dpb wrote:

Pete C. wrote:
"Not@home" wrote:
...

My understanding is that heat pumps are more efficient, but need a
supplementary source of heat in areas where the winters are quite cold.

Air source heat pumps need supplemental (usually electric resistive)
heat in cold areas. Geothermal / ground source heat pumps don't since
their coils are below frost lines and soil temps are stable.

I'd revise that slightly as geothermal / ground source heat pumps _may_
not if sufficient heat source/sink capacity is available since
their coils are below frost lines and soil temps are relatively stable.

I'd revise that to "a geothermal heat pump with a correctly sized ground
loop" since in stable 55 or so degree soil a properly sized loop will
always be able to extract sufficient heat.