Heat pumps still pumping at -16

Overnight lows hit minus 17 degrees in Montpelier and weren’t much warmer come morning. The cold-climate heat pumps we installed upstairs and downstairs in our 1880’s cape were put to the test last night. Guess what – they’re still working!

What to do on days like today was one of the biggest questions we had when making the leap to heat pumps. We do have a wood stove that we get going on cold evenings and weekends, but since we both work full-time out of the house, we can’t tend the stove on subzero weekdays.

So, while our goal is to eliminate our use of fossil fuels in the home, we kept the oil heat furnace as back-up. So far, we haven’t had to use it.

Since we weatherized a couple years ago, the house holds heat much better. We’re also comfortable keeping indoor temps closer to 60 degrees than 70, so it’s not tropical. Our downstairs unit heats the kitchen and dining space comfortably, but the living room next door is typically 5-10 degrees cooler, since the spaces are connected just by a couple doorways. The upstairs unit in the hallway, along with heat rising from the lower level, keeps the upstairs bedrooms comfortable when the doors to the hallway are kept open.

Downstairs heat pump.

Our electric bill has gone up about $100 per month during these cold months where the heat pumps are working hard. This is offset by excess solar production from our photo-voltaic system that we sized to maximize our rooftop solar production. Pre-heat pump installation, we generated a $700 credit of electric generation. With heat pumps, we still expect a net positive electric production to use for the calendar year.

Oh yeah, and compared to the >$2,500 we spent on heating oil last winter, I’d say $100 more on electric is a bargain!

In full disclosure, the heat pumps do seem to be working a bit harder than usual on these cold days. We reset the downstairs unit once and it takes a while – about 10-15 minutes – when you turn them off and back on to get them heating again. But snapping these pics this morning these were blowing hot air. How they pull heat from such cold outside air is physics I’ve had explained multiple times…all I know is they’re working.

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