The measure of a heat pump’s heating performance is called coefficient of performance (COP). It’s the ratio of useful heat output divided by required energy input, where both the output and input are expressed in the same physical units.
By now, most of you have either installed inverter-driven variable speed heat pumps that can deliver their nominal rating output at temperatures well below 0° F without any backup heat source, or at least have become familiar with the technology.
As global energy planning moves away from fossil fuels and toward electricity, an increasing number of hydronic heating systems are being supplied by heat pumps.