Should I replace my gas furnace with a heat pump? I live in the coastal PNW, in a pretty moderate climate.
Nerd alert: I've kept pretty good records of our natural gas consumption, which averages about 450 therms per year total. Approximately 160 of that goes to our hot water heater (calculated by looking at summertime gas usage when the furnace is off and extrapolating out for the whole year). So that means we consume 290 therms to heat our house, for about six months of the year. We pay 88 cents per therm (including delivery charges), which means we spend 0.88*290= $255/year to heat our home with natural gas. That seems cheap, to me.
Our current gas furnace is a 20 year old 80% AFUE single stage unit, which means approximately 20% of the natural gas we buy goes up the chimney instead of into heating the house. In effect, this means our home really only needs 80% of those 290 therms, or 232 therms, to stay warm if we were 100% efficient. Unfortunately, upgrading to a 95% AFUE furnace isn't really cost effective for us, because it would only reduce our heating gas use from 290 to 251 therms, for a savings of $34/year. Big whoop.
Electrical heating (baseboards) are 100% efficient. If my house really requires 232 therms to stay warm, and the internet suggest that one therm is worth 29.3 kWh, then we could theoretically stay warm by using another 6798 kWh of electricity. At 7.41 cents per kWh, that would cost us $504/year. That's more than we currently pay for gas, which doesn't surprise me because baseboards are widely thought to be more expensive than gas heat.
But heat pumps are more than 100% efficient, because they are relocating heat from outside to inside instead of generating it by resistance. Around here, heat pumps reportedly average between 200% and 300% efficiency, so that reduces the power cost from $504/year to somewhere between $252/year (worst case, 200% efficient) and $168/year (best case, 300% efficient). I think.
So at the very least, it looks like switching to a heat pump is unlikely to cost us MORE per year to heat the house, other than the installation cost. This is an urgent decision, because we're adding a central air conditioner to our house (for several thousand dollars) and it's approximately $400 in added cost to put in a heat pump instead of an AC unit, since the two are apparently nearly identical mechanical objects with the addition of a reversing valve so it can pump heat out of OR into your house, depending on the season.
Other considerations:
1. heat pumps don't blast you with hot air the way a gas furnace does. They run more often, more quietly, delivering lower volumes of warm air instead of a blast of hot air that makes my dog lay next to the register on cold days. Right now, I can get home and have my house fully warm in less than 10 minutes.
2. heat pumps (and AC) units don't last as long as gas furnaces. Maybe 15 years, instead of 25?
3. We have solar panels, but they don't really figure into this calculation because we're grid tied and still "pay" for all of the power we use, either by buying it from the utility company or by not selling it to the utility company.
4. The house already has ducting and venting and an active gas line, and it seems a little silly to not use those advantages.
5. The lowest cost up-front option is to just add the AC to our existing 20 year old gas furnace, but it will need replacing eventually and doing it now as part of an AC install is cheaper than doing it next year as a separate job.
6. There is a slight eco-smugness benefit to going full electric with a heat pump, to reduce my family's carbon consumption.
Do any of you have experience with heat pumps in similar climates? How do you like it? What do you think I should do?
