Newer heat pump vs new space heaters in Seattle winter

Question

I see similar questions to this one, but mine is slightly different, so here goes:

I live in Seattle, where the winters are mild, with days in the 40s°F (4-10°C) and nights in the low 30s°F (around -1°C) at worst. I live in an 8-bedroom house with all bedrooms occupied (tenants). The house has no outer wall insulation at all, but windows are double-pane and we have checked for and fixed drafts. I have a newer heat pump tied to an electric furnace, also newer.

I prefer a house at 64°F (18°), but my tenants are all comfortable at mid-70s°F (24°C) and I have argued to no avail. My heating bill is way too high for me now. What I am left with is the choice between turning the house up to 74°F (23°C) or so, or keeping it at 68°F (20°C) and buying them new space heaters with adjustable thermostats (they all have older ones now with no thermostats). They already turn the heaters off when they are not home. I see lots of good science on this site, although most of it is over my head, but I can understand the basics. Should I heat the whole house or trust the space heaters?

Answer 1

There are at least two possible considerations I can see in your question. First, the implied consideration of efficiency/environmentalism/sustainability. I assume you want to minimize your power use for heating purposes to satisfy this consideration. Second, the stated consideration of your "preference". You don't say whether this is a comfort preference or some other sort.

In terms of comfort, a solution with multiple thermostats is presumably going to win out. This will let everyone in the building have their main living space at the temperature they prefer. This could be a heat pump (mini-split?) and a number of thermostat-controlled space heaters (electric resistive, presumably). Or it could be a multi-split heat pump.

In terms of efficiency/etc, air-sealing and insulation are going to factor heavily into the solution. Nothing you do in terms of changing the thermostat or introducing additional heating zones to the building is going to save as much power as reducing your heating losses to the outside environment. Your best move is probably to consult with a heating efficiency expert - likely have a blower-door test, air sealing, and perhaps insulation installed. In very cold climates, this can easily pay for itself in a small number of years. In a more moderate climate like yours, it may take a bit longer but it's still a pretty smart bet.

Once this is done, even if you resort to electric resistive space heaters (much less efficient than the heat pump) to bring extra heat to some parts of the house, you're at least keeping that heat where it's desired for longer and so it's not as inefficient. A multi-split heat pump set up would be even better but is certainly going to have a higher up-front cost.

Answer 2

Insulate the house. It's worth it.

You are better off to run the heat warm enough to make your tenants happy, then restrict the heat to your part of the house. If you are using conventional forced air heating, then putting adjustable grates in the tenants rooms will be sufficient.

The thermostat is in your part of the house. Set it for 64. Because your vents are partially blocked to get your part of the house to 64 will put your tenants at some higher temp.

If your tenants then say that their room is too cold, but you are comfortable, you block more of your vents, making the heating system work harder.

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Insulating the house.

This is moderately expensive no matter how you do it. If PU foam is legal where you are, you can drill holes in the siding, fill with foam, then cap the holes. Improperly mixed PU resulted in formaldehyde poisoning. This is NOT a DIY option.

You can blow cellulose or fiberglass insulation into the wall cavities from either inside or outside. This settles, and so needs to be redone. But having the bottom 7 feet of the wall insulated would be better than none.

If re-siding the house is in your future, you can apply a layer of breathable foam panels. (The foam is in effect needle punched to allow it to breath). 2 inches would give you about R8 to R14 depending on which foam. It's a good idea to build in a rain screen -- a very narrow space between the foam and the wall that allows either incoming rain, or outgoing condensation to drain out of the wall. Note that window and door trim has to be built up to match the new wall thickness.

Answer 3

The most obvious solution is to insulate your house. You will spend loads less money on heating by insulating the exterior walls, which will prevent heat from escaping into the outdoors. Right now I imagine your heating system is working very hard to maintain even a "cool" indoor temperature of 64, let alone temperatures in the 70s. Insulating will be an upfront expense, obviously, but in the long run it will save a lot of money on your heating bill (and it's better for the environment).