[thraway3837]

Can someone please speak about their experience with the cost of running a heat pump for the same amount of time as a gas furnace or AC?

I’m still confused about why a heat pump is so much more efficient, since the only change from a typical AC and compressor setup is the two-way valve that allows the system to reverse and a different refrigerant. Would it still not use the same power hungry compressors as before? I always thought the most expensive part of running an AC was the compressor.

In terms of Gas, does it actually run cheaper than the per-therm Gas costs?

[rainsford]

I don't have direct comparative cost experience, but the reason heat pumps are so efficient is that while they do indeed have to run a fairly energy intensive compressor, that compressor allows them to get heat energy for free from the outside. By using the compressor to make the outside refrigerant very cold, it absorbs heat from the outside air (for air source heat pumps) even if it's cold outside. That absorbed heat energy required expending energy to run the compressor, but it ends up allowing the system to absorb several times more heat energy from the outside air. This marginally cools down the outside air, but that gets heated back up again by the sun. Arguably making heat pumps solar powered.

[datatrashfire]

It's not that it's more energy efficient than AC per se, just that running it in reverse to move heat into your house is much more energy efficient than using electricity to generate heat compared to electric resistance heat.

Relative to gas, it's going to be competitive when the ambient outdoor temperature is > 40 degree Fahrenheit, but probably more expensive depending on utility rates where you live.

[thraway3837]

If I rephrase what you said to make sure I understand it correctly: Cooling costs would be the same as AC units and heating would be cheaper or same depending on the cost of Gas. Would that be correct?

[Schroedingersat]

Generally. Depends a bit on climate, choice of heat pump, and relative energy costs.

A ground loop can make cooling cheaper too, as can upgrading to newer more efficient compressors.

[thraway3837]

Thank you! Also sounds like heat pumps come with multi or infinite stages akin to a CVT to be able to run at any speed for the heating or cooling demands. Rather than legacy units that are only On or Off.

Down in the comments, sounds like MA has good incentives, but not seeing other states. CA is banning new gas installations, so I assume heat pumps are the only way for new developments

[Schroedingersat]

> Also sounds like heat pumps come with multi or infinite stages akin to a CVT to be able to run at any speed for the heating or cooling demands. Rather than legacy units that are only On or Off.

Yeah, kinda. They can convert the incoming power to dc then back to ac at a different frequency so they can run at any speed. This cuts the energy losses from start-stop.

Less related to heat: It also has a neat side effect that it's a very simple change to make them run directly on solar with no (separate) inverter (and with no AC->DC step). On top of being more efficient even with AC->DC->AC this means in hot climates the energy used for cooling is used more efficiently, and the inverter on the solar array doesn't need to be as big (if you're getting full noon sunlight you probably want the AC on).

[pxmpxm]

I don't believe there is a municipality anywhere in the US where heat pump heating will be cheaper than nat gas on run rate basis.

[datatrashfire]

I actually used https://www.ncei.noaa.gov/products/land-based-station/us-cli... for my city to develop a model for the cost of btus from either method throughout the year and the heat pumps cope at that hourly temperature, and it was slightly cheaper for heat pump for the entire year. But I also live in a marine influenced climate in the west with low electricity rates.

[pxmpxm]

Whereabouts did that actually work? I can't think of a west coast locale where electricity is actually cheap and you get anything remotely resembling a winter.

I can see places like coastal california where you're on AC virtually year around and maybe need a day or two of heat.

[seanmcdirmid]

> I can't think of a west coast locale where electricity is actually cheap and you get anything remotely resembling a winter.

Eastern Washington? 10 cents kWH in Spokane.

I don’t know if any coastal Californian locale that needs AC for more than one or two weeks a year. Even in LA you can get by without AC.

[datatrashfire]

Yes! It could be more expensive too, the real kicker is utility costs and how cold your climate gets.

[pxmpxm]

New York here, heating via heat pump is about 5x as expensive compared to natural gas. Paid around 100 bucks in gas for 1700sq ft place with 18foot ceilings, where as our power bills are north of 400-500 for 1400 sq ft heat pump set up.

We have a new Daikin inverter heat pump set up in the 1400sq ft place and are actually retrofitting a nat gas solution - when it was 20F it took a full 24 hours to get our place from 55F to 70F because the pump stops for 15mins at a time to defrost.

Greenwash aside, I would not recommend the heat pump solution anywhere north of Atlanta unless you're doing underground coil + nat gas backup.

Also heat pumps are evidently terrible at humidity control - even in the "dry" mode our place would shoot up to like 70%+ RH, ended up getting whole house dehumidifier to handle this.