Efficiency of a heat pump in the heating mode, taking cycling into account; the amount of heating provided per unit of electricity purchased. The higher the HSPF number, the more efficient the heat pump.

The total heating output of a heat pump during its normal annual usage period for heating divided by the total electric power input in watt-hours during the same period.

The total heating output of a heat pump during its normal annual usage period for heating, in Btu, divided by the total electric energy input during the same period, in watt hours, as determined by DOE 10 CFR Part 430, Subpart B, Test Procedures, and based on Region 4. Heat pump heating is expressed in terms of HSPF. New equipment ranges from about 6.8 to 10.0 HSPF. Higher HSPF ratings indicate more efficient equipment.