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Is a Heat Pump More Efficient Than a Furnace?

Is A Heat Pump More Efficient Than A Furnace?

The two primary ways you can heat your house are by burning a fuel (e.g., fossil gas, fuel oil, wood) or using electricity.  Furnaces and boilers distribute the heat from combustion to heat a house.  Electric resistance heat makes sense only in limited applications, so heat pumps are the best way to heat with electricity.  I love heat pumps and have replaced the furnace in my house with two of them.  But let’s get something straight here.  To say a heat pump is more efficient than a furnace or boiler is comparing apples to pumpkins.

Missing an important point

Unfortunately, a lot of articles on this topic miss an important point here.  Even some reputable sources make this mistake.  I just looked at three articles comparing heat pumps to furnaces and boilers and found these claims about heat pump energy use:

  • “more than twice as efficient as gas furnaces”
  • “a third less energy for the same output”
  • “much less energy than furnaces”

How can they make those claims?  Well, a good furnace turns about 95 percent of the energy in the fuel it burns into heat for the house.  A heat pump uses its input energy to move about 200 to 300 percent as much energy into the house in the form of heat.  Let’s put some numbers on this to illustrate.

You put 100,000 BTU of fossil gas energy into a furnace, and you get 95,000 BTU of heat delivered to the house.  You put 100,000 BTU of electricity into a heat pump, and you get 200,000 to 300,000 BTU of heat in the house.  If that’s all you look at, it would seem those statements above are correct.  You put the same 100,000 BTU of energy into the two types of heating systems.  Yet the heat pump puts 2 to 3 times as much heat into the house.  But something’s missing here.

What’s the catch?

The two types of equipment do different things.  A furnace uses the heat of combustion from burning a fuel.  A heat pump uses electricity to run mechanical equipment that moves heat from one place to another.  But we need to go further to find the real reason those quotes above are misleading.

Coal-fired power plant [by stanze, from flickr.com]
Coal-fired power plant [by stanze, from flickr.com]
When a furnace burns gas, it’s using a primary energy source.  When a heat pump uses electricity, it’s tapping a secondary energy source.  The electricity is just a carrier.  The primary energy in that electricity comes from:

  • Burning gas or coal
  • Harvesting the heat from a controlled nuclear reaction
  • Taming the kinetic energy of blades spinning in the wind or in a dammed river
  • Getting electrons to move when radiant energy from the sun hits a photovoltaic module

In the US, a lot of our electricity still comes from the first one in that list.  In the case of electricity generated by burning coal, the efficiency at the plant is 35 to 40 percent.  Factor in the losses as the electricity goes from the plant to your house, and you’re down to about 30 percent efficiency.  Gas-fired power plants are better but still only about 50 percent efficient, with the same transmission and distribution losses.

The bigger picture

When you use that electricity in a heat pump, you get about three times as much heat as electrical energy used.  That brings the net efficiency back up to the 90 to 100 percent range.  And that’s about the same as a high-efficiency furnace.  What happened to heat pumps being “more than twice as efficient “?

Now, the electricity that gets delivered to your house doesn’t come only from burning gas or coal.  The actual mix of primary energy sources depends on where you are.  In the Pacific Northwest, much of the electricity comes from clean hydroelectric plants.  Quebec has about the cleanest electricity in North America, with 95 percent being hydroelectric.  In Wyoming or Georgia, the electricity isn’t so clean.

Apples and pumpkins

Still, making a direct comparison to say a heat pump is more efficient than a furnace isn’t helpful.  To do so, you’re comparing primary energy used on site to secondary energy that comes from other energy conversion processes off site.

Don’t get me wrong.  I’m not saying you should avoid heat pumps just because the net efficiency might be no better than a gas furnace.  I’m just saying you can’t look only at the rated efficiency of the two types of equipment.  In addition, the rates that utilities charge for electricity and gas are different.

The good news, though, is electricity keeps getting cleaner as solar and wind grow like mad.  So, there are good reasons for going with heat pumps, including that they result in lower carbon emissions than a furnace in almost every state in the US.  (More on that topic soon.)  But choosing a heat pump because it’s more efficient than a furnace isn’t one of them.

 

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.

 

Related Articles

The #1 Reason to Have an All-Electric Home

The Electricity Multiplier Effect for Home Energy Efficiency

Heat Pumps, Auxiliary Heat, and Resilience

 

Photo of power plant by stanze from flickr.com, used under a Creative Commons license.

 

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This Post Has 78 Comments

  1. A great concise explanation. Ground source Geo exchange systems add another energy loss in the ground loop pumps howling away 24/7. However, as you stated – clean renewables like hydro, wind and solar are the game changer. Not only cleaner – but increasingly cheaper as long-term utility power purchase agreements slide down into 1.6 cents per kilowatt pricing vs about 8 cents for coal. Two good reasons we can expect renewables to rise to the top of the power generation pile. The pessimists are wrong – with current advances in battery storage, renewables are the future. The NEAR future. The elimination of fossil fuels from most grids is likely going to happen in the next two decades.

    1. Roy, I agree. We’ve already made great strides in cleaning the electricity from the grid, and that will continue. And that’s why it’s better to go with a heat pump, not because of an apples-to-pumpkins efficiency claim.

  2. Allison: What about gas-fired heat pumps? There are people working on this technology for residential applications using ammonia absorption technology. They are claiming Seasonal COP (SCOP) of 1.4 which would be equivalent to an AFUE of 140%. This would seem to be the most efficient in terms of source energy, at least until we get enough renewable electric energy that is available during those cold winter nights.

    1. Roy, I agree with that analysis. You’re actually comparing primary energy to primary energy, though, and my complaint in this article is people comparing the primary energy in gas used on-site to the secondary energy of electricity used on-site.

      1. I guess that I was just trying to point out that “gas heat” is not limited to 100% efficiency. Gas heat pumps do exist, but they are a lot more expensive and complicated than gas furnaces, even the high efficiency condensing ones. But all of this is moot if we eventually ban the use of fossil fuels.

        But there are people working on “green natural gas” and “green hydrogen”. Is that coming up in a future blog?

  3. In my world, when homeowners look at efficiency claims, they’re more interested in how much it costs to operate, not source energy efficiency. The problem is, few homeowners can extrapolate even the most accurate heat pump vs furnace efficiency metrics into dollars saved. (And don’t get me started on energy *savings* claims cited by the marketing gurus.)

    The math to make apples-to-apples operating cost comparisons with furnaces would be relatively straight forward if it weren’t for highly unpredictable supplemental heat energy in the case of heat pumps. Still, it’s possible to make thumbnail comparisons for a specific home based on local energy costs (and lots of observational experience).

    1. David, yeah, I mentioned the cost issue in the article, and you’re right. That’s what a lot of people care about, and comparing the operating cost of furnace to that of a heat pump isn’t straightforward.

  4. I have to agree with David. Most homeowners are only concerned about how much they are directly paying each month. The other costs are shared with all of the other homeowners no matter what system they use. The comparison that you are making also is for heat pumps that operate only in heat pump mode, which in Cincinnati is only part of the year.

    1. Matt, I agree. That doesn’t change the fact that when someone says a heat pump has three times the efficiency of a furnace that they’re using an inaccurate comparison.

  5. Such a great article I don’t even mind being one of the dunces!

    To take it a step further, what about “line losses” with fossil fuels – leaks along the way, in the natural gas distribution, etc?

    1. Dan, yes, that’s another important point. I don’t think it changes the efficiency argument, but it does bolster the case for heat pumps based on carbon emissions.

    2. Not only leaks, but there is a considerable amount of “natural gas” (methane) that is used to power the very large compressors that line the route from the source to the homes, or the electricity plant that is burning the gas. Many people seem to think that the oil and gas pipelines are magically filled and the fuel transported by unseen and non-energy-using forces. While such distribution losses in the electricity grid were noted in the article, the electricity distribution system is not the only distribution system that has significant losses!

  6. Good article but I struggle to see how this is different than the outdated “why buy an electric car if its powered by a coal plant” argument. Perplexing that you say all this, just to end it with “o ya but they do use much less emissions in almost every state but that doesnt mean theyre more efficient!” like…?? ok? Seems like they are considering the prior statement.

    Transitioning to renewables won’t happen over night. We must implement solutions to reduce fossil fuel consumption (in every aspect), while also increasing energy efficiency, storage and renewable generation capacity. Heat pumps + electric resistance is a great option in almost any context.

    Are we only allowed to tackle these issues once every coal plant is shutdown? What happens when the grid is primarily powered by renewables and we can more effectively store energy? Is that when we implement energy efficient techology? This transition must happen hand-in-hand and making horse before the cart arguments is only regressive.

    1. A, it’s not the same argument at all. I’m just saying that it’s not true for someone to claim a heat pump is much more efficient than a furnace by comparing a primary energy used on site to a secondary energy used on site. It’s not a valid comparison and making people feel lied to will not help get them on board. There are a lot of good reasons to go with heat pumps. Efficiency based on site energy is not one of them.

  7. I was just having a conversation last night with my friend. He currently has a VERY old oil furnace and straight AC with a coil slapped onto the top of the furnace. AC runs good though and for a frankinstein system the comfort isnt bad. The problem is him spending $500-1000 per year for oil. I told him straight up that a HP would save him money. The problem is when trying to calculate electric strip usage. Another problem I have is how do I calculate Air conditioning costs to Heating costs when using the same system when talking about the system minus the electric strips.

    1. Shae, yeah, he probably can save money by converting. The auxiliary heat issue is a wild card, though, as David Butler mentioned in his comment above. There are ways of minimizing that usage, but you’ve got to have someone who understands equipment to get the right design.

    2. @Shane, electric strips may not cost that much more than oil for heating. It’s easy to calculate:
      oil cost per therm = price per gal / 1.38 therms per gal / furnace efficiency
      electricity cost per therm = price per kWh x 29.3

      In both cases, blower energy adds roughly 10 cents per therm for standard PSC blower as your friend likely has, or about 5 cents per therm for a ECM or variable speed blower. But in the case of a heat pump, blower energy is already factored into the COP so we should add blower energy to oil cost per therm for apples-applies comparison of a heat pump + electric strips. If you were comparing to an electric furnace, then you must add blower energy.

      The supplemental fraction may be anywhere from 0 to maybe 40%. One thing folks fail to consider is that the colder the climate, the more heating hours you have above freezing when heat pumps typically need no supplemental heat. I can only narrow that down if I model a house and consider climate, and of course, the capacity of the heat pump vs the heat load. (The supplemental fraction can obviously be reduced by oversizing the heat pump, but this will reduce or eliminate latent capacity in cooling mode).

      In general, a tighter more efficient home will have a lower supplemental fraction, assuming the heat pump is properly sized for the cooling load. That’s because cooling loads don’t scale nearly as much as heating loads as you make a house more efficient (because of thermal mass and radiant energy, but that’s a whole other discussion).

      A heat pump’s COP depends on outdoor (and indoor) temperature, so the seasonal COP depends on climate zone and t’stat settings, but it’s reasonable to assume a COP of 3 for this type of thumbnail analysis. That means the heat pump will cost 1/3rd the amount you come up with for strip heat. The seasonal cost of a heat pump is simply the weighted average of the heat pump and electric strips, using the supplemental fraction as the weighting factor.

      When considering a specific model and size heat pump, it’s possible to refine the seasonal cost per therm with an accurate load model and combine that with weighted COP’s at each TMY temperature bin for the site (requires manufacturer expanded performance data). But it’s a folly to extrapolate the supplement fraction from that analysis. I have my own techniques for narrowing down the expected supplemental fraction once I model a home, but it’s always just a guess.

      The good news is that you can quickly come up with a couple of thumbnail estimates based on reasonable assumptions for the supplemental fraction, e.g., 15% and 30%, and in many cases, that’s enough to validate switching to a heat pump, especially if the only alternatives are fuel oil or propane. A lot depends on local energy prices, but I don’t ever recall a situation where it made sense NOT to switch from propane or fuel oil to a heat pump , and most cases, it didn’t make sense to keep the fossil fuel furnace as the “supplemental” heat source (except perhaps to use its blower instead of buying an air handler).

  8. Allison, thank you for this article. Heat pumps are excellent technology, but they are in danger of being over-sold. They are not magic. Given your skill at making complex topics easy to understand, I wonder if you would consider addressing comfort from cold climate air source heat pumps compared to furnaces and boilers. I don’t operate heat pump(s) myself, so I feel unsure about that subject. Often I hear about air source heat pumps not providing adequate comfort during the coldest weather here in New Hampshire, but don’t know if that is due to poor installation of the heat pump(s) or other factors. Certainly the COP declines at cold temperatures, but what about comfort? Thanks again.

  9. Great posts. In my town gas is very cheap and everyone told me to get gas for now and transition to electric when my equipment needs replacing in 15-20 years. However once you factor in the extra efficiency of the heat pump it comes out to almost the same cost. And I’m told that our NG prices are so low they aren’t sustainable.

    Fortunately the electricity in our state is ranked high in terms of source energy being clean. So I built a highly efficient house that doesn’t need much heat, and am using heat pumps because I don’t believe it’s all about cost. I believe we all need to transition as soon as possible, certainly every time we add or replace a new heating device.

    I also will be generating this power free eventually from solar. So looking just at the current cost of NG vs electricity is short sighted.

  10. Allison, I agree with your analysis from a physics of primary/secondary energy angle (with a bunch of smallish caveats such as gas pipeline operation, distance from power plant, seasonal efficiency fluctuation of power distribution, etc), but if we are after emissions…
    While we are in the process of gradually dropping the fossil fuel habit, the argument against a vast network of distributed, hard-to-control burn sites, aka gas furnaces vs. one burn site, aka the power plant, has to continue. Unfortunately.

      1. I really look forward to that one! It is interesting how there are two major factors that have come up over and over again in this particular discussion. The majority of folks point out (correctly) that it is all about cost for most consumers – then there are those of us who are most concerned with reducing GHG emissions – BUT – they are two sides of the same coin. The world is starting to feel the bite of climate change, and the costs are going to be breathtaking. If consumers had been, or were now, required to pay up-front for the future costs of mitigation, the factors shift dramatically. Unfortunately we really don’t have accurate models to calculate the future cost and assign them to GHG producers, and it is doubtful that we will be able to do so (or find a fair way to apply them even if we do develop them). Maybe cutting out subsidies and tax breaks to fossil fuel producers would be the first step?

  11. ;My’ Mitsubishi installer, installs the outside, part – of the heat pump – as in the picture – close to the wall. I wished that this was installed at least a foot away from the wall and with a deflector, for snow from a steel roof – or install it on a gable end.

  12. As usual, gratitude for a great article & education, Allison! & I always learn lots from commenters–thanks to you all also! Re ‘apples-to-apples’ comparison, I agree with several other commenters: if 1 is considering ‘energy/efficiency losses’ for electricity on the way to the house for electric heat pumps, then shouldn’t we also consider equivalent transmission losses for gas to arrive at a house [power to achieve pipeline pressurization; pump stations along the pipeline; periodic ‘releases’ of gas due to pipe leaks & pressure equalization releases of gas, etc]? Or am I brain-fogged about that? As a mid-Atlantic 30 yr heat pump user, I agree with commenters re the ’emergency’ electric heater elements factor. Historically we haven’t had to use that heater element very often. But as climate change has brought great variability & fluctuation to our local weather, during cold weather last yr & now already this yr, there are an increased # of nights when the electric heater elements kick in to maintain our heat setting at 69 or 70 in our 1960s still somewhat ‘leaky’ house.

  13. Building in the Raleigh NC area I have many of customers that refuse to use a heat pump for 2 reasons; 1. Once outside temps hit freezing heat pumps struggle to maintain warmth, 2. Most of our northern transplants have not heard of them or do not know of anyone who uses one up north, so obviously they can’t be good. I know technology will continue to improve, as will all home heat sources will improve. As for the statements above are an aggregate of opinions and discussions I’ve had will locals and transplants alike.

    1. From everything I hear they only struggle if you have a pretty leaky house, which admittedly there are a lot of. But some of that feeling might be based on old technology. People are using them effectively even up here in CZ 6 (cold). Even though the COP is lower when you approach 0 and below, we don’t spend much time below 10. Most of the time where I am it is 15-35 in winter, and 6+ months a year is shoulder season where it’s in the 50’s, either all day or just at night. At those temps the COP’s are pretty good.

    2. Marc, as Cindi said, heat pumps can perform poorly in houses with bad building enclosures. But that’s not the only reason. They also perform poorly when the wrong type of system is installed, or if it’s the wrong the size. Very good cold climate heat pumps exist now that can heat homes very well. I like to say that a BTU is a BTU, no matter if it comes from a furnace, a heat pump, or a blow dryer. To keep the house warm enough in winter, you just have to supply enough of those BTUs.

      Here’s an article you can refer doubters to:

      Can a Heat Pump Work in Minnesota?
      https://www.energyvanguard.com/blog/can-a-heat-pump-work-in-minnesota/

      Gary Nelson heats his house in Minneapolis with a heat pump…and no auxiliary heat!

  14. I relocated from SW Colorado to Northern Arizona last year and cooling is more of an issue. I am considering adding mini splits for heating and cooling and moving away from evaporative cooling and transitioning from electrical central air and gas furnace. How does air conditioning factor in with this option? I have been told cost compares with ‘swamp coolers’ / evaporated air. I am in the Verde Valley on the river so it is more humid than the close by desert.
    Great discussions as always, have been following for awhile, thanks everyone!!!
    Tim

    1. @Tim, swamp coolers are thought to cost less than AC during the dry months when they work well, but as I’m sure you know, they don’t work well during the Jul-Aug monsoon season, so any operating cost comparison won’t be apples-to-apples. OTOH, it sound like you already have central AC? If so, mini-splits will likely cost less to operate (unless existing AC is variable speed). As for heating, if the existing furnace is propane, mini-splits will save at least 50% on heating costs (a LOT more, given current propane prices).

    2. Tim, air conditioning uses significantly more energy than evaporative cooling but has some significant advantages. As David Butler mentioned, swamp coolers aren’t a year-round solution for cooling. In addition, they require a lot of maintenance. And if you’re ducting the cool, humid air, it can grow mold in the ducts and rust them out. Here’s a photo a contractor friend of mine in Arizona sent showing what can happen:

      Duct rusted out from humid air from swamp cooler

      1. Allison and others,
        I appreciate all the recommendations and conversations!
        A bit more info:
        There is an aging central air unit not worth putting more dollars into but it gets by. That and the natural gas furnace could be replaced by a ducted heat pump system.
        The existing ductwork was not optimized when a porch was enclosed and ceiling vaulted so it is under heated or cooled depending on season. That is where a dual head mini split would be added.
        Allison, I have been following your website and this blog since we met at a session during the Passive House conference in Denver some years back. I believe may have had some beers later.
        I have designed high performance homes ( LEED Platinum, Net Zero, non certified PassiveHaus and others) for many years and rely on these and other similar conversations to increase consciousness of these issues for myself, clients, contracters and building officials. Keep up the awesome work everyone, increasing the knowledge of importance of well designed and installed HVAC systems and importance for the dwelling we all occupy. Thank you all!

  15. One more consideration for the ‘overall cost’ argument: while gas might be cheap, the providers are adding increasingly higher fixed monthly costs (esp. in Texas to ‘recover’ from the 2021 storm), resulting in ridiculous bills where the monthly bill will not be less than $30 regardless of gas usage. Electricity providers have done similar things but not to the same outrageous (imo) extent.

    1. Otoh I couldn’t help but notice people in Texas trying to heat their homes with gas stoves

  16. Does this factor in the emmissions from generating the primary source – aka, producing and transporting that coal/gas/oil? Seems a bit unfair if not, especially given the losses accounted for on the electricity grid in the article. Presumably piped residential gas is lossy and oil delivery is usually a giant diesel truck…

    1. Dan, I’m just dispelling a misconception in this article. Yes, the emissions are absolutely important to seeing the bigger picture. Here’s what I wrote at the end of the article:

      “The good news, though, is electricity keeps getting cleaner as solar and wind grow like mad. So, there are good reasons for going with heat pumps, including that they result in lower carbon emissions than a furnace in almost every state in the US. (More on that topic soon.)”

      I’ll cover the emissions side, which includes leaks from gas pipelines, in a separate article.

  17. Another thing that few think about is that with a heat pump that noisy annoying thing outside. Yes the compressor and it’s fan run when you want heat. Here in Crematoria(Texas) we have to listen to those things run for hours and hours and hours all 9 months of summer. The last thing we want is for it to keep running in the winter time and Oh yeah it makes way more noise in the winter when it goes into defrost etc.

    I know of many people that will go back to resistance heat when their system needs replacement. My parents in fact did that a few months ago. That little bit of time in the winter without having to listen to a compressor are well worth the slightly higher cost of operation. Seems no one is thinking about the livability of heat pumps. And also since our AC units run so many hours here the last thing we want is for that compressor to be running more hours in the winter shortening it’s life that much more when there are other heat choices.
    There is more to the equation than cost of operation. There is the human impact of the system, reliability, ease and price of repair and cost of the system when new and for replacement time.

    Then there is also the 20-25% power transmission losses that isn’t part of anyone’s equations to weather heat pumps are truly more efficient. Now if you have your own solar panels or another situation then it’s a no brainer.

    1. When I moved to SE Arizona in 2006, I lived in a cookie cutter neighborhood with 1/4 acre lots and couldn’t hear my neighbors’ air conditioners from inside the house (perhaps because our windows were double pane… are yours?). The exception: when we opened the bedroom window at night in spring and fall, our immediate neighbor’s AC was audible. But I certainly wouldn’t have considered admonishing him for running his AC when it’s cool at night.

      I realize your comment wasn’t about air conditioners but isn’t it the same thing when you argue that people shouldn’t buy heat pumps because you don’t like the noise?!

      As for the other considerations you mentioned… A heat pump actually costs significantly less up front than the equivalent A/C + furnace. Repair costs could go either way. A friend recently paid more than the wholesale cost of the furnace to replace his recently-out-of-warranty heat exchanger. As for A/C vs heat pump longevity: compressors are much more affected by cycle count than run time and in any case, anecdotal evidence suggests heat pump failures are more likely to occur when outdoor unit is stressed by summer heat than in winter. Today’s variable speed compressors have much longer runs times and thus far fewer on/off cycles than Paul’s uncle’s heat pump (or your air conditioner). Moreover, variable speed compressors and fans have virtually no inrush current, the primary stressor of motors, and as Paul demonstrated, the compressors and fans are much quieter.

      Bottom line, your argument against heat pumps (btw, this is the first time I’ve heard this) holds no water in the general case. You might get more traction if you were advocating for for ground source heat pumps, which have no outdoor unit. In any case, you’re free to spend 3x for straight electric heat.

      1. For the non-variable-speed heat pumps (and air conditioners), the inrush current (and thus a significant part of the noise) can be successfully controlled by using a “soft start” device. These are the opposite of a “hard start” device or kit that some installers may recommend and/or install, because they greatly reduce that initial inrush current rather than adding more inrush current from the additional capacitor in the hard start kit. The soft starters also reduce the impact on the compressor motor and thus improve the longevity of the system, while removing these multi-kilowatt spikes from the grid demand and the noise from the environment.

  18. I read an article in bloomberg I found helpful. It explains that converting gas (and especially oil) to electricity or kitchen power is far less efficient than converting then to heat. In fact, most of the process is waste heat (two thirds for gas, 80 percent for oil). This is fundamentally why it makes sense to convert motive power to electricity (the grid is better than 20 percent efficient) but also why focus on home gas usage is misplaced (versus insulation). Moreover, do heat pumps not vary in efficiency? It is this variability that is often the basis for hybrid systems (which essentially let you play the market for home heating). The colderit gets the more energy they need for the obvious reason that there is less heat to be moved indoors? Fwiw we have both a gas boiler and a heat pump, the latter of which we primarily use for air conditioning and shoulder season heating.

  19. I’m an HVAC contractor that installs HP’s, gas, propane, oil and geothermal so I’m agnostic about the appliance. They all have a place and all have weaknesses and strengths. This push towards “electrification” is going to become interesting for those of you in very cold or very hot climates. I hear talk about 100% renewables (solar/wind) in 10 years, 20 years and batteries are wonderful, ect. What happens when the sun doesn’t shine for days on end and the wind doesn’t blow like is happening in northern Europe now? Why is Great Britain buying nuclear generated power from France now? What happens when batteries are cold? Do wind turbines spin when there are storms? How much earth is disturbed when you start scaling battery production? What do you do with old lithium batteries? Where is the plan to dramatically increase the strength of the electrical grid as we rush to close nuclear and coal power plants? What is power grid inertia and can renewables provide it? Who/when/where is/are building the monumental amount of transmission lines that renewables at scale will require? Where is THE PLAN for all this? We build homes with plans, where is THE PLAN to “electrify” the US and maintain our current lifestyles? Can you operate your HP and strip heat on a gasoline generator? You better find out before the brown/blackouts occur. Meanwhile I will be sitting in my 1st stage HP heated home with oil/propane 2nd stage and backup generator, nice and cozy. Nothing as secure as fuel on site. There is an solution to electrification that is scalable and safe and
    can handle all our needs and its called nuclear. But I’m just an HVAC guy.

    1. Nuclear is “safe,” you say. One of the actual problems is one that lasts for thousands of years: disposal. Disposal of the “spent” fuel rods (which actually still have a lot of radioactivity in them), of the reactor itself, and even the enclosures that are necessary to contain the radioactivity in order to keep it out of the general environment and the people who work at the plant. All of these structures become radioactive because of the nuclear reactions that are the source of the energy produced by the plant. Such plants are almost always built a long distance away from population centers, for safety reasons, and thus has increased transmission losses (and costs). And don’t forget the huge amount of water that is needed for cooling, and the (negative) impact of said heated water on the environment into which that heated water is discharged.

      Getting back to disposal, consider the fact that the US has never implemented any plan to manage the radioactive waste. A repository was designated in 1987 and infrastructure was built (Yucca Mountain) but it remains unused. For decades. So the radioactive waste resides at every plant site, since it cannot be transported to the repository.

      Also look at the actual costs, not the costs claimed by utilities which want to build a nuclear plant, such as Southern Power, the parent of Georgia Power. Their latest two nuclear plants (Vogtle) are many years behind schedule (supposed to be operational in 2016, and now, maybe, in 2022 or 2023, after failing to be done at the previous “definite” times, which roughly move one year every year, along with the rising costs), and real costs have ended up about double the “absolutely certain” costs originally claimed when they got the public utilities commission to allow them to charge customers for the construction costs long before even a single watt would be produced (which has turned out to be even longer!). The roughly $25 Billion cost will be doubled again when the true, full decommissioning costs are added, and the decommissioning will probably take as long as it took to build. And then, what to do with all of that radioactive construction material?

      I’d hardly call any of that scenario a description of a “safe” energy source.

  20. I have real trouble with statements like: “The good news, though, is electricity keeps getting cleaner as solar and wind grow like mad.” You are just trading one problem for another. The visual, sight, landscape, and physical pollution from all the “madness” (madness -as a psychological term) of wind and solar, is something we will be cleaning up 50 to 100 years from now. There are better, cleaner options, and the sooner we can get them mainstreamed the sooner the madness stops.
    I think other than that you are spot on with this article.

    1. I guess the mercury being pumped into the air by coal plants is okay then because it’s out of your sight and impacting someone besides you.
      I personally find solar panels and wind farms beautiful.

  21. Sue, you might want to go back and read my original post, it said nothing about supporting coal.
    I was comparing the pollution of solar and wind to the offensiveness of coal. One pollutes the air, and the other pollutes the land, kills the avifauna, and destroys the visual landscapes. Trading something Bad for something Terrible isn’t progress, it is just kicking the can down the road. Especially when there are far cleaner, safer, less obscenely obtrusive options.
    As a side note- people use to think the coal smokestacks were beautiful (and a sign of progress). Not my cup of tea.

    1. Tad Englund, of course there is always something better, but we are all anxiously anticipating your telling us what those alternatives are that you favor, and why.

      1. Look at Finland and also read the post just above mine, again. Paul, one could write many books explaining why.

  22. Great blog post. I was just talking to a friend this week who wants to ban natural gas. I pointed out how my city of Bellingham, WA has been moving towards banning natural gas but we have a natural gas plant here in our city.

    Also according to Puget Sound Energy’s website while they have a very clean fuel mix Coal is actually the biggest energy source in the fuel mix. So we ban natural gas appliances and yet plug in to a grid that is coal/ng powered. Makes no sense to me.

    Anyways I digress. Allison would you care to write one day on heat pumps for heating in colder areas. Im an hvac installer and mostly do new construction custom homes and gas furnace change outs and today was the first day I did a change out on a furnace with a heat pump. When I got it going I was shocked at how not warm the “heat” was. My boss said it was because it was 44 degrees out and heat pumps just dont perform well in our cooler climate. I will admit I am very ignorant on this topic.

    Also want to say how much I appreciate your website. It has made me a much better HVAC installer and I will never look at flex the same way.

    1. Kurt, skipping to the heat pump discussion, let me say first that a BTU is a BTU. It doesn’t matter whether it comes from a furnace, a heat pump, or the heating element in the oven. If you size a heat pump correctly and account for its changes in performance as the outdoor temperature changes, there’s no problem with using a heat pump in a cold climate. (Bellingham, of course, isn’t a cold climate, but you know what I mean.) Your boss seems not to understand heat pumps either because they actually can perform very well where you are. And 44 degree air has a lot of heat in it!

      I’ll write more about heat pumps soon, but here’s an article you can read about a heat pump in Minneapolis:

      Can a Heat Pump Work in Minnesota?

      1. Ah! Perfect explanation. I wonder if maybe the old heat pump was undersized or not performing well for some other reason. We did not install the old heat pump just changed the furnace out. Thanks again for all the info on here!

        1. What you are seeing Kurt is the difference in heat rise for two types of appliances rather than a difference in BTUS. Basically the difference between heat transfer surface area vs. surface temperature vs. airflow volume / velocity. It is a natural reaction when people feel the higher temperature of supply air from a gas or oil furnace for them to assume there is more heat – and there could be if the previous appliance was over-sized (which they almost always are). Slower recovery from night setback often has people blaming the new right-sized heat pump.

        2. @Kurt, as noted by Allison and Ray, heat pump supply air isn’t as warm as a furnace, but that’s a good thing in modern construction — the more efficient the house, the lower the supply air needs to be. For example, the supply air in my own home drops into the mid-80’s when it’s in the 20’s outside, but a 15F delta is more than enough to maintain the house at 70F. Supplemental heat doesn’t kick in until it drops into the teens.

          The 130F to 140F supply air typical in a furnace actually CREATES comfort issues in a tight, well insulated home (just as a radiant slab can create comfort issues in a modern home if the supply water is warm enough to deliver the ‘warm toes’ promise). In 21st century homes, if supply air “feels” nice and warm by 20th century standards, then the heating appliance is too large and will short cycle. The large contrast between hot supply air and “room temperature” air off-cycle, combined with short cycling, is what causes comfort issues. By the same token, older, leaky homes are poor candidates for heat pumps as primary heat source, but it’s a relatively inexpensive upgrade when the A/C needs replacement (i.e., dual-fuel heat).

          You can raise the supply air temp by reducing the blower speed (my system does this automatically), but the key to avoiding comfort complaints with heat pumps is strategic placement of supply diffusers (or use directional grilles) to ensure supply air doesn’t blow directly on seating or standing areas, or beds. Also, consumer education is vital. You don’t want to install a heat pump in a home if the owner is dead set against it. But I find most people open to learning more about heat pumps. Unfortunately, people like your boss are hampering adoption.

          I still occasionally specify furnaces in new construction in cold-climate states with high electric rates when the site has access to inexpensive natural gas. But as every mechanical designer knows, in order to get sufficient cooling airflow, you end up with a furnace that’s way too large for the load. As I noted in an earlier comment, heat loads scale much faster than cooling loads as we beef up R-values and tighten the enclosure, and furnace manufacturers haven’t adjusted their products accordingly.

    2. “So we ban natural gas appliances and yet plug in to a grid that is coal/ng powered. Makes no sense to me”
      Putting the cart before the horse

    3. “So we ban natural gas appliances and yet plug in to a grid that is coal/ng powered. Makes no sense to me.”
      You are right, except… I’m sure they want to ban “new” NG appliances, but the existing ones will still be around for 20 years. Requiring new equipment be electric is a good way to slowly phase out NG and phase in electric in a way that isn’t super disruptive. It also sets homes up to easily cover their heating loads with rooftop solar.
      Also electricity has been improving faster than many realize. I was told by all the ME’s and builders in town that our electricity wasn’t “clean”, but in fact we rank #2 or 3 in the nation for clean power generation. Which isn’t to say it doesn’t have a long way to go. But many people just aren’t aware how generation is moving to cleaner sources since it’s actually cheaper to generate power from solar and wind farms now than fossil fuels. They’re saying their new solar farm they can generate at 2.2c/kwh.

      1. I think the opposite is true, people underestimate how difficult the transition will be. Solar and wind are unreliable so they require backup generation. Most countries that are ahead of us pay significantly more for power. Grids require reliable power to work. Texas could improve its gas and nuclear powers ability to operate in extreme cold but they couldn’t force the wind to blow or the sun to shine. If people electrify their transportation, which offers more benefit than home heating electrification, we will need to generate more electricity over all. As for gas bans, what happens to the gas grid when only older homes and fewer of them have gas? Who pays to keep it up? Who Is going to invest in something that is banned? It’s going to happen faster than you think and cost more than you think, imo. Meanwhile technologies are changing from everything to paint to insulation that will help reduce consumption. Personally I have both a heat pump and a boiler, both are better than forced air imo. Over time I hope to convert the boiler to a hybrid but for the time being the heat pump on the third floor is enough to cool the whole house on all but the hottest days.

        1. Here’s the thing.

          We await your responses – these are all good questions – don’t expect others to answer them for you.

          The best approach to getting answers to the questions you have just asked – is to do the research and answer them yourself.

          Let us know what you have found out 😎

      2. I agree that banning new NG hook-ups, while purported to be long sighted, is actually short sighted for exact the reason city by Andre — remaining gas customers in those communities will be charged higher and higher distribution charges as the customer base shrinks. A political time bomb.

        OTOH, I’m far less concerned about electric grid reliability as generation shifts more toward solar and wind. Those changes are happening on the supply side (i.e., no one is banning new electrical hookups), so those who manage and finance supply side solutions will sort it out based on marketplace forces.

        As coal generation subsides (mostly due to marketplace forces than political interference), fast spin-up natural gas generation plants provide grid stability and will continue to do so for the foreseeable future. No one is proposing a ban on gas peaker plants. Battery technology and economics will eventually catch up and complete with gas. OTOH, I believe nuclear base load generation will (eventually) stage a comeback, relegating coal to the history books.

        Natural gas, while a fossil fuel, is among the least impactful in terms CO2. But it needs a LOT more regulation in terms of methane release. That where attention needs to be focused, not on banning new gas hookups!

        1. The problem with banning gas usage is that it’s actually a lot more efficient to generate heat at home than to import electricity into your house, rule of thumb is by a factor of three. The main advantage of natural gas is the natural part, it’s unrefinedaking its overall impact lower. The distribution network could be tightened up (and as far as I know that’s already happening and has been for several years, fortunately by volume leaks are fairly concentrated) but in the end, gas loses two thirds to heat when it’s converted to electricity, then there’s line losses. Gas at home otoh can be up to 97 percent efficient. I recognize climate plays a big role and also recognize that a passive house is fairly different from an old home which itself will drive changes without an outright ban.

          Btw, I also agree nuclear will play a larger role. It is more reliable than renewables (generating the same amount of electricity year round) and can generate huge amounts of power. If we’re lucky, there will be a fusion breakthrough and all this talk will seem quaint.

          1. Andre, I think you missed an important point. Heating with a gas furnace and with a heat pump uses roughly the same amount of energy. Yes, gas is three times as efficient as heating with electric resistance heat, but that’s not true for heat pumps. A coefficient of performance of 3 makes them roughly equal.

          2. Ah yes – nuclear – the source of the most toxic materials mankind has ever produced. No one has ever figured out how to neutralize and / or process the volumes of nuclear waste being pumped out by the current generating stations and so we will need to protect and guard this stuff in safe locations for over 100,000 years (no human government has ever lasted 1,000 years).
            The original post and it’s simple point have wandered far and wide – but that is great – this stuff does need to be talked about.

        2. I think the goal of the ban is really to stop people from choosing to cook with gas because once they have a gas hookup then they have choices and choices isn’t the goal.

  23. Alison I did see that and where you qualified that this applies to where Temps are generally above 40 degrees since heat pumps do get less efficient as Temps drop (which is problematic in a cold snap). I still don’t support an outright ban, cooking with gas isn’t the problem. I’m also a huge proponent of redundancy. I watched a show on German heating and this one household had three types of heat, two of which were subsidized by various energy efficiency programs. They kept the old ones so they had a choice of wood pellets, gas, and I think oil (not positive what the third one was). The household then chose whatever heating made the most sense based on market prices. A dual fuel household would have that same advantage.

    (Of course, only nuclear France ever achieved any modicum of energy independence, Germany is still quite dependent on Russian gas)

    1. Andre, yes, Germany is an energy hog and a strange case (just opened a 1GW coal-fired plant, apparently replacing its remaining older sister plants),
      https://www.eia.gov/international/analysis/country/DEU
      yet their current 40% of power generation from renewables vs. our 14% (https://www.eia.gov/outlooks/steo/report/electricity.php) is something to aspire to, not to mention their goal of 65% by 2030. Strange, because Germany also plans to put all coal-fired generation offline by 2038.

      And that example you cited about a household with 3 CO2 generating sources of heat in one household maybe is an early warning on how Germany will cheat in 2030: yeah, we generate 65% of our electrical energy from renewables, but don’t ask us how we heat our homes! (OK, I am just having some fun on a balmy Sunday morning in GA in November, at 53F.)

      1. Paul, Germany is way ahead in some ways. They pay far more for power and renewables have been driving up the cost of power, especially once you start to get to more than a third of generating capacity. Getting rid of coal and nuclear has made them more reliant on Russian gas (not something to aspire to). The world contains lessons if we are willing to listen.
        David- are you saying heat pumps are not less efficient in cold weather?

        As for nukes, I dont see the us being dependent on winds blowing if there is a breakthrough in fusion. You might as well start making out your checks to Xi. Nuclear has already seen many advances technically even if people’s views of it haven’t changed much since 1978. Imo.

        1. They are less efficient in cold weather, but still pretty good until you get well below 0. https://ashp.neep.org/#!/product/51517 This site publishes COP’s at various temps. This is the Daikin unit I’m getting and you can see the COP at 5F is still 2.15-2.44, but it goes up to 3.73-4.5 at 47F.

      2. @Andre wrote:
        > are you saying heat pumps are not less efficient in cold weather?

        Not at all. The 3 (COP) that’s been mentioned in this discussion is a reasonable estimate of average or seasonal efficiency. The COP does indeed drop with temperature, as I clearly noted in my comment.

        Note that these numbers don’t include strip heat, which by definition has an efficiency of 1.0. In case you (or others) are interested, here’s some heat pump math:

        If we determine that the supplemental fraction in a given home is 15% and the heat pump’s seasonal efficiency is, say, 3.2, then the seasonal efficiency of the combined system would be the weighted average, or about 2.9 COP ( 0.15 x 1.0 + .85 x 3.2). You can refine this for a particular climate by weighting the COP at each temperature “BIN” by the number of hours (extracted from a location’s TMY data). However, the supplemental fraction can only be determined through monitoring. In my experience, homes built to today’s energy codes that are well sealed, located in a moderate climate (CZ3 & CZ4) will typically have a supplemental fraction of less that 10%, assuming the heat pump is sized to not exceed the cooling load by more than 25%. In dry climates where latent capacity in cooling mode is not a concern, you can further reduce the supplemental fraction by adding another half ton.

    2. @Andre, I’m not sure what comment of Allison’s you’re referring to, but 3 COP is a reasonable proxy for a heat pump’s SEASONAL efficiency. A mid-efficiency 2-ton heat pump (single stage with ECM blower) typically has a SEER (cooling) rating of 16 and an average (seasonal) COP greater than 3, depending on climate. Here’s an example:

      Amana ASZ160241L heat pump + ASPT29B14A air handler
      47F – 4.0 COP
      30F – 3.0 COP
      5F – 2.0 COP
      ref: page 18 in ASZ16 technical guide

  24. In agreement with David that today any politician proposing killing NG appliances might as well retire that same day. We also know that buildings are just one part of the reductions in CO2 emissions we all (hopefully) seek. Besides buildings, there is transportation, and agriculture (methane), and every sector and every individual that directly or indirectly contributes by causing the reliance on how the other sectors behave. Methane emissions from gas and oil wells, for example, would be reduced with reduced demand for those fuels.

    On NG CO2 emissions, I disagree that we can label it not significant and focus on just methane. https://www.eia.gov/tools/faqs/faq.php?id=73&t=11
    says that NG releases roughly half of CO2 when burned compared to the worst type of coal (anthracite), and 71% of diesel.

    On comfort and furnaces (high supply air temp), this dance has been performed for decades, if not centuries in buildings. Thermal comfort of a person sitting on a chair in the middle of the room in heating season largely depends on the radiant factor, unless the drafts perceived by the sitting person are “true” drafts (in which case the house is beyond leaky).

    A “solution” to those convective drafts has been the “nice and cozy” high supply air temp generated by furnaces. Don’t have a reliable source for this, but my guess is that majority of builders and HVAC installers are still participating in this dance, i.e. build the house as well as possible/cheap/fast/fill-in-your-goal and fix its shortcomings with supply air/water temperature.

  25. As I mentioned in my previous post, I like HP’s as primary heat in my cold (MA&NH) homes, but they are backed up with oil and propane respectively if the need arises. One thing not mentioned is commissioning of said HP’s. As a 35 year HVAC guy, I will be the first to say that the skill level of the average HVAC tech is shockingly poor and probably not going to get a lot better unless more people enter the trades and quality training backs them up. Electrification is about to hit MA this winter and the utility push to offer huge rebates (up to $10K!) to replace fuel appliances and install HP’s has insulation contractors rushing to jump on the HP gravy train. More novice HP installers… what could go wrong? The weakness of relying upon a HP with 0 back up heat (electric strip, gas, oil) is the high possibility that the HP is not going to reach the rated capacities and efficiency because it is not charged or installed properly. Maintenance, refrigerant leaks, and the fact that any major repair needed in severe weather is very difficult to perform since 1/2 of the system is located outdoors and EXTREMALLY complicated (tech will likely need to call factory tech support). Will a HP heat well below 0 degrees…you bet it will in the lab, but the real world is a very different place. BTW, wind/solar is much more expensive per kwh WITHOUT subsidies, your electric rates will continue to climb and the poor will take the hit as usual. Lastly, research how much child/slave labor goes into sourcing raw materials for solar panel and battery manufacture, Tesla’s will look less cool I bet. The world is much more complicated, so let’s not destroy the earth (and our standard of living) in a haphazard quest to save it.

    1. Rich, regarding electric rates and renewables, these yesteryear “opinions” need some updating. Today, the levelized cost of energy ( look it up) is lowest for solar, followed by wind, followed by NG, geothermal, and coal, in that order. The most expensive is peaker gas.

      Regarding forced labor in PV production, main culprit was responsible for 1.8% in recent solar imports (2 1/2 years worth of: https://www.nytimes.com/2021/06/24/business/economy/china-forced-labor-solar.html) and is being dealt with (https://www.cbp.gov/trade/programs-administration/forced-labor/hoshine-silicon-industry-co-ltd-withhold-release-order-frequently-asked-questions). Will there be more bad apples? Sure.

  26. I’m all for electrification. I do think we have some massive investments to make in the actual grid. Both the age and capacity are going to be very expensive and complicated problems. Especially as we shift both transportation and climate control to full electric.

    I like clean energy, but there’s no such animal at this time. All have some environmental costs.

    Solar panels have sort of an expiration date and they can be destroyed by hail and other natural events. There’s a ton of them that will be heading for landfills. Not to mention the manufacturing and mining of raw materials.

    Wind requires LOTS of regular mechanical maintenance including parts replacement and petroleum grease. They pose a large direct environmental impact due to their footprint and they kill migratory birds.

    Real fusion power is a pipedream in its’ current state. Once the experimental phase is seen through AND if it really works, only then can we set a real timeline. If I had to guess, at minimum it’s probably another 50+ years out before it even has a chance to be part of the electric generation mix.

    Fission, however, is not dead yet, and it shouldn’t be. The newest generation of reactors (Gen IV) in development can even run on the old fuel that is sitting in bunkers. The efficiency and safety are incredibly high compared to “your uncle’s” Gen II style reactors. It’s only a matter of time before the field develops designs that are considered inherently safe, where even operator “accidents” are not dangerous to people or the environment.

    MIT has had a reactor operated by students for more than 60 years without incident. If you’ve sworn off nuclear as too dangerous or hazardous it might be time to give it another look.

    1. I just wanted to add that nuclear has been kind of stuck in this cycle of rebuilding and maintaining old reactors because the NRC has a moratorium on new reactor construction. The public’s distrust, given the disasters we’ve seen, is warranted. However, this cycle of patching old tech has to end at some point. Especially given the promise of more efficient and inherently safer designs are getting very close to being a reality. This combined with the ability to recycle old fuel means, to me, it has to be on the table.

      We have a long road to get to fully electric. A lot of different energy sources will get us there. No matter what technologies we choose, one thing is certain, our aging grid needs a LOT of improvement. We’ve seen too many failures due to lack of maintenance and capacity. That trend will only get worse as demand rises and we push it harder.

      1. “The NRC has a moratorium on new reactor construction.” A false statement. There are two nuclear plants currently under construction in Georgia (Vogtle), for $25+ Billion. The Watts Bar nuclear plant began delivering electricity in 2016. And a new nuclear plant has recently been proposed for construction, with backing from billionaires, who seem to be anticipating building it at a cost that is a mere fraction of the cost for the Vogtle plants, but that will likely balloon in the same way that every other nuclear power plant cost has ballooned.

  27. Very well worded explanation for comparing heat pumps to gas furnaces. Your words will make a great addition to what I usually say when asked; “Which is better, a heat pump or a gas furnace?” My usual snarky response is; “Yes.”
    Actually, when gas is already available, I usually recommend a mix of heat pump and gas furnace technologies. I’m a big fan of being able to choose an energy source for heating.

  28. Does anyone know of a good software or spreadsheet that can compare the operation costs of a furnace and AC system to a variable speed heat pump system either ductless or ducted?

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