HSPF2
heating seasonal performance factor 2 · HSPF
HSPF2 (heating seasonal performance factor 2) is the federal rating of a heat pump's heating efficiency over a whole season, in Btu of heat per watt-hour of electricity, measured under DOE's Appendix M1 test procedure.
HSPF2 sums up a heating season in one number: the heat a heat pump delivers over a standardized season divided by the electricity it uses to do it. The higher the number, the less electricity per unit of heat.
The “2” marks the test procedure. Since January 1, 2023, manufacturers must rate and certify central air conditioners and heat pumps under Appendix M1 of the federal test rules, using the metrics SEER2, EER2 and HSPF2. Because the test conditions changed, an older HSPF value and an HSPF2 value cannot be compared directly.
For reference, ENERGY STAR Version 6.2 asks for HSPF2 of at least 7.8 for split heat pumps, and at least 8.5 (ductless) or 8.1 (ducted and packaged) for its Cold Climate designation. A seasonal rating does not show how a unit performs on the coldest days; for that, look at the coefficient of performance and capacity at 5 °F (−15 °C).
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