do a few degrees. The main concern is when the setback is over and the system needs to get back up to temperature most systems will use Aux heat to recover when the difference is high enough (often 3 degrees). If your Aux heat is resistance electric this is going to far outweigh the savings from the setback. Even with a hybrid system (gas, propane, or oil backup) you may lose all the savings of the setback and then some.
Galen you seem to be pretty knowledgeable about your system and maybe don’t have aux heat enabled, but even in that case the system is more efficient when cruising along and not maxing out the heat pump to catch up. Others may know more than me on this part.
I read a lot of comments on other sites about how people hate their heat pumps as they use so much electricity, and I think the use of setbacks is one of the primary culprits. Installers need to do more to educate users how the system works and avoiding Aux heat, or simplify it and say don’t use setback, instead set it and forget it.
Yes and no.
I don’t have backup heat. My system is a Mitsubishi inverter heatpump with hyperheat. So it’s all heatpump all the time.
My old house had a 16 SEER on/off heatpump. I upgraded to a Nest thermostat. The Nest allows the user to determine how much backup heat to mix in with the heatpump generated heat. The thermostat would tell you when backup heat was on, so you could judge your comfort level.
In a leaky house with a low tech heatpump and thermostat, I’d agree with your assessment. Asking for more than 2° will often trigger the toaster wire heat.
Fantastic ? We will see your electricity bill:))
Yes, I’m waiting with baited breath to see the bill. The last bill was $350 but the house was heated with five rented electric space heaters. The upcoming bill should be a better assessment, though the floor refinisher liked to leave the front door open all day …. 😑
I keep reading these articles about how great heat pumps are with a whole lot of anecdotal info about them and how they work well in cold weather. Can somebody actually publish some data? The most important question to me would be some graphical info about what the heat output of the pump is at various outside temps. I’m sure people will say that depends on the manufacturer and type (air to air vs other) but somebody should pick one or two models and plot that data. Or even take a temp data point say 25 degrees which is pretty common winter temp and plot out what the output is over time. The answer is really relevant. If you can consistently get 65-68 degrees out including defrost cycles then that’s great. If though the temperature is only 50-55 degrees that’s a totally different situation and is not practically useable without backup heat and changes the cost/benefit savings significantly.
Greg: It sounds like you missed the article on how well my heat pump performed when our temperature went down to 7 °F. I didn’t measure heat output or supply air temperature (D’oh!), but I do have a plot of the indoor and outdoor temperatures as well as the energy consumption. Here’s the link:
My Undersized Heat Pump in an Arctic Blast
Thanks. I have done a Lot of searching on this topic trying to find this kind of actual data and this is the best and most comprehensive data I have seen. As you know there is a lot of anecdotal info out there about either how great heat pumps are or how terrible they are but this clears up a bunch of my concerns. Back in the day the rule of thumb was that heat pumps (air to air anyways) wouldn’t work below freezing. What changes caused that? Better refrigerants? PWM motors? How does COP come into this if it even does?
Greg, regarding what changed in modern heat pumps, one important change was the switch to Inverter control of the outdoor fan and compressor motor. At first glance, you would not think that being able to vary the speed of the compressor and fan would help that much, though you might understand that slowing down these motors at part load would save energy. But how does that help give MORE heating capacity when it gets very cold out? The key is to understand that inverters vary motor speed downward by reducing the frequency of the AC they are providing. Once you make the investment in the inverter, you can upsize the power components and control it to go to frequencies ABOVE 60 hertz, such as to 120 Hz. Over-speeding the compressor and fan allows it to increase its capacity as the outdoor temperature drops. If you monitor the power drawn you will see it rises quite a bit higher than what is normal at moderate temperatures… as in Double. So yes, the capacity goes up, and the cold-climate models can maintain their rated capacity down to ~5 degrees F, but it doesn’t come easily or cheaply. They gobble up power to do it because they have to work a lot harder, and the motors have stay cool enough to handle that power.
I enjoyed your explanation concerning the inverter compressor to evaporate more pounds of refrigerant and multi speed fan to increase the heat exchange rate across the heat-ex coils. Just the expansion valve got short shrift. The EEV, along with maximizing the heat transfer capability of the coils it provides sufficient cool gas to maintain effective compression ratio across the compressor and to keep that speedy compressor from winding up in the scrap heap.
Since heat pumps move heat from outdoors to indoors, the temperatures are constantly changing. As long as heat is provided above the desired temperature, the heat pump is heating the home even though the air coming out of the outlets feels cool to the touch. In defrost mode, heat pumps are always cool air because defrost mode turns on the cooling cycle. At 47 degrees, heat pumps provide the same amount of heat as they do cooling.
As always, great content.
I recently had a RHEEM HP installed for my 50-yo Wisconsin home. My key takeaway is to make absolutely 100% certain that your HVAC contractor is enthusiastic about the HP technology. I had to drag my 20-year HVAC contractor to do the install and it has not gone well mostly due to their lack of knowledge about best practices.
I am hopeful that the Inflation Reduction Act incentives will convince more in the HVAC trades to learn about and support the technology, but my experience has been that “the way we’ve always done it” mindset is alive and well and resistant to change.
Kevin: Yes, having your contractor on board is extremely helpful, if not essential. I can’t tell you how many times I’ve heard people say they wanted a heat pump but their contractor talked/scared them out of it. There are some really good contractors who understand the technology and know how to do it right. There are many more who don’t.
“Everyone likes to focus on air temperature, but that’s only one of several factors that affect your comfort. A huge one that doesn’t get talked about enough is mean radiant temperature. ”
Any advice on thermostat strategies for optimizing mean radiant temperature?
Ted: Optimizing mean radiant temperature comes from improving the building enclosure, not manipulating the thermostat. Reduce air leakage and improve insulation to increase the mean radiant temperature in winter, and you can lower the thermostat setpoint. In the airtight SIP house I built 20 years ago, the interior surfaces were warm enough that I could keep the thermostat set at about 65 °F, seven degrees lower than I keep it in my 61 year old house.
Given a good enclosure, does a setback strategy help or hurt MRT? Is it better to keep it constant?
In an average or poor enclosure, can HVAC equipment selection improve MRT?
Setback will hurt MRT as everything in the house will be cooler for a while until it catches up to air temperature, ie interior walls, floors, furniture. If the air is 70 and the interior mass is 65 (the outside walls will be colder still) you will feel colder than if the interior stuff is 70.
Setback with heat pumps has other dangers and negatives as I talked about in a comment above.
My ASHP experience supports your statement with this tweak: “Optimizing mean radiant temperature comes from improving the building enclosure AND not manipulating the thermostat.”
My house was built in 1963 and I now heat my house with heat pumps. Before installing heat pumps I did a lot of work on the house. I blew in 17″ of cellulose in the attic, added R-5 under my new siding with R-11 FG (at best) in my walls. I had changed all my windows over the past 15 years. I have HDSF in my rim joist with no other insulation in my unfinished basement.
I did as much air sealing as possible which came out to between 9-10 ACH. I decommissioned my 22 year old oil boiler with a tankless coil with 2 zones (1 on each floor). I replaced my old ducted C/A system on the 1st floor with a HP and then I added a Mini-split 3 zone ceiling mount system for my 2nd floor. In place of my oil fired tankless coil I installed a 50 gal HP DHW. Just before I replaced these systems I installed a 14.2KW solar array on my roof that produced 16.2KW this last year. I haven’t had any utility cost in the last two years.
This past month it went down to 2 deg. for 1.5 days. My inside ambient went down to 64 deg. I turned on my fireplace that has a resistance heater in my family room and a small resistance portable heater in my kitchen (the 2 largest rooms in the house). The rest of the house was fine at 68 deg.
Thank you Mother SUN!!!!!
Rich: Sounds like you make some nice improvements to the enclosure and are enjoying the benefits.
I have had both heat pumps and furnaces and a common issue is getting them sized correctly. They have all been over sized even when I had the data to back up what I wanted. The furnace I was able to change some settings so it only ran about 60% of capacity so worked well and saved $.
The challenge now is how to do that with the current heat pump.
I suspect that old homes won’t have issues as the systems will be oversized from the start.
John: Oversizing happens even when you’re trying to size below the load. That’s certainly the case with my house.
We need electrification urgently but as you allude “The duct system is the oft-neglected part of [especially existing] heating and cooling systems, but they’re critical to good performance.” I worry in these early days that some people may get inferior systems installed.
In speaking with a local program manager that’s pushing ASHP conversions of existing buildings in cold Ontario, Canada, I asked if the HVAC company he recommended did a design heat load calculation; they hadn’t*. Upon digging deeper into the discussion, I asked if the existing heating system was adequate (my neighbour has the same size, vintage of 1913ish double brick as my house) as it seemed “low” compared to mine or at least on the cusp of just squeaking under the wire if they upgraded the enclosure. He said:
“The contractor said the existing [small] duct work in the house was limited to xCFM of total flow at a given speed and therefore, back-calculated that it could only handle a specific air handler size pegged at a heat capacity of 35,000BTU.”
Luckily the inside and outside units are matched per AHRI and it’s cold climate rated according to NEEP.
How can “the Great Transition” avoid this potential black eye going forward?
* I confirmed with the client who didn’t have the Manual J report. She said the only thing he asked for was the square footage of the house. ie, he did the rule of thumb sizing.
Greg: Yes, this can be a big problem. Jim Bergmann discussed it in his open letter (link below) better than I can in this comment.
Allison, in that photo of your attic insulation, I notice you’ve added some 2x8s (?) to the outermost couple of feet of your roof rafters. Can you explain the purpose of that?
Barbara: That’s not my house. I believe that’s a Habitat for Humanity house that we do pro bono energy ratings for. But I think what you’re seeing there is extra lumber in the trusses because they’re probably energy trusses, also called raised heel trusses. More on that here:
The Low Spark of Raised-Heel Trusses
Older home retrofits may have issues with cooling: sweating in ducts with the slow moving cold air? I have a 1970 home that originally was heat only and AC was added later circa late 70s. Concerned here with some ducts with no access to insulate them with slow cold air and sweating. Too risky to use a variable heat pump?
I was able to locate all the ductwork for my retrofit within the conditioned space of my home. There’s only a couple of degrees difference between the return air temperature and humidity and the room air temperature and humidity.
If you added C/A on an existing furnace then your ducts are probably too small and it will affect your system as well as it’s efficiency
Right on the money about a Btu being a Btu. I get so tired of hearing other old timers (as I too am an old timer) claiming heat pumps are as good as whatever they believe is better. I’m still a fan of gas heat and even oil heat if that’s what is already in the house, but heat pumps are greatly under appreciated. Thanks for a great article, Allison. Now I can show more support when this comes up.
Concur that installation is critical. Unfortunately, it is almost impossible to find a company capable of diagnosing issues on a mini split – they are MUCH more complex than standard run of the mill gas furnaces. Even Mitsubishi Diamond status seems meaningless…
If the manufacturers want to sell these things, they need to significantly up their training and certification game. Training one person at a company and giving that company Mitsubishi Diamond does everyone a disservice.
I can’t agree with you more Cal. Another problem though is who is willing to pay for a proper job. Unfortunately no one wants to explain it to their customers
The basic refrigeration cycle is still the same. The best training for ductless systems comes from the manufacturers of those systems. We need to adjust our thinking when addressing issues with ductless systems, and all current inverter technologies. It’s a matter of keeping up or dropping out. Once ductless systems are understood, they are no more difficult to diagnose.
I am a fan of the (few) air-to-water monoblock heat pumps for the simplicity and back up heat they usually incorporate in the indoor buffer tank. The outdoor unit is sealed with refrigerant in the factory and they could use even flammable natural refrigerants with low GWP, but the only ones now available use R-410a or R-32 with relatively high GWPs (2085 & 750 times worse than CO2). They pump warm glycol mix through a coil in an indoor storage tank. If they fail in 20F weather the service person doesn’t have to spend 4 hours in the snow to find the leak, fix it, evacuate the air and recharge. They can remove it and work fix it in a shop. Meanwhile the back up resistance coil in the hot water tank can keep the home warm. Or they could be swapped for a spare unit. That would be a nice electric utility service offering. The downside is that they only make ~120 F hot water, which is not hot enough to recover from a substantial night setback. But they can also make domestic hot water. They work fine with room fan-coils similar to mini-split heads, but they will not recover from night setback with existing baseboard finned tube radiation. But CO2 refrigerant versions are coming that will heat to 170F, so stay tuned.
In addition they don’t have to be installed by a refrigerant tech, which we are short of. Any plumber can install it. It’s just PEX water piping. Or with a high-temp version, just use your existing heat distribution system. Add a few fan-coils for cooling and dehumidfying.
Why don’t I hear more on air to water heat pumps. All I read is mini splits and duct work. In Europe, they use it all over. I would think it is easier to replace your old boiler with an air to water heatpump without major construction. Maybe you can tell us more about air to water heat pumps.
As always, great post, Allison. Thank you for addressing this.
You’re welcome, Stacy. As you might suspect, your post last week brought this topic to mind for me, but that certainly wasn’t the only thing that spurred me to write this.
The issue with a heatpump is that it has down times when its on a defrost cycle, on a well insulated house you might not even realize that, but on unisulated room on a cold day while on defrost the room tempature can fall and not come backup before the next defrost cycle kicks in
There is an issue with a mini-split or any heat pump with a low-temperature supply medium: They don’t recover quickly from an 8 or 10 F night setback. I have a condensing boiler with baseboard finned-tube radiation and a few weeks ago I tested this by adjusting the reset schedule so that it stayed in the 120-130 F range. I found that it could maintain space temperature at 30 F outdoors, but took 7 or 8 hours to recover from an 8 F night setback. So the makers of mini-splits say don’t use night setback, or don’t setback more than 2-3 F if you must for sleeping comfort.
But consider the impact on the annual heating load of the home. The heat pump doesn’t just have to replace the Btu’s that the original boiler was providing, it faces a larger heat load. Annual heating load is often calculated using the deg-days below 65 F base temperature. But if you have night setback, you calculate the daytime degree-hours at 65 F base plus the night-time degree-hours at a 58 or 60 F base temperature. And there are FEWER degree-hours for the lower base temp, so night setback has a reduced heat load annually than no setback.
Hence a heat pump in New England costs more to operate than gas heat because (a) the cost per Btu is higher for the heat pump than the gas, but in addition to that issue (b) without night setback the heat pump must deliver more Btus annually. Unfortunately, although heat pumps are the only practical way to decarbonize our homes (and yes they are more efficient than combustion), they will cost MORE to operate than gas heat, and savings won’t be huge compared to oil.
So how are we going to motivate this conversion process if we are honest about operating cost? The US-DOE has come out with a new heat pump performance rating called HSPF2 that is lower by 30% than the old HSPF numbers (single zone mini-splits that had a 13 HSPF are now 11 HSPF2. Multi-zone mini-splits that were 10.3 HSPF are now 8.8). The HSPF2 can be used to more accurately calculate the electric use for a given annual heating BTUs needed, and these lower numbers tell you that they actually make fewer Btus per kWh than the old HSPF predicted. I do see the issue of higher operating cost vs gas mentioned in some articles, but no one mentions the added cost of the larger heating load due to no night setback.
The incentive payments in the IRA law will be necessary to help people convert, and air-to-water heat pump conversions should cost less by re-using the old distribution system, but unless they can make hotter water, they cannot recover from night setback either, so higher operating cost is still a problem.
How do we convince people to do an expensive conversion that will have higher operating cost? Will the addition of cooling be enough to convince them? People get solar because they can lock in 25 years of savings that will exceed the cost of installation. I don’t think heat pumps in cold climates deliver savings unless you are using a very expensive fuel now. Will people convert to save the planet for their grandkids? Some may, but not enough, I fear.
Sorry HSPF2 is 15% smaller than the older HSPF (not 30%). The calculated HSPF2’s were above were for 15% reduction due to the more real-world test procedure, which gives more accurate operating costs. SEER2 is also smaller for cooling calculations, but only by 5%.
So far I’ve only read a small portion of your comment, but I don’t know how you got the notion that a HP has a higher annual heat load than a gas boiler????? If I’m not mistaken the annual heat load (following the laws of physics) have to be the same.
Where did I go wrong?
Richard, I presume that if you have read the rest of my comment you know why the heat load increases if you don’t do night setback. The whole reason we do night setback is to Reduce the annual heat load. If we have to give it up with heat pumps we will have larger heating loads.
I think there may be less confusion if you referred to “annual energy usage” rather than “annual heat load”. The term “load” in the field is universally associated with power, while “usage” relates to energy.
Perhaps you are right Robert. In my 30+ years of Consulting Engineering, a heat load was a calculation of the heat lost by the structure at the design outdoor temperature. If you do the calculation using degree-hours for your climate, you can calculate the annual heat loss. And if you setback the building temperatures for part of the day then the degree-hours get broken into two segments: those at normal indoor temperature and those at setback temperature. We use “load” in the sense of the work that the heating system has to do to maintain building temperatures. That may be common in engineering circles, but maybe not so common in general usage. Thanks, I will try to remember.
LOL, there are numerous comments on this blog that are rather technical, but rarely would they require more than a couple of minutes to read. If you want to understand someone’s position, reading their comment in its entirety would be a good first step, especially before risking embarrassment by erroneously suggesting that there is something fundamentally wrong with their thought process.
Alison points out that “A BTU IS A BTU” no matter how you supply it. After thinking about this for a week or so, I have concluded MAYBE NOT. As I outlined in my previous comment, if we cannot do the large night setback we have been using with our boiler when we convert to a heat pump (because recovery is too slow), we now have to supply more BTUs for all those cold winter nights (when our when our heat pump has lower COP than it does in the warmer daytime hours). So we are asking for more BTUs under harder operating conditions where COPs are lower . If that isn’t bad enough, beginning this year DOE changed the heat pump rating system to give more accurate operating cost estimates. The new HSPF2 (heating system performance factor- version 2, in kBTUs-out/kWh-in) are 15% lower than the old numbers we have been using. If you get operating cost estimates based on the old HSPF, add 15%. We could avoid some of these problems If we had air-to-water heat pumps that could make 170 F hot water. We could maintain the night setback for fewer total annual BTUs and reduce cold night operating hours when COPs are lower. We still have to live with higher electric fuel costs in some areas and the more realistic, lower 2023 efficiency factors. To me, the question seems to be not whether heat pumps can supply the BTUs we need, even in the coldest weather, but can it supply them affordably on a seasonal basis? The answer I am getting in the cold northeast seems to be “not yet”. But ask me again at the end of this winter when I will have some final natural gas prices.
After switching my primary system from oil-fired hydronic baseboard to ducted ASHP, I abandoned nightly setbacks due to poor recovery, but the slight increase in energy consumption (over ASHP with setbacks, which still beat oil by a factor of at least two) was considerably less than the tremendous increase in comfort (air temperature vs. “mean radiant temperature of the surfaces”).
I haven’t run the numbers, but a residential HPWH (typically up to 80 gallons and 140°F) might store enough energy to augment low-COP setback recovery meaningfully.
Jim, When posting cost comparisons between systems and fuels it’s really important that readers know what region you are talking about. I live in southern New England where oil costs a bit over $4.00 a gallon lately. I am buying electricity for $0.26 / kWh. An air source heat pump with an HSPF2= 8.8 (formerly it was the old HSPF=10.3, but that was over-optimistic), an oil heating system would cost about 13% more than the air source heat pump, so it is a long way from double the cost of the heat pump. Moreover the oil baseboard would give me a warm curtain of heat at the perimeter of every room (even small rooms like bath rooms where the heat pump does not reach). As it is I have a gas condensing boiler and we pay $1.94 /ccf for fuel, so the heat pump would cost 42% more than the gas (~$500/year). So as you see local prices matter, a lot.
BTW, those numbers for the heat pump are for just replacing the BTUs that I use now to heat with gas. But I set back 8 degrees at night on the first floor and for about 18 hours/ day on the second floor. But as you say, I would have to give up those setbacks with a heat pump, because it would not recover from the setback temperature in a reasonable time (I know… I have tried). So the 13% theoretical savings versus an oil system may disappear if I have to supply MORE BTUs with the heat pump because it has to maintain comfort conditions 24 hours a day. My conclusion is that air source heat pumps will not save money in the New England region at current fuel prices, perhaps not even for oil heated homes. Propane heated homes would have significant savings at $3.80 / gallon, but I don’t think many homes are heating that way in our region. Please, let’s all mention what region we are talking about when comparing fuel prices.
I live in Long Island NY. My friends that have oil here are probably paying about the same as you. My electric cost here is $.22 . In the past I was getting at least 300 gallons a month during the winter months, and that was only for heat and DHW.
I switched to heat pumps two years ago and I calculated that my electric cost, which also includes the electric use in the rest of my house, is around $350. a month.
Gene: I provided that information and my cost analysis in the aforementioned discussion:
Don’t expect to get the same feeling of comfort from an air handler type heat pump as that from a mini-split. The cfm delivery of frequently 80 degree air from the air handler creates an uncomfortable environment in the home.
Hopefully the new systems attaching an air handler to an an inverter outdoor unit will yield warmer delivered air temperatures.
My 2.5 ton Mitsubishi air handler with ductwork in the conditioned space delivers heated air at 101° F at the register vs my 9000 btu wall head that delivers heated air at 93°. The 6000 btu wall head delivers heated air at 86° but it’s coolant lines are 45′ long. All three run off of a 48,000 btu outside compressor with hyperheat and through a branch box.
Mike, you make a good point about the EEV being an important part of the low temperature performance enhancement too. In writing my explanation, I got caught up thinking about the motors. It occurred to me that with bigger power output components the inverters can supply more power as they go above 60 Hz and speed up the motors, but what about the MOTOR size? Then it occurred to me that motors are kind of dumb in that if you give them bigger loads to move and supply them with the power, they will DO more work… until they melt. So the motors need to be upsized a bit, or at least have better cooling, which is really the same thing. But if this is happening as the outdoor conditions are getting really cold, that will help a lot to keep those motors cool as they work harder. One other thought I just had: In the case of air-to-water heat pumps making water in the 150 to 170 F range, that water could be used to cool motor heat sinks and put that waste motor heat to work.
Allison, I just received your book last week, Its fantastic but I haven’t had tome to dive deep into it yet.
I have a problem where I’m coming in on 21kBTUs on cooling at 27-29kBTUs on heating. I’m in Roanoke Va and in a 1972 house. Original windows still in it but I hope to upgrade at some point to double pane windows. I have installed a minisplit in the basement which used to be heated by baseboard electric strip and 1 7″ duct from the attic. MY 3 ton HP died last summer so I have been heating the house with the electric furnace. My issue is what Is it safe to go all the way down to a 2 ton HP VS such as the Daikin fit? (Mitsubishi parts and prices here are insane and most stopped carrying the products) My contractor recommends a 2.5 ton based on heating and according to him the FIT will modulate down and dehumidify also. I just want to save as much money as possible while being comfortable. My discrepancy between heating and cooling loads has me concerned. HDD here is ~3500 with design temps anywhere form 15-19*/CCD is ~1600 with design of 90 but it maybe closer to 91-92.
Im concerned because my old 3 ton ran almost all day from noon to 8pm most hot days and almost every day was hot. It kept up until you started cooking but it would quickly return to setpoint.
Is manual J missing my attic ductwork heat gain? Was my 3 ton with a 20*delta not supplying anywhere close to the 36000BTUs?
I just found your website via a post on Reddit and have been reading through some of the blog posts. I have a 70s era all electric house and my current heating system is resistive heating in my ceiling via a product called Ceil Heat. Needless to say it is NOT energy efficient by any means and costs a decent amount to run in Illinois. I’m hoping to upgrade to a heat pump at some point but I’m biding my time until the Inflation Reduction Act rebates start being available for the “HOMES Rebate Program” part of the IRA. I hope that your blog will have some focus on the “HOMES Rebate Program” part of IRA in addition to the more frequently discussed High Efficiency Electric Home Rebate Program (HEEHRP) part of IRA.
Assuming you do not have a ducted cooling system, I would go with a multi-unit ductless heat pump system but keep your electric heat in place for supplemental. This combination would give you fantastic zoning control for heating and cooling along with better than average dehumidification if you size the heat pump for your cooling needs.
Thanks for the reply. I actually do have a ducted cooling system but even though it still worked last summer it is past the end of its useful life. I definitely need to weigh my options between installing mini-splits for zone control or utilizing my existing duct work and not having any zone control. The combination of old cooling and expensive to run heating is precisely the reason why I’m looking into heat pumps. I wouldn’t mind throwing in a heat pump water heater too since my old WH is also quite elderly.
If your existing cooling system ductwork is in good condition, the least expensive option is to replace the cooling system with a heat pump system and utilize the electric heat in the ceilings for heating zone control and secondary heat to supplement the heat pump during very cold weather.
For the heat pump water heater, keep in mind that while it will help cool and dehumidify in the summer, it will also remove heat from the home in the winter to heat the water.
You can also install zone dampers in your ductwork and reuse it and have zoning.
Be careful just throwing zone dampers in existing ductwork. Ductwork should be designed for zoning due to the erratic increases in static pressure. By-pass ducts for ECM variable speed blower systems need to be mechanical, not pressure regulated. If putting zoning dampers in existing ductwork, be sure you can set the dampers to a maximum closing setting to allow some air to pass through the closed dampers when that zone is not calling for conditioning. Overall, I do not recommend zoning an existing duct system.
Robin, good advice. As a layperson, I wonder if there is much difference between dampening a zone’s trunkline or closing the registers for that same zone. I own a three-story rental rowhouse that I rehabed. I installed a two ton heatpump ducted system with a single zone but two remote senders for the basement and the top floor of the house. There are no trunk dampers. In the heating season, I close down the top floor registers to about 1/4 open. In the summer, it’s reversed closing down the basement registers. It’s still cooler in the basement in the winter but works OK in the summer. I’m assuming you would recommend against this practice.
For the application you are describing, it is best to put volume dampers in the trunk duct as close to where they take off of the main trunk or plenum. Once air enters a duct, it is very difficult to actually prevent that air from exiting registers or diffusers. All you wind up doing is raising the system static pressure while still letting air escape through the dampers or diffusers at a higher velocity.
I agree wholeheartedly with you Robin!!! I’ve seen many attempts of zoning a single ducted system and they make the system worse than before.
Great content as always Alison. Here in Maine we’re making homes heat pump ready because as you correctly note mean radiant temperature is critical to comfort. The most frequent comment we receive from clients who have made the switch to exclusively heating with heat pumps is that they are less comfortable than they were utilizing their previous Central heating system. We attribute this to two factors one they tend to keep the thermostat set at the previous set point as opposed to adjusting it to a comfort temperature. And the second is their first floor floors are considerably colder once they’ve stopped using their central heating system and the waste heat that they were contributing to their basement. We’re finding its critical to consider insulating the basement or crawlspace ceiling to increase its surface temperature as it typically drops significantly once switching from a basement located central heating system to heat pumps. We call this work making the house heat pump ready and heat pump comfortable. In addition, we’re making sure that we freeze proof the basement. Furthermore given that all shells are not created equally well we encourage homeowners to consider using / exercising their central heating system during the coldest of cold snaps to help overcome what may be unaddressed shell deficiencies and avoid frozen pipes and the nasty consequences that result from them. The message being that when it’s below zero that’s not the time to focus exclusively only on saving energy.