Fuel-energy conversions are planning approximations. Seasonal COP depends heavily on climate, heat-pump model, supply-water or air temperatures, building load and backup-heat operation. This tool estimates space-heating electricity only and does not automatically include domestic hot water or cooling changes.
Why seasonal COP matters
A heat pump can move several units of heat for each unit of electricity, but real seasonal efficiency depends on climate, equipment selection and the temperature your heating system must deliver. Use a conservative COP unless you have a modeled value for your home.
Finish the solar sizing workflow
Add the estimated heat-pump electricity to your existing household load, then use the Solar Panel Calculator or Home Solar Calculator. If roof area is a constraint, compare the result with the Roof Solar Calculator.