We went to Costco today to pick up a few things, and we mostly stuck to our shopping list. But when I saw that dental floss was on sale, I couldn’t resist and bought a card (six containers).

It’s just as well that I did control my bargain hunting instincts. When I got home, I discovered that we already had 40 containers of floss. Perhaps I’ll remember that we have enough next time we go to Costco.

I took my power question from last night to r/hvacadvice and got advice. One person used physics and math to convert my 150 therm consumption to 4175 kWh of heat, which would require about 1400 kWh of electricity over the season given the heat pump’s efficiency. Another person (who’s an “Approved Technician”) pointed out that I should make sure that the ductwork can handle the airflow from a 4-ton system (instead of the existing 3-ton), so I’ve asked the sales guy about that.

Saving money is hard work.

We got our first heat pump estimate today; the company is suggesting a 4-ton Daikin Fit system, which uses an inverter to provide variable speed airflow and reduce the temperature variation. Its SEER (cooling efficiency) is 18 and its HSPF (heating efficiency) is 10.

I also was able to download data for the past year from Ecobee (our thermostat) and found that the burner in the furnace was on for 275 hours and the compressor in the air conditioning was running for 127 hours during 2022.

I hoped to use this data to figure out how much power the heat pump would draw during the year, but I’m confused. The heat pump would not be cycling the way our existing system does – but it also wouldn’t be running full-bore when it’s operating. If I use the calculators at LearnMetrics, I get usage of 4.8 kWh per hour during heating season and 2.67 kWh per hour during cooling season – assuming 5 months of heating and 5 of cooling, that totals nearly 9,000 kWh for the year, which seems insanely high, given that the biggest solar system that’s been proposed to us only generates 10,000 kWh during the year.

I must be missing something.