Yeah the defrost cycle limits the heat pumps heating ability, but AC units have a similar limit wrt how much they are able to lower the temperature of the air.

Yeah the defrost cycle limits the heat pumps heating ability, but AC units have a similar limit wrt how much they are able to lower the temperature of the air. AFIAK they can do about 20 F. At this point you need to do some math and add additional units and run them 24/7 nullifying this benefit. Geothermal heat pumps and good insulation solve both.