HSPF (Heating Seasonal Performance Factor) rates how efficiently a heat pump heats a home across an entire winter. It is the heating-season twin of SEER, which rates cooling. A higher HSPF means more heat delivered for each unit of electricity, so it points straight at your winter electric bill.
Like the cooling ratings, HSPF got a stricter test in 2023 and a new name: HSPF2. The updated test runs equipment against more realistic ductwork pressure, so the numbers came out lower even though the hardware did not change. An older heat pump rated HSPF 8.8 maps to roughly HSPF2 7.5 on the same unit. Only compare HSPF2 to HSPF2.
The 2026 federal minimum is HSPF2 7.5 for split-system heat pumps (separate indoor and outdoor units) and 6.7 for packaged systems (everything in one cabinet). Most utility rebates and the ENERGY STAR label require more than the federal floor, so a heat pump that barely meets the minimum usually will not earn rebate money.
For a buyer, HSPF answers a different question than SEER. A two-in-one heat pump cools in summer and heats in winter, so you are buying two efficiency ratings at once: SEER2 for cooling and HSPF2 for heating. In a cold climate, weigh HSPF2 — and the cold-weather COP — more heavily, because that is the season that drives your bills.