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My house (Portland, OR, 2900 sq ft) has central gas heating and central AC. The house was built in 2017 and is well insulated, but every winter we face an annoying problem: downstairs and upstairs temperatures are controlled by the same thermostat, so if we heat things up enough to make the downstairs comfortable, the upstairs is too hot. The downstairs area where this is most acute is ~700 sq ft.

The house came with a gas fireplace in the downstairs living room (which is open to the kitchen as well), but it stopped working this year, and I'd like to move towards less reliance on gas anyway. I'm considering two options for providing supplemental heat to the downstairs:

  1. An electric fireplace (taking the place of the current gas one)
  2. A heat pump (as an augmentation to the existing central heating & cooling systems, since the house is ~2900 sq ft, and I don't really want to install enough heat pump capacity to cover the whole thing right now)

I've been looking at an electric fireplace which is ~$1500 and can output either 4800 (at 120V) or 10000 (at 240V) BTU. I'd probably hire someone for installation and removal of the old gas unit, at unknown cost. A heat pump of similar or greater capacity seems like it would likely be more. As a reference point, when I had one installed in an previous house in 2016, the equipment cost was about $2700 (for a Daikin FTXS12LVJU, rated for 14400 BTU of heating capacity @ 47 degrees F) plus another $1700 for installation. (The installation of this unit might be easier, since it is on the ground floor instead of the 2nd floor.)

From this post, it sounds like the most efficient electric fireplaces have a COP (coefficient of performance) of just over 1.0, whereas the Daikin model I referenced above has a COP of >4.0 for heating.

From a cost and efficiency perspective, does it make sense to consider a heat pump for this purpose?

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  • Running cost will very quickly favor spending more on a heat pump, rather than a toaster fireplace. Resistance heat is expensive to run. On the other hand, zoning your gas heat and/or running the fan all the time to even out temperature fluctuations, rather than only when heat is called for might solve your actual issue without either electric heat option.
    – Ecnerwal
    Feb 27, 2023 at 16:17

3 Answers 3

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First: all electric resistance heat will have a COP of 1.0. It's the nature of using electricity to directly make heat.

Second: given everything you've laid out, adding a heat pump to the basement sounds like a solid solution. It will probably not pay back the extra cost compared to an electric resistance heater all that quickly, given our low electric rates here, but the comfort levels will be higher, you won't second-guess running it, and you'll gain AC and dehumidification capacity. Go with whichever brand your well-reviewed installer recommends, as there are several great choices and you want them to work with something they are familiar with.

Also note that you'll want to adjust the ducting so that you aren't including the newly heat-pumped space in with the rest of your house's conditioned space.

And be realistic about your expectations. It's quite likely upstairs will still be warmer unless you really heat the basement an excessive amount.

Lastly: get the heating load for the basement properly calculated. My gut sense here is that you're looking at a little bit too big of a heat pump. The mini split units are great at throttling down, but they are even more efficient if they're sized correctly in the first place. They are so quiet that it's OK for them to run a lot to keep the space comfortable.

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Your heat pump plan is solid, but to some degree, this is a bit of an XY problem. Your existing central system is performing poorly, but instead of asking how to make it work better, you're reaching for supplemental equipment. It's likely that your existing equipment has all the heating capacity the house needs; the problem is one of air distribution.

I suggest you look for an air return from the lower level, near the floor. You might not find any. Adding air return capacity from that lower level will help in both seasons: in the winter it'll draw unpleasantly cold air from the lower level into the furnace. In the summer it'll draw pleasantly cooler air from the lower level and spread it through the house. In both seasons this will help to mix the air, working against the natural buoyancy that causes warm air to rise and cool air to sink.

If you set the thermostat to run the fan periodically that'll also help.

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  • I do have an air return vent on the lower level, in the room that I'm hoping to have better heating in the winter, but its' situated up high on the wall, rather than near the floor (which I gather is more typical). I will try running the fan though, since that's easy to try!
    – grumbler
    Mar 1, 2023 at 5:38
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Naturally the upstairs will be hotter than downstairs.

Hot air rises.

Limit or stop hot airflow from downstairs to upstairs, by closing the doors ect. The more you insulate the less hot air will be lost.

Install ZONE controller that will individually control upstairs and downstairs air flow.

For adding/increasing heat in specific area, heat pump is great solution and cost effective since it uses the thermodynamic laws to operate.

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