A missing number in the heat pump conversation

I’ve recently heard some anecdotes about people who have fully replaced their fossil heating system with heat pumps and not achieved energy savings — in other words, they are using as much energy in the form of electricity as they were previously using in the form of gas.

How could this be? Heat pumps are generally more than 200% efficient in the sense that the energy (measured as heat) that they pump into the home is more than twice the energy (measured as electricity) that they consume while pumping. We would expect most people to at least achieve some raw energy savings in a whole-home conversion, even if they do not achieve financial or greenhouse gas savings. While I have written a lot about all-too-frequent refrigerant leaks, the majority of installed heat pumps do not immediately leak and refrigerant leaks cannot be the explanation in every case of low energy savings.

The explanation may be that some people are actually using more heat in their home after they install heat pumps because the heat is not well distributed. The distribution of heat is hard-to-measure variable that I’ve heard discussed as a comfort issue, but it may also be a critical performance variable. Heat distribution issues could reduce energy savings in several different ways.

In the absence of a duct system, a heat pump conversion uses wall units for blowing heat. However, it is usually prohibitively expensive to install independently controlled units in every room, so the wall units are usually installed in only some rooms. It may be necessary to overheat the rooms that do have units to assure that adequate heat reaches the rooms that do not have units. This is especially true since heat pumps can be used for both air conditioning and heating. The choice of where to install wall units involves some difficult judgment calls — the rooms that need the most air conditioning are not necessarily the rooms that need the most heating.

In one striking case, I heard from a constituent who had post-conversion electric bills over $1,000 per month during the first winter. They had done a whole home conversion in their single family home and had installed wall in units in some but not all of their rooms. My staff and I visited and interviewed all occupants of the home. It turned out that one parent was using electric space heaters to keep warm in their downstairs work-from-home office, which the wall units did not reach effectively on winter days, while the teen-age son was sometimes turning on the wall unit in his bedroom as an air conditioner on winter nights. They had also added electric baseboard heat to keep their partially-finished basement warm — the basement previously benefitted from the waste heat from their fossil boiler and exposed radiator pipes, but post-conversion it was chilled by their heat pump hot water heater.

Even when the home has a pre-existing duct system that can be converted for use by heat pumps, that system may or may not be efficient for distributing heat. In my family’s conversion case, our pre-existing duct system was modern and had been used for both heating and cooling. It served just fine after our heat pump conversion: The directly metered operating efficiency of heat pumps correlated closely with the before and after energy use results — suggesting that heating usage had not changed dramatically overall. However, when a pre-existing duct system is older and previously used only for air conditioning, it may not function as well for heating.

Consider the conversion of a home that is heated by radiators in most rooms but has a ducted system for distribution of cool air. When the home conversion disconnects the radiators and instead circulates heat through the ducts, several problems may emerge. First, the balance of the air conditioning system (the pattern of some vents blowing more air than others) may favor rooms that need air conditioning more than heat, with the result that those rooms will be overheated in winter. It may or may not be possible to rebalance the system without expensive resizing of the ducts. Second, the duct system may be somewhat leaky or may run through areas that are cold in winter and there may be substantial heat loss through the ducts. Finally, and this dynamic can affect both ducted and ductless systems, hot air rises: so as air flows out of vents located high on the walls (ideal for air conditioning), rooms may be overheated near the ceiling.

Of course, heat distribution may be far from optimal before conversion — we’ve all seen buildings (usually larger buildings) with windows open in the winter. Whole home heat pump conversions have been few in number until recently. As we begin to see population-scale studies comparing energy use before and after whole home heat pump conversions, we will get some indication of how significant heat distribution issues may be from a policy perspective. But we have already enough anecdotes to know that the question is of interest.

Please share your experiences and thoughts as comments below!

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Published by Will Brownsberger

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

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  1. I had heat pumps installed in my house, 2 units on 1st floor and one in the finished attic. Unfortunately, the 1st floor bedrooms did not receive heat from the mini split installed in dining room. Therefore, every night at 8:00 PM during the winter, I had to turn on the oil boiler to heat up the 2 bedrooms. I turned off the heat pump at the same time. I was assured by the installer that the 2 bedrooms would be warm with the heat pumps. NO
    Overall, very disappointed with the end results

  2. We had mini-splits installed in our home for air conditioning purposes. The air flow from them is really not even enough to use for heat in winter. I will not be giving up my gas-burning boiler until there is a heat-pump solution for hot water heating systems. Convective/hot air systems just cannot replace the comfort of radiant heat.

  3. i have had splits for years in two different locations… the heat distribution is an issue…with my forced air oil system, heat is pretty evenly distributed… with the splits there are cold area’s in the house where there are not splits… I have been spending over $ 1200 a month on electric and oil… i have not experienced any savings.

  4. We have had a heat pump for several years in the kitchen (wall model), it had been cold in the winter despite two radiators there, now it’s fine, I can regulate the heat with a remote–and it gets warm now, and in the summer I use the heat pump to air-condition the kitchen. Plus, we got rebates for our heat pump and installation (I can’t remember the exact amount, but it was substantial relative to the cost) .

  5. We have experienced a lot of problems with the heat pump system installed in our old, hard to fully insulate house. The high wall units tbat were supposed to transmit warm air to two rooms did not reach acrooss tbat expanse, ultimatel requiring that another compressor had to be installed.At the contractor’s expense. We have found that the 3 units installed lower in the wall close to floor level are much more efficient at generating warmth than the high wall units. Overall our bills were higher this heating season than before. Eventually the system worked better after constant tweaking, but it has been much less economical or efficient than we had been led to believe. One tip that helped improve performance was to avoid radical changes in the temperatue settings between sleeping and waking hours, as the system uses a lot of energy when called upon to increse the temperature by more than a few degrees at a time. That is diffferent than our practice when relying on gas forced hot air.

  6. Dealt with splits for years (not heat pump, but that’s not relevant for circulation). They work well in new open concept construction. They do not work well in houses with multiple small rooms (old New England houses but also new construction with multiple bedrooms/offices/etc.). An HVAC guy told me to memorize this sentence: Air does not turn corners.

    Speaking of HVAC guys, this trade is well known as one of the most corrupt. Thanks to lobbying, the state often facilitates this corruption (e.g., allowing “technicians” to red-tag perfectly good furnaces after a fake “camera” inspection). The HVAC sector can’t handle existing demand now. The state needs to ensure a larger qualified labor supply as well as much better business practices before forcing even more interactions with this execrable industry.

    1. Steve,
      As an HVAC/Oilheat contractor I’ll take exception to your blanket characterization of the trade, but will agree there are a lot of bad actors and folks with nowhere near enough expertise to do the work. We deal with fixing work done by these entities all the time. If you haven’t noticed, many of these hacks have jumped into the heat pump realm, as they are simply following the (government and utility/Mass Save) money. They have zero experience and expertise and you can be sure they will not be around for follow-up repairs on equipment that is difficult or impossible to repair by design. Think long and hard before a conversion.

  7. Just yesterday I had an informative interview with a fellow from the mass save program. She showed me a table that estimated that if I replaced my current natural gas forced hot air furnace with a whole house heat pump my energy costs for heating would double. This is not a distribution issue. It turns out that natural gas is still the cheapest option to heat a whole house.

  8. I just had whole house mini split cold climate heat pumps installed in mid-February in my two family. One system for the other apartment and one system for mine ( So two outdoor units, and four air handlers in each apartment). It’s multi-zone, we can control temperature for each handler. I and the folks in the other apartment have loved them, even more than I expected to. The aspect that most impressed me was even and constant heat distribution across all rooms. So I haven’t had any problem with that. My contractor was very detailed in doing calculations and discussing options for me for placement and how heat would distribute. As far as using more raw energy, because they are so new, I can’t really compare them yet to last year when I was using steam radiators. But the bills so far have been somewhat lower than I feared. I’ll have a much better idea come next January. I mostly follow the ” leave it and forget it” advice on setting the temperature. Some say that’s supposed to be more efficient, and others say it’s not. Maybe that might explain higher energy use? With my steam radiators I would turn the furnace all the way down at night, so it wouldn’t come on at all. Then start the furnace up in the morning. Now I leave the handlers at 65, 63 in the bedroom. Still, it seems that even on the coldest night s (we had a couple 14 degree nights after installation), my air handlers only come on for a bit. So they seem pretty darn efficient to me.

  9. Agreed that distribution of heat from heat pumps is not as good as from baseboard heating, at least in our house. I think we are achieving small energy savings – certainly not large savings. From a purely financial perspective, moving to heat pumps made little sense in our case, but we had that suspicion going in to the project. We did it mainly to stop burning fossil fuels in our house (our boiler and oil tank have both been removed). Also we had only room air conditioners previously, so it was a great benefit to get central air conditioning from our heat pump system.

  10. MassSave says that heat pumps cost more to run than gas heat. This is without regard to distribution issues. I think the main reason is that the efficiency of heat pumps is calculated according to the amount of electricity used, but not according to the amount of heat used at the power plant, whether it is fossil fuel, nuclear, etc. A typical gas power plant wastes 40 percent or more of the heat, by throwing it off to the air or water. Plus there is a smaller amount wasted in transmission, even if it comes from a renewable source

  11. I do not have heat pumps, but can shed some light on comparing the costs of energy use from gas vs. electricity. I keep detailed records of my gas and electricity use and their costs (I live in Belmont). Taking the total costs and dividing by the total energy delivered for 2023, I get $2.17/therm for gas and $0.2574/kWh for electricity. My gas furnace is 83.7% efficient, so 1 therm (100,000 Btus) will deliver 83,700 Btus of heat for $2.17. For a heat pump to deliver the same amount of heat, I need 83,700/(3414*COP) = 24.5/COP kwh, where COP is the heat pump coefficient of performance. The COP I need to break even with the gas furnace cost is calculated as follows: $2.17 = 24.5/COP * .2574, yielding a COP = 2.9. Unless you have a ground source heat pump, your COP averaged over the heating season will be less than 2.9. That means, all things being equal (like heat distribution), substituting a heat pump for a gas furnace will increase one’s heating bill for the fuel prices I see in Belmont.

  12. We converted from a hot water system with an oil furnace to heat pumps with a new duct system. We love it – very well-controlled temperatures. Based on a year of bills – we are spending about the same or a bit less than we would if we had stuck with oil. Prior to the conversion, we used roughly 1000 gallons of heating oil (hence about $3500 – $4000) per year and had average electric bills of $150 – $200 / month. Hence about $6000 per year on energy. In the past full year, we spent ~$5000 on electricity and less than $500 on heating oil (the water heater is still on the furnace). We kept the furnace just in case – as we live in a rural area of Boxford that does suffer from outages. The new heat pump water heater will be a welcome addition in a year or so.

    Our system was very expensive but very well-engineered – so no issues like you noted above. It is also astounding that the costs are less – given the outrageous electrical costs (We are currently at $0.38/KWh). We are building a new solar array with 25 – 30 panels – an investment in the future and in slowing climate change.

  13. Fascinating, and depressing, because it seems more and more certain that air source heat pumps are not going to help reduce energy use much. Geothermal heat pumps might, but only if they can feed our ubiquitous existing stock of radiators with steam or hot water. That would (at least) address the distribution issues Will and others describe here, since old-fashioned cast iron radiators are designed to be modulated individually using a valve on the inlet side (if, of course, you remember to exercise it twice a year so it doesn’t corrode solid). I think (anyone?) that a residential geothermal heat pump could produce hot water, and I think I toured a big one at a private school years ago that made steam. But individual residential geothermal systems can be difficult to install even in the suburbs, and impossible in a city. I have heard, though, that MassSave has rebates for the former now, and that some cities are experimenting with neighborhood or street by street geothermal networks that, perhaps, could re-use existing gas lines. I look forward hearing more about both.

  14. The distribution problem is certainly evident in our 6 year installation. We do increase the temp. setting a few degrees and wear sweaters. We have also tried running the ceiling fans and portable floor fans to circulate the heat better, to mixed results.

    In the summer, using the dehumidify setting works extremely well to cool the entire space.

  15. We had mini-splits installed in 2019 or so. Our house is a standard Belmont side-entrance colonial. The company installed one wall unit in the DR and one in the sunroom for the first floor. Nothing in the LR. Based on the volume and the output of the unit in the DR, the LR should have been fine. The DR unit also had to cover the kitchen, which is open (no walls in between).

    Well, the DR unit faced the kitchen, so it did a reasonable job of heating/cooling there. But there was no way that air was going to get to the LR, because it was blowing in the wrong direction. So we had to put a fan on the DR table to get any cool air into the LR.

    That got annoying, and it wasn’t efficient, so we had to add a new outdoor unit and a new wall unit. It wound up being much more expensive that way — if they’d thought about it more, they would have put in the LR unit on an outdoor unit with greater capacity.

  16. Some should try heat pumps (I have). Some should not. But rather than rely on the Massachusetts government, each person should find what works for him. Note that the Federal Government complicating the problem by issuing regulations that will change the economics of air conditioning and heat pumps.
    The Soviet Union failed in central planning, how can we expect the U.S. and Massachusetts to do better?

  17. Our house was built in 1998 with gas central heating and with AC (using the same ducts). We had heat pumps installed about 1 1/2 years ago when our gas furnace died but we also replaced the gas furnace to use as a backup (which is almost never used – probably because of the relatively mild winters the last couple of years). Our gas bill went way down but our electricity bill went way up. I would estimate that together, we pay about the same as we did with the 1998 gas furnace. And the rooms don’t heat up nearly as quickly as they did with the gas furnace. What used to take about 10 minutes to show a rise in temperature of a few degrees now takes 1-2 hours. (The gas furnace only kicks in if we raise the thermostat more than 5 degrees above the current temperature.)

    Let people figure it out on their own. Maybe someday it will be obvious that all electric is the way to go but it isn’t now.
    I live in a condo with 11 rooms including bathrooms and basement that are all heated and cooled, 3 of the 11 are heated with electric. The cost to heat those 3 rooms per month alone cost double what it costs to heat the other 8 rooms with NG.

  19. We added mini splits in late 2022 and I’m so glad we did. I think our house is the perfect type for mini splits to work well. We have a side by side duplex so only needed one compressor outside to cover our side. We also met with a few companies who all recommended slightly different configurations. The company we chose required fewer units and I believe had the better plan. We have a larger unit in our living room that mostly heats the entire first floor. The kitchen is a little chilly but not unlike many apartments I lived in where there was no heat source in the kitchen aside from the stove. Most of the heat also goes upstairs and into the closest 2 bedrooms to the stars if the doors are open. It actually gets hot at night and we have to turn the temperature down. The farthest bedroom still gets some heat but that room’s unit needs to be turned on at night. When we are downstairs we do also turn on our ceiling fan in the living room (going the opposite direction) to keep some of the heat downstairs. Our electric bill is higher and I don’t believe we are saving money from when we used only gas. However if we could get solar I think we would be saving a ton of money. Both my mother and sister have solar and mini splits and hardly pay anything for their heat/cooling. I’d love to know more about assistance for solar purchase/installation locally and where that fits into this discussion.

  20. My husband and I have wanted to be proactive in replacing our 25+ year old gas furnace and AC unit before they broke. After a great deal of research and help from Abode EM through Belmont Light Department, we made the jump, but kept our gas furnace ‘just in case’. . We live in a cape..so 2 bedrooms on the first floor, one on the 2nd, and a finished basement.. We felt that mini-splits would not work because there were too many living/sleeping places that would be cold.. and we didn’t want them hanging on every wall! Luckily (?) we had an existing ducted AC system (25 years old), we had 4 different companies give us proposals. When they came to do the estimate, we told them that we needed to have the ductwork inspected to be sure it would be adequate for heat and could deliver the heat throughout the house. The company we chose had an inspector come..”Yes! Great news! You’re good to go..will work great” ..so we had the air source heat pump installed for floor 1 & 2, tying in with the existing ducted AC.. we put a mini split in the basement, knowing that without the gas boiler on, it would be cold..BUT we don’t use the basement except when grandkids come.. but the washer/dryer/ and a bathroom are down there as well.. the basement has worked great, as it stays around 53-55 on the coldest days with. the mini split off.. , and easily heats up when needed.. BUT even when the heat pump for floor 1 &2 was on 24/7, the 1st floor could not get above 62 degrees.. HMM.. a call in Jan to our installer.. First thing, they installed a new thermostat in case the previous one they installed was faulty.. It was not the problem, so then they re-inspected the ductwork.. seems in about 5-6 of the AC ceiling vents, there was no or little airflow.. .. so no heat.. and in a cape with no real attic, and old metal ductwork, replacing is EXTREMELY difficult and costly.. BUT,one of their technicians had a plan and could figure out how to carefully remove the old ductwork and put in all new.. he took it as a challenge.. but the work would be prohibitively expensive. It took a while for us to have them all agree to replace the ductwork at no expense to us as we had the emails of the ‘GREAT news’ on the original inspection prior to installation.. We felt their inspector was at fault in not doing a careful inspection..some of the ceiling vents were not even connected to the system?? 3-4 men worked all day for 4 days removing and replacing all the old existing ductwork.. that was finally done this March.. and now, when needed, we can feel heat coming from all the ceiling vents.. we have yet to go through a cold winter.. but feel so relieved to have the vents all new.. we did not remove out 25 year old gas furnace as it heats the water, so we have it for backup.. not sure when to do if/when that fails.. so that’s our story.. we have our heat pump thermostat set to 64 during the day (from 6AM onwards) but then down to 60 at. 4 when the ‘time of use’ expensive rates kick in. Yes, we dress in. many layers, and can bump it up when we have company, but we feel better not burning the gas…. So check your existing ductwork carefully before proceeding to whole house heat pumps.

  21. Thanks for this informative post. We installed heat pumps two years ago (primarily to use as ACs in the summer as we just used window AC units before) but we are trying to use them more in the winter instead of our gas furnace. However because we elected 100% renewable energy (through Watertown’s municipal aggregation program), we find the cost to be higher than using our gas furnace. So currently we are using the heat pumps as the weather just starts to get cold then switch fully to the furnace around December. We do also rely on the furnace to maintain somewhat reasonable temperature in the basement (no heat pump unit there). To help with the distribution, we try to be thoughtful about which units we turn on and closing doors to rooms we are not using much. Overall we do love the heat pumps aside from the costs. The only minor complaint is that in small rooms the hot air can feel very drying compared to the furnace.

  22. Caveat: I’m using an oil burner with forced water.
    My understanding is that replacing a gas furnace with a heat pump should work better than mini-splits. It seems like we are mostly talking about mini-splits here, right?
    I’m also investigating a central heat-pump to forced water. It is early in development, and I’m not so sure that it is going to prove viable. See 2040energy.com for some details.

  23. Thank you to all who have shared thoughts above. Lots of useful examples.

    The comments help underline that the distribution problem is likely greatest in older homes. With many smaller rooms, as opposed to an open floor plan, heated air will not circulate as well. Additionally, the older homes are likely to be less insulated so (a) some rooms may lose heat fast and get much too cold if they are not near the heat sources; (b) the overheating of other rooms to compensate will lead to high energy loss from those rooms.

  24. Overall, 5 heat pumps have provided decent heat for 950 square foot condo. Installation was sloppy unfortunately but after many repair visits from Homeworks, the system is working.

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