Heat Pump Size Calculator

A heat pump loses output as it gets colder while the house needs more, so the two cross at a temperature called the balance point. Enter the design heating load and design temperature along with the unit's rated capacity at 47 F and 17 F, and optionally at 5 F, and this returns where those two lines meet, how much capacity survives at the design temperature, and how many kilowatts of backup heat the shortfall leaves. A second mode works backwards, giving the 47 F rating needed to hold a balance point you choose and showing how far that size overshoots the cooling load. The load itself should come from a Manual J calculation, and capacity between the rated points is taken as a straight line rather than from the manufacturer's own table.