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We currently have a central AC unit and oil furnace. The AC is broken and the furnace is old, so we are thinking of replacing both sometime in the next year.

We are considering replacing the AC with a heat pump and the oil furnace with a gas furnace in the hopes that the gas company will bring a line down our street from the main road sometime before the furnace needs to be replaced.

From my understanding, the heat pump could also be used to heat the house up to a certain point in the winter.

I don't know a whole lot about heat pumps, so I'm wondering how effective a heat pump would be at cooling and heating the house (currently just the first floor, about 800 sq ft, and basement), both in terms of cost effectiveness and actual comfort level of the house. Should a pump be able to cool our house on 100+ degree days to, say, 70-75 degrees? Will it be able to get our house warm enough in the winter in a reasonable amount of time?

I'm told the units will somehow be set so that the furnace kicks in automatically when needed, but I'm wondering how that is actually determined. I don't want to be sitting in a cold house for hours waiting for the furnace to realize the heat pump isn't going to do the job.

I've also heard the pump is cheaper for heating, but I am wondering about the specifics. How much cheaper would a heat pump be to run? Both run on electricity to some extent, but does the heat pump use more electricity to warm the house than the furnace, and, if so, is it enough to make up for the cost difference?

Any other pros/cons I should be thinking about?

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  • A ground-loop heat pump is very efficient. So if that's the route you're thinking of going, definitely a good choice. However, I assume you are maybe talking about an air source pump, which is less efficient. It will work, but won't be very efficient when the temp gets too low (and may not be the best for your sole source of heat if you have extremely low temperatures). For A/C, though, it'll be just fine (as it is, in essentially, a big A/C unit.)
    – DA01
    May 1, 2013 at 18:54
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    Oh, and as for cost, the electricity runs the fan (just as any furnace) and the compressor pump (to extract the heat). In terms of total energy costs used, it's a lot less than a fuel-based heating source as none of the energy sources you are paying for are being used to heat the air. Essentially, you are getting the heat for 'free' but still paying to extract it/circulate it in your house.
    – DA01
    May 1, 2013 at 18:55
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    I am not going to try to compete with the long winded answers below, but gas is cheaper for heat in at least 3 of the states I have lived in. In Oregon for example a ~3000 as ft home cost over 500 per month with electric heat. I changed to gas and cut the price in less than half, I later changed to a heat pump and for most months my bill reduced even further, but when the temps got below 27 degrees my system at the time switched to electric heat and my bills doubled. Today I live in a smaller home but today's split systems are efficient down into the teens some lower. It depends on the system
    – Ed Beal
    Dec 1, 2018 at 2:24
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    @EdBeal: Heat pumps are HUGELY more efficient than resistive heating, though that advantage decreases at lower temperatures -- to the point where they may indeed cost less to operate than gas, oil, or wood pellet systems. I have a high efficiency gas furnace driving FHW; switching to heating with the heat pumps seems to have reduced my total energy usage considerably. Your mileage may vary; Boston isn't exactly Canadian temperatures most of the time but isn't exactly Georgia either. Of course I did improve wall insulation at about the same time, but the spreadsheet is still sorta impressive.
    – keshlam
    Aug 11, 2023 at 22:01
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    @keshlam I basically said the same thing, with the problems with heat pumps not working well at - temps to the point an emergency heat source other than the heat pump is needed, once it gets below the operating temp the heat pump just don’t work,no matter how efficient , then restive, gas or wood burning heat sources are needed. Since I posted this in 2018 I have seen the operating temperature of several brands drop 10-20 degrees F.
    – Ed Beal
    Aug 24, 2023 at 16:31

7 Answers 7

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Heat pumps are quite common in Central Oregon where summer daytime highs are often over 100°F and nights below 25°F. I have been in many a heat pump rental house in winter at below 10°F in a wide range of efficiencies from below eight to over 20 SEER. They work fine.

For units with a SEER of over 14 or so, the backup heat does not kick in (except for defrost cycles) in cold, dry weather and the thing pumps a lot of heat into the house with air register temperatures over 110°F. These are all air source units—there is no groundwater in the desert. Natural gas is available and cheap, but about half of the owners choose heat pumps, the remainder choosing central air plus a gas furnace. The recent trend seems to be favoring heat pumps more.

A close friend had a ground source heat pump installed in his Willamette Valley home (temperate, moist climate). It was beautifully quiet, compact, and tremendously efficient. When I asked if he would do it again, he said "No. The expense of excavation would not pay for itself in his lifetime." (He was about 32 at the time). For a level lot in nice sandy loam with the water table about 6 feet deep and good water flow from 2 feet deep and below, it cost $45,000 twenty years ago just to install the ground loops. I can't imagine what it would cost now.

I'm told the units will somehow be set so that the furnace kicks in automatically when needed, but I'm wondering how that is actually determined.

I have owned two heat pump systems (okay three: one was an upgrade replacing another). Backup or emergency heat (same physical thing) is activated under any of several conditions:

  1. During defrost cycles—which only occur during system "heat" operation. The heat pump outdoor fan is turned off, the system reverses to cooling mode to melt frost and ice built up on the outdoor unit. To keep from blowing cold air indoors at a time heat is expected, the backup heat is turned on to remove the chill. My most stupid heat pump, a 1980s relic, used a timer which ran a defrost cycle for 4 minutes out of every 45 minutes (of system "on" time) whether it was needed or not. The other two systems were much smarter and learned under what conditions defrosting might be needed, would engage defrosting every hour or two, somehow detect if it wasn't needed and return to heating within a minute. Otherwise the defrost cycle could run up to 3 or 4 minutes.

  2. When the thermostat (which are necessarily specialized for heat pumps) is switched into emergency heat mode. You would do this if you did not want to run the heat pump because a tree fell on it or something.

  3. When a simpler thermostat's setpoint is more than 4°F above the current room temperature, or when a smart thermostat determines that the heat pump is not going to get the temperature to the setpoint anytime soon.

I've also heard the pump is cheaper for heating, but I am wondering about the specifics. How much cheaper would a heat pump be to run? Both run on electricity to some extent, but does the heat pump use more electricity to warm the house than the furnace, and, if so, is it enough to make up for the cost difference?

Yes, a heat pump uses more electricity than a furnace, which only blows air inside. A heat pump blows around air outside and inside, plus it runs a hefty refrigeration compressor. The seasonal energy efficiency ratio (SEER) is a measure of how much heat is moved compared to how much energy was input to move the heat. An electric furnace or electric baseboard heater would have a SEER very close to 3.8. A new window air conditioner is now required (in the U.S.) to be at least 8.0, and for an Energy Star rating, at least 14.0. Ratings of 10–12 were recently common in low end heat pumps, but the required minimum is 13.0 since 2005. As the rating increases, so does the purchase price.

My Portland, Oregon, condo came with an electric furnace. When it was installed in the 1970s, electricity cost 2.2 cents per kilowatt hour; today's price is $0.07–0.11 depending on the power company. During a particularly cold winter storm c. 2004, my electric bill made it to $300 per month, mostly due to some compromised windward windows—normal winter electricity ran $50–70. I replaced the electric furnace with an 18 SEER heat pump costing $7,000; a 15 or 16 SEER version was $5,000 IIRC. Afterward, my electric bill was $45 in normal winter weather and up to $60 in severe cold, most of which was probably to run a bank of five computers 24x7. While the economics may not make perfect sense, I am sure the more "normal" electric rates which most areas have would easily make the break-even point plenty soon enough.

I am really happy with having a heatpump. I would consider doing a ground source if there were a cheap way to bury the tubing, but otherwise the air source is just fine.

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You don't have to worry about a heat pump being inadequate for cooling tasks, they are available in a large range of sizes. For really large buildings, they can be ganged together. 800 sf is a walk in the park for residential sized units.

I don't know the specifics of what determines when the backup furnace kicks in. IIRC, it is the combination of a lower thermostat set point and the outside temperature. It kicks on when the pump is not keeping up or it's too cold for it to run efficiently. I can assure you you will not be sitting for hours waiting for backup heat. No customer would sit still for such a system.

While it is true that heat pump heat is free, you are just paying to move it around, if you've had heat wave cooling bills before, you know moving heat around is far from cheap. Only a careful analysis of the various options, considering both operational and installation costs, as well as life cycle replacement, can you make a proper decision about which system is most cost effective. The correct solution will vary by small changes in energy costs and climate.

In cold climates, a ground heat source system should at least be considered because it will reduce or eliminate the need for backup heat. If you are concerned about your carbon footprint, do not forget most electricity generated in the US is by burning fossil fuels. Your footprint from using a heat pump will vary greatly depending on where your local power is coming from. Heat pumps make a lot of sense for many people, especially if they are investing in cooling equipment anyway. But everyone's situation is unique, so the best solution can be arrived at only after careful rational analysis of all the factors.

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    Even if your electricity comes from burning fossil fuels, the efficiency of a heat pump can't be beaten because they are over 100% thermally efficient. Something around 300% efficiency is common, so it's more efficient to burn fossil fuels at a power plant including losses at the plant and in the line, and run a heat pump than it is to burn fossil fuels directly for heat in your home.
    – Vectorjohn
    Mar 13, 2019 at 22:57
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We had a heat pump in Pennsylvania , 1 hour north of Philadelphia, used for heating and cooling. We now , after 25 years in that home we built, have gas forced air and a central AC unit. There is no comparison. The gas heat is cheaper, stays I the room, and feels warmer. I was always cold with the heat pump, even when it kicked on to residence heat . The heat pump only provides cheap heat until you get to temps of below 32 and then it becomes less efficient and more expensive. If you can get gas heat, by all means do it. We had oil in our first home, summer /winter hock up and even that was better than the heat pump in Pennsylvania. South of Philadelphia , with milder winter temps is better for heat pumps no matter what he contractors and electric companies tell you.

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How well the heat pump warms the house depends on the capacity of the heat pump and how well insulated the house is.

Heat pumps definitely act a lot slower than furnaces, the temperature just kind of creeps up. In fact, in my house in New Hampshire, the temperature actually gets lower when the heat pump comes on because it starts blowing cold air around for 10 minutes.

The way backup heat works in my house is that if the temperature gets 5-degrees lower than the thermostat, then the furnace comes on. Once the temperature gets to be about freezing, the heat pump is more annoying than helpful. During the fall and spring when the temperature is in the 50s and 60s, the heat pump is very useful because otherwise the furnace would be coming on and off all the time.

As far as efficiency is concerned, it is definitely cheaper to run the heat pump when the temperature is above 45 degrees. Also, a heat pump is a lot cheaper than an air conditioner. Of course, with some $15,000 heat pump it can take a long time to justify that even if you are saving $100 a month.

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Nota bene: I realize this is an old question but I thought I'd add an answer since this question was recently bumped and there's apparently been recent interest in the topic.

Here in the Midwest, and I believe much the same applies to New England, heat pumps would be sized for the desired summer cooling capacity and you just kind of get what you get for winter heating capacity. If there's snow on the ground every winter then building codes likely require some kind of backup heat to any heat pump. I know people will want to argue on if this is necessary given recent advances in heat pumps but building codes are written in blood so good luck on getting that changed any time soon.

If the desire is to get rid of the oil furnace and leave open the option for natural gas later then look into a furnace that is compatible with LPG and natural gas. LPG from a tank isn't always exactly cheap, and there's likely building codes involved there too, but it would likely mean leaving a minimal cost transition to natural gas heat. I've seen furnaces that are built for LPG but come with a natural gas conversion kit, and this conversion kit is often tossed out by the installers. Save that kit if it's there.

There's a reason electric resistance heat is not all that popular, it is cheap to install but very expensive to run. A heat pump will mean not needing electric resistance heat for the entire winter but for New England you'd likely be using that resistance heat for far more than you'd like. There may even be local building code that doesn't allow resistance heat without a fossil fuel furnace. Putting in a natural gas furnace without any natural gas service (yet) isn't likely to fly past the inspector's radar.

There's not likely anything against putting in resistance heat but there's not likely to be any cost savings in doing so. If the heating capacity calculations show the required electric demand exceeds the supply to the home then that's an added expense and/or some kind of building code hassle.

I have a heat pump and calculating the costs versus natural gas has so many variables that it is difficult to tell if I'm saving any money. For some people the calculations will be far simpler and/or with quite obvious results. The point is that I doubt anyone would be able to determine if there is a cost savings with the information known so far, and it could take a lot more information to figure this out for the calculations to be moot the next year as electrical and fuel fees change.

Oil heat isn't really a thing around here but I understand oil heat is still popular in New England. Oil heat has been there a long time, running natural gas can be difficult with all the hills and such, and conversion to LPG can raise concerns with little old towns of homes packed in tight since a pressurized tank of LPG can be a hazard to neighbors in a way that an oil tank is not. There's a lot of wide open space in the Midwest, we can plant those LPG tanks well away from any occupied structure.

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  • Interesting. I last had a heat pump system in an apartment I was renting in PA back in the '90's, and I had almost exactly Sue's experience (but a bit worse). Its now 1 decade later for her, and 3 decades later for me, and I get a lot of people telling me they are much better now, even better than gas. I'm skeptical. You don't easily forgive a system that leaves you cold and with August-level electricity bills in the winter.
    – T.E.D.
    Aug 24, 2023 at 22:15
  • I'll see claims that heat pumps are good enough now to not need any backup heat, even in cold places like Minnesota. Experience tells me not to believe them, and even if I did then building codes are not likely to allow a heat pump without a backup. Looking into fireplaces and electric wall heat units I find they are not likely allowable as backup heat, they are only for "supplemental" heat. Putting in a fireplace to make a space look nice and feel comfortable will help but this is not likely to circumvent building code requirements for a proper furnace. YMMV, of course.
    – MacGuffin
    Aug 24, 2023 at 22:51
  • @MacGuffin -- the building code requirement for heating is a performance-based requirement for a minimum of 68degF maintained 3' off the floor on a design heating day. (IBC 1203.1, IRC R303.10) Even in MN, a good low-ambient minisplit unit can meet this criterion without issue and without supplemental heat provided the building envelope is well-designed (i.e. properly air sealed and insulated, or in other words, a low-load envelope design) Aug 25, 2023 at 1:46
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It depends on where you are in New England. Darien CT and Lyme NH aren’t similar climates. Where I live the air temperature drops to -30°F and the ground water from my well is in the 40’s year round. Heat pumps can run in low ambient temperatures, they are not efficient that way. Unlike the western states the air in NE will condense requiring the machine to pump heat outside to defrost it frequently. Unfortunately the bulk of the heating cost is when it’s coldest, so the savings of using a heat pump when it’s mild outside while real, aren’t a large fraction of the annual heating cost. The added cost of a ground loop for heat pump is large, roughly the same as drilling 2 new water wells. If its undersized it will freeze underground and be utterly useless as a heat source for months, but the cost of a generously sized ground loop dwarfs decades of heating bills. The recommended system takes advantage of the low cost of adding heat pump functionality to an ac system. A good two stage thermostat will do a good job cutting off the heat pump and switching to the furnace. There are also fancy systems that use outdoor temperature to guide a changeover. Bottom line, if you’re in southern CT on the coast consider the heat pump seriously, elsewhere it’s likely to be an inadequate heating plant.

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I’ve installed a whole house Mitsubishi heat pump system. It’s whisper quite allowing normal conversation standing beside the dual fan outdoor unit. I whole house, a two level bungalow , keeps an even temperature throughout. It is 100% efficient to -23C then tapering off to zero efficiency at -40C when the heaters would kick in. We live in Souther Ontario when I’ve not seen -23C. In that most of Ontario runs off nuclear or water power the electricity is green energy. The local gas company provided a $6,500 rebate when it was installed. The Federal Central Mortgage and Housing authority provides up to 40K loans for 10 years at zero percent interest. It replaced a 22 year old hybrid system whose AC was working round the clock to keep up during the hot weather. A similar sized quality gas electric replacement system costs about 3K less than the heat pump system. The Mitsubishi system comes with a 10 year parts and labour warranty. I have used my supplier for over 20 years. My wife is extremely happy with the installation. I expect my annual energy costs to be lower and much lower in the future without carbon tax on gas usage and trending lower electrical energy costs in Ontario. Remember it a personal choice. Hope this helps Regards Frank London. Ontario, Canada.

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  • Forgot to mention an energy audit was done on my house showing it’s super efficient.
    – Frank
    Aug 11, 2023 at 21:04
  • This was useful until you got off track on the green energy/federal kickbacks/etc. tangents.
    – FreeMan
    Nov 17, 2023 at 21:04

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