HSPF2 (Heating Seasonal Performance Factor 2) is the federal metric for residential heat pump heating efficiency. It expresses BTU of heating output per watt-hour of electricity averaged over a simulated heating season for a specific climate region.
Higher = more efficient. The federal minimum for the southern region is currently HSPF2 7.5 for split systems. Most quality heat pumps for SC are HSPF2 8.5-10.
HSPF2 captures the full picture of heat pump heating: the highly efficient operation at mild temperatures (where a heat pump might deliver 3.5x the heat per watt) and the less efficient operation at colder temperatures (where it may drop to 2x). For Charleston, where heating season is mild and short, real-world performance closely matches the rated HSPF2.
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