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Chagrinnish t1_j1avx5z wrote

Reply to comment by Bunslow in Why do we use phase change refrigerants? by samskiter

Here's a Goodman brand heat pump spec sheet (see p21) with COP numbers vs. ambient air temperature. They're giving a COP of 1.2 to 1.5 (120% to 150%) at -10F. It's going to be pretty cold before you'll want to use any resistive heat. The more important factor is that it can't put out as much heat (MBh in the chart) so it might not keep up.

Edit: Looking at price of Propane, Natural Gas, and electricity (in Iowa prices) you need a COP of 1.9 or 2.2, respectively, for the heat pump to be more cost effective. So that translates to the heat pump being more cost effiective around 5F and above vs propane or 15F vs natural gas. Unfortunately it's -6F right now :)

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softdetail t1_j1bcp21 wrote

True but it's only that cold for a small portion of the season, so on average, you are still saving money

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Bunslow t1_j1bfexu wrote

well i dont exactly have any way to burn fuel around here, so all i got are resistors or heat pumps. lol. im in IL, so not that far away. 0F and falling to the same -9F low. apparently we have the same low temperature from st louis to winnipeg, it's a massive blast of fairly homogenous air

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