Does a typical (not special low-temp type) air-air heat pump provide any usable heat output below 0 degrees F? In looking at specs for popular brands, the lowest temperature for which data is given seems to be 0 degrees F. However in the area where I live, winter temperatures can drop to -20 F or even -25 F for a few days at a time.
I am wondering if the heat pump will still provide output to complement the electric resistance coils at these temps? Will it at least keep operating at C.O.P. = 1 or 0.95 and deliver most of the electric power going into it as BTUs in the house? Or will it completely stop operating at extremely low temperatures and leave me with nothing but the capacity of the resistance coils to warm the house?
The reason I am asking is that I want to make sure the HVAC contractor puts in large enough electric coils, if the heat pump doesn't give me any heat at all under extremely low temperature conditions.