After using a single stage heat pump for a year I have some results to share regarding the cost of cooling and reduction in natural gas.
For heating, the time periods I’m reviewing are September 2020 through May 2021 which is before we got the heat pump and September 2021 through May 2022 which is using a heat pump. What I found was a 46% reduction in natural gas usage due to the heat pump, now down to 292 therms (about a quarter of a comparable home).
Obviously this is an imperfect comparison due to weather differences, but I think it’s safe to say that the heat pump made a significant difference in natural gas use. I see two major advantages to reducing natural gas use – obviously there’s the emissions difference of 11.7lbs of CO2 per therm, but also isolation from the rapid increase in natural gas prices.
I have the Emporia Vue Energy Meter watching the heat pump circuit to learn about costs. What I’ve learned about cooling is that we have 2 significant cooling months in Western Washington – July and August. Running a 4 ton heat pump to cool our house costs about $38/month at PSE Tier 2 rates those months. Other months are pretty trivial, for example September heat pump operation was less than $8, but also likely had some heating cost involved as in the past we used 9 therms of natural gas in September.
So is a single stage heat pump a good idea in Western Washington? I think it depends on your goals – if you want to reduce natural gas and get affordable cooling it works great. If you want to eliminate natural gas use you’ll need a variable speed heat pump system.