> The place I've lived for 15 years had a heat pump and a (oil) boiler with radiators, and when it was below 40°F (~5°C) I had to switch to the radiators.
When was the heat pump manufactured? Mitsubishi, for one, publishes data were they have 100% heating capacity at -15C, which some models being 100% at -20C and -23C:
OEMs can optionally have publish data on "Lowest Cataloged Temperature" if it's below 5F/-15C.
Also: how (air) leaky is your house? how much insulation? For a lot of folks dealing with those two things would be more cost effective than anything.
As it stands, even if you are heating with "cheap" methane (née 'natural') gas, propane, or oil, you're throwing money out the window by letting the heat out in winter. (And the heat in / cold out in the summer.)
When was the heat pump manufactured? Mitsubishi, for one, publishes data were they have 100% heating capacity at -15C, which some models being 100% at -20C and -23C:
* https://www.mitsubishielectric.ca/en/hvac/home-owners/zuba
There's a website for cold climate air-source heat pumps (ccASHPs), that has performance data down to (at least) 5F/-15C:
* https://neep.org/heating-electrification/ccashp-specificatio...
* https://ashp.neep.org/#!/
OEMs can optionally have publish data on "Lowest Cataloged Temperature" if it's below 5F/-15C.
Also: how (air) leaky is your house? how much insulation? For a lot of folks dealing with those two things would be more cost effective than anything.
As it stands, even if you are heating with "cheap" methane (née 'natural') gas, propane, or oil, you're throwing money out the window by letting the heat out in winter. (And the heat in / cold out in the summer.)