4 ms·
I had heat pumps added to my home this past summer, primarily to provide air conditioning. This article is a good overview of what I learned in the process. I'l
by peter_l_downs 3y ago
I had heat pumps added to my home this past summer, primarily to provide air conditioning. This article is a good overview of what I learned in the process. I'll add a few lessons:
- Get a few quotes and iterate on the plan. Save the contractor you'd most prefer to work with for last, because you'll have a much better idea of what you want by then, and your knowledge will save you money.
- There's a fun puzzle to retrofitting older homes (no existing ducts): where you place the lines, where you place the units, and where you place the heads are all variables to play around with. This is part of the reason for getting different quotes. Only the last two contractors I spoke with were able to come up with ways to keep all the external lines on the side of my house and away from the street. Only the very last contractor offered a ducted system for bedrooms, so I have head units downstairs but the upstairs is vented.
- No one will run a real Man J calculation, they all use proxy calculations. This should be fine but you almost certainly want to slightly undersize your system. If your system is always turning on and then turning off (because it is oversized and heating / cooling the room very quickly) you'll end up with humidity and mildew problems, you want it to be running "low and slow" while it's on.
- They work amazing for air conditioning. For heat, your existing boiler + radiators is often nicer and more cozy. It's also often cheaper — heat pumps are electrically efficient, but natural gas costs vary significantly by location and for me (~Philadelphia) heating with my boiler is a lot cheaper than doing it with the heat pumps.
- I live in an older home, so before I installed heat pumps I had to replace my ancient windows for modern ones that didn't constantly leak energy. I'm happy with the results but it adds a lot to the startup cost.
- amluto 3y agoEven Manual J (in my quite limited experience) can give wildly inflated results. For example, if a big window has a tree in front of it or a reasonably reflective or insulating window treatment (and you close it on a hot day!), then your Manual J software may estimate the heat load as if the sun were shining full blast through the glass all the time and give a huge number. I intentionally had a contractor install a unit that was undersized per Manual J in a room, and, as tested during a nearly-record-breaking heat wave, it kept up without coming close to its limits. Fortunately, a lot of modern systems have respectable turndown ratios (better than 5:1 is not that hard to find), so as long as you use controls that can operate the system all the way down to minimum power, oversizing is not that bad.
- Kirby64 3y agoModern inverter based heat pumps are perfectly fine to oversize. Since you can adjust the speed of the compressor, you just run the compressor slower if you want to 'undersize' it. There's little downside aside from cost to oversizing these days, and in many cases it may be necessary to oversize the cooling side to provide enough heating in the winter.
- christkv 3y agoWe are building a new house now and the heat pump will actually provide heating a cooling through panels installed in the ceiling and walls.
- sokoloff 3y agoPresumably not in a highly humid summer environment? Radiant cooling is limited to dew point, so works poorly in humid environments (or requires whole-house dehumidification to lower the dew point).
- christkv 3y agoNot Miami humid for sure. Temperate European environment. Lowest temperature in the water cycle is 18C or 64.4F and max temperature is 30C or 86f. House is passive so insulation is pretty good and there is an active ventilation system. Panels are pretty big and located in the ceilings and walls so should help aswell. https://sunthalpy.com/en/products/sunthalpanel/ https://sunthalpy.com/en/products/sunthalpanel/