Evolution of Heat Pump Technology

We can expect material improvement of heat pump efficiency over the next few years. Improvements likely to reach the market within two years will involve a shift in refrigerants that will improve conventional air-to-air heat pump efficiency by 10% or more, while reducing the climate risks of refrigerant leaks. From an environmental perspective, it may make sense for some homeowners, especially those who heat with gas and who do not have an immediate need to replace their heating system, to wait for the next generation of heat pumps. During that pause, consumers could focus on improving the insulation and general energy efficiency of their homes. Longer term improvements are harder to project, but we can hope for air source heat pumps capable of heating water hot enough to use in existing home radiators.

Evolving regulation of refrigerants

Heat pumps cycle a refrigerant fluid through compression and expansion to move heat from a cooler place to a warmer place. The characteristics of an ideal refrigerant fluid include:

  • Stability
  • Thermodynamic properties that favor efficient heat pump operation
  • Non-toxicity
  • Non-flammability
  • Not too harmful to the ozone layer
  • Not too harmful as a greenhouse gas

Heat pumps have been around for a century in various applications — air conditioners, chillers, refrigerators, ice machines. The set of chemicals available to use as refrigerants has been well studied. The last few decades of changes in refrigerants has reflected evolving public policy more than chemical innovation.

Since the world banned ozone-depleting refrigerants, the refrigerant used most commonly in heat pumps in the United States has been a chemical mix known as R-410A. See this note for an explanation of the numbering system used to identify refrigerant chemicals in the hydrofluorocarbon or “HFC” family.

R-410A, like other HFCs is a very potent greenhouse gas. The potency of a greenhouse gas is commonly measured by comparing it to carbon dioxide which is deemed to have a “Global Warming Potential” of one. R-410A has a global warming potential of approximately 2,000, meaning that each pound of R-410A released to the atmosphere does roughly as much warming damage as a ton of carbon dioxide.

Refrigerant leaks are an important source of environmental damage and the EPA is engaged in rule-making which will effectively ban sales of heat pumps using R-410A after January 1, 2026 (banning new manufacture even sooner, by January 1, 2025). The specific terms of the ban will prohibit the use in heat pumps of HFCs that have a global warming potential (GWP) more than 700 fold greater than carbon dioxide. For mixes of HFCs, the GWP will be computed for the mix, not for the individual components. The rules will not apply to sales of used heat pumps (for example, those sold with a home). (For more technical background see Docket EPA-HQ-OAR-2021-0643-0066 at Regulations.gov.

EPA tailored its proposed limits to reflect the availability of substitutes. There are ready alternatives to R-410A, notably R-32, which has a GWP of 675 and so would remain legal under the new rule. R-32 is already heavily used elsewhere in the world (for roughly a decade in Japan) and many manufacturers see it as the successor to R-410. For examples, see these posts by Mitsubishi, LG, Carrier, Fujitsu, and Daikin North America. See also general discussions from achrnews.com (2019), achrnews.com (2020), and iccsafe.com (2022), all of which predate EPA’s latest rulemaking that would mandate new refrigerants — regulatory changes are moving rapidly.

The final rule is projected for release in September 2023.

Required building code changes

Ironically, R-32, the likely successor to R-410A is one of the two ingredients in R-410A. The other ingredient, R-125, is a so-so refrigerant and an especially bad GHG but a good flame retardant. The mixture of the two compounds makes an adequately-performing, non-flammable refrigerant which has an unacceptably high GWP.

Refrigerants are classified according to toxicity and flammability. For residential applications, we will want to continue to require non-toxicity (toxicity class A). But to allow pure R-32 and other lower-GWP alternatives to R-410A, we will need to accept refrigerants in a higher flammability class moving up from flammability class 1 (non-flammable) to flammability class 2L (mildly flammable). See also see this general discussion of refrigerant safety standards from the the EPA.

Moving to “A2L” — non-toxic but mildly flammable — refrigerants will require modifications to building codes.

EPA anticipates that states will adopt the 2021 revised versions of the International Building Code and the Residential Building Code that allows for use of several lower-GWP refrigerants that exhibit lower flammability (2L flammability classification). EPA understands that by 2025 building codes may be updated or updates will be under consideration which is relevant for some but not all of the potential lower-GWP HFC refrigerants and other non-HFC substitutes.

Federal Register, 12/25/2022

These code changes are likely to involve requirements for leak detection, circulating fans, labeling and handling instructions. Additionally, the new rules may limit the ratio of heat pump refrigerant charge (weight of refrigerant contained) to the size of the space it could leak into — one wants to avoid the possibility that a full leak could create an air mix with a high enough concentration of mildly flammable refrigerant to ignite. For a survey of code changes, see this EPA technical support document on building codes.

Legislation may be necessary in some states, including Massachusetts, to assure that delays in state building code changes do not interrupt heat pump installations.

Consumer Consequences of Regulatory Changes

Overall, these regulatory changes and related industry adjustments to heat pump products appear to be good for consumers. As manufacturers move to A2L refrigerants like R-32, we can expect an improvement in heat pump performance, perhaps 10% greater efficiency, meaning less electricity use, lower operating costs, and greater net environmental benefits. A quick survey suggests a range of results — ultimately, the performance improvements achieved will depend on careful engineering by the major competing manufacturers.

SourceRelative efficiency of R-32 heat pumpsComparison Base
International Journal of Refrigeration9% higher coefficient of performancesimilar R-410A system
International Refrigeration and Air Conditioning Conference at Purdue12% higher performanceR-410A in air to water heat pump
International Institute of Refrigeration2% higher COPR-410A
LGmore efficient other refrigerants
Daikinup to 12% more efficientR-410A heat pumps
Ex-machinery (a Daikin affiliated installer)20% more efficientR-410A heat pumps
Building Safety Journalmore efficient (A2L generally)refrigerants they replace
ACHR Newsover 8% more efficientrefrigerants they replace

The previous policy choice of less-efficient, non-flammable refrigerants was driven by safety considerations, but the consensus seems to be that we can address safety considerations with appropriate controls and rules. Consider that the new A2L refrigerants are much less flammable than methane and propane both of which we burn routinely within homes. Unlike methane and propane in homes, the refrigerants will not be routinely exposed to flame.

The new heat pumps will pose much smaller risk of leaks that harm the environment. They will contain less total refrigerant, they will likely be equipped with leak detection to comply with new safety codes, and the refrigerants used will have much lower GWP than current refrigerants.

For people who already have R-410A refrigerant pumps, the change does not create an imminent problem. However, eventually, R-410A may become scarcer and more expensive to acquire for the purpose of replacing leaked refrigerant. Note that one cannot retrofit R-32 into R410-A pumps. Ten years from now, if an R410-A pump leaks, an HVAC installer may suggest replacing the pump early rather than recharging the pump. HVAC industry observers see the switch as generating business for HVAC installers.

The likely 10% efficiency improvement expected from the heat pumps to be available soon will result in a considerably larger percentage increase in net greenhouse gas reductions in heat pump conversions from natural gas, where the difference between the carbon saved from reducing fossil fuel and the increased carbon costs of electricity generation is relatively small. For those conversions, the lifetime net GHG savings from a more efficient pump would likely exceed the GHG costs of a couple of years of delay. Those consumers who heat with gas who do not have an immediate need to replace a heating system may wish to wait for the better heat pumps. (For more math on this point, consider the simplistic pro forma at page 18 of this overview powerpoint: If, with a better refrigerant, the sample heat pump SCOP were increased to 2.5 from a currently typical 2.3 , this would pencil through to increase the net annual GHG benefits by 18%.)

The Longer View

Looking beyond the current generation and the next generation of heat pumps, there is room for further improvement. New propane-based pumps may offer even higher efficiency. See for example, Fraunhofer, Mitsubishi, Swedish Royal Institute of Technology. Of course, propane is highly flammable and it may not make sense to pressurize it indoors. However, we may eventually see safe, factory-sealed propane heat pumps that do not circulate refrigerant to indoor units. They will do all their heat pumping outside, heating a reserve of water or glycol which is then circulated indoors, conceivably through radiators. This would solve a huge problem for older New England homes that have hot water heat.

Return to heat pump outline

Published by Will Brownsberger

Will Brownsberger is State Senator from the Second Suffolk and Middlesex District.

25 replies on “Evolution of Heat Pump Technology”

  1. Thank you so much for this extremely helpful and informative post. I have shared it with the other Arlington volunteer heat pump coaches, and will mention its conclusions to my relevant coaching clients.

  2. Great, so the heat pumps being urged upon consumers today are already obsolete. If one has a leak like you had, and 410A is scarce or non-existent, the only choice is to start over. Equipment manufacturers are fine with this. I don’t know about you but having volatile refrigerants in my home make me a little uncomfortable. More reasons why Government making decisions by regulation is a bad idea.

      1. I just installed a two R-410A heat pumps and have no regrets. They will reduce my use of heating oil by over half.

      2. If it follows form with R22, then it will be available, but frightfully expensive. R22 is nearly 10X the cost of 410A and has been for quite some time. Units going in now with a 15-20 expected lifetime will be subject to those costs down the road.

  3. Thanks for this information, Will. One reason that I was thinking of moving forward with the heat pump replacement now is because of the advantageous state and federal rebates for installing whole-home conversions. I know that you don’t have a crystal ball and, thus, can’t see into the future. But based on your best judgement, do you anticipate rebates like the current ones available sticking around, decreasing, increasing, etc. over the next 1, 3, 5 years??? Grateful if you could weigh-in on this. Again, thanks for all your hard work on our behalf!

    1. I dare not speculate on the future of the state rebate programs. My own personal view is that the rebates are so high as to distort sound environmental planning decisions. But I do not have a sense of where the program is headed.

  4. Dear Will
    Thank you for this information and all you do. I will heed your advice about concentrating my resources in the meantime on improving my house’s insulation. Do you know where I might find objective information about pumped-in insulation for existing structures. I was contemplating cellulose because it uses recycled materials, but I wanted to learn more about whether this is a good choice. Are there concerns about mold and/or fire retardancy with cellulose?

  5. Regarding insulating your house to the max: folks may want to read Emily Anthes June 17, 2023 NY Times article Entitled “The New War on Bad Air”.

  6. Hi Will,
    Thanks for this informed analysis. I fall in the category of natural gas user that is looking to install heat pumps, and I’m thinking through your finding, “ From an environmental perspective, it may make sense for some homeowners, especially those who heat with gas and who do not have an immediate need to replace their heating system, to wait for the next generation of heat pumps.”

    In my case, I believe there are some environmental and financial reasons to move forward instead of
    waiting for the next generation of technology. To further the discussion, would appreciate any thoughts you have.
    1. Environmental Perspective: the heat pump will be replacing a currently eight year-old central air conditioner that also uses R-410A. It’s running fine, but it has the potential to leak (or leak more) as it gets older. Maybe a higher potential than a new heat pump installation?
    a. Should I consider the net increase, or decrease, in refrigerant leaks (if any)?
    b. Would making a simple assumption that the probabilities of leaks (HP vs. AC) cancel out be OK, thus there is no net increase in GHG due to refrigerant leaks?
    c. Did you consider the reduction in leaks from retiring and replacing old air conditioners (central or room) that are no longer needed in your assessment?

    2. Cost Premium on new technology: given your description of the new technology, codes, etc.. it seems like there should be a sizable cost premium on the next generation of heat pumps.
    a. Would additional upfront costs negate savings from the higher efficiency?
    b. Also, two installers say they can use my current refrigerant lines, rather than replace them (and tearing up parts of the house). It doesn’t sound like I can use the existing refrigerant lines with the new HP’s and new refrigerant.

    Thanks for any thoughts,
    Dave Beavers (in role as a Belmont homeowner)
    For transparency: also, Chair – Belmont Municipal Light Board

    1. HI Dave, these are good questions and I’m not sure I can advise you, but here are a few thoughts:

      1. I don’t know that leaks are more likely to happen later in life. I have not seen data as to when leaks occur and I think it would be hard to collect that data — installers don’t like to talk about leaks. I wouldn’t consider a change in leak probability as a factor in your decision. It’s too uncertain to count. One thing to consider is the retirement process — does the de-installer properly recover the remaining R-410A.
      2. I generally don’t encourage people to weigh annual financial savings beyond the first year or two as a factor in heat pump decisions — there is so much price uncertainty.
      3. Not sure whether the new pumps will be or more or less expensive — yes, they will have some additional safety devices, but the new refrigerants allow them to be smaller.
      4. I have no wisdom on whether lines could be reused.
    2. As someone in the trade I’ll offer this:
      As systems get older they are more likely to leak.
      The likelihood of leaks from conventional AC or HP will be the same.
      Prices on equipment, conventional or heat pump, are continuing to rise. You can assume that next year prices will be higher than this year.
      Savings from additional efficiency may or may not pay back – that will depend on the cost of electricity.
      You “may” be able to use your current lines. There are flush kits available for transition from R22 to R410A. One can safely assume that will be the case for transition from 410A to newer refrigerants. That being said, we always try to replace lines as it is just another spot where age will eventually cause a leak. From an installer and customer perspective it’s easier to do it at the time of installation, rather than down the road when and if it happens. The environmental impact doesn’t help of course.
      As an aside, the continued changes will impose challenges on the ability to repair these systems. Particularly with circuit boards and components, availability is sketch and constant changes and upgrades makes it impossible for a service provider to have every iteration instantly available.

  7. LOL. I just got a $46K quote for heat pump install on a sub-2000 s.f. house with ducting already in place. (There are 2 systems because that was best/cheapest option when installing AC needed for medical reasons in an old home.) Forty. Six. Thousand. A single would cost half that in houses that already have ducts and central AC in the basement. According to the contractor the new systems will be MUCH more expensive, I’m told, because of all the additional safety gear required.

    I want to ask people who cook up these utterly implausible pointless schemes: What color is the sky in your world?

  8. Can you say more about what you mean about high rebates distorting sound environmental planning? Thanks for all the useful info.

    1. The cost per ton of carbon saved in conversions from gas is often over $1000, while the Biden administration estimates the damages from carbon emissions at $190. In some cases (not all) people are installing heat pumps where they might do more for the environment by spending the same money on home energy efficiency measures like insulation, etc. I say might because the environmental value of insulation projects depends heavily on where the home is starting from — some homes have already been fully insulated.

  9. Leaders of the HeatSmart Alliance, ZeroCarbonMA, and Green Energy Consumers Alliance are opposed to pausing heat pump conversions of natural gas systems. We need to be accelerating electrification, not slowing it down.

  10. Thank you Senator Will for such a comprehensive discussion of the Evolution of Heat Pumps.
    We have 2 years ago fully insulated our home. Based on the recommendations in your discussion, we will wait a couple of years for the new heat pumps to be available in the market.

  11. Consumer Consequences of Regulatory Changes: R-32 may be inherently more efficient compared to R-410A, but that does not mean that heat pumps using R-32 will be more efficient than heat pumps using R-410A. Manufacturers design heat pumps to achieve efficiencies based on market demand. Key efficiency drivers are regulations and incentive program requirements. Absent any changes in regulations and incentive program requirements, manufacturers that are switching to R-32 may lower production costs (for example, by making heat exchangers smaller or using less efficient compressors) so that they match current product efficiencies. They will not be constrained to improve heat-pump efficiencies unless market forces dictate otherwise.

    1. Agreed that we can’t be sure how the market will move. But I do think the statements from manufacturers are encouraging. Daikin is already publicly claiming a 12% efficiency improvement. See the links above.

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