HSPF2 (Heating Seasonal Performance Factor 2) is the efficiency rating for heat pump heating, required on all new heat pumps starting January 1, 2023. If you’re shopping for a heat pump or seeing these numbers on a spec sheet, here’s what they mean.
What the number means
HSPF2 measures how much heat a heat pump delivers per unit of electricity consumed over a heating season, measured in BTUs per watt-hour. A higher number means more heating output per dollar of electricity.
An HSPF2 of 8.5 means the heat pump delivers 8.5 BTUs of heat for every watt-hour of electricity used. For comparison, a simple electric resistance heater delivers about 3.4 BTUs per watt-hour (essentially 100% efficiency, but not extracting ambient heat like a heat pump).
This is why heat pumps cost less to operate than electric resistance heat: even at minimum HSPF2, they move more heat than they consume in electricity.
HSPF vs. HSPF2: how to compare
HSPF2 uses a more realistic test pressure than the old HSPF test, resulting in lower numbers for the same equipment. An 8 HSPF unit roughly equals 6.8 HSPF2. The approximate conversion is to multiply HSPF by 0.85, though it varies by unit.
When comparing an older unit you own (HSPF) to a new unit (HSPF2), the new unit may have similar actual performance even if the number looks lower.
2023 minimum requirements
The DOE minimum for all new heat pumps effective January 1, 2023 is 7.5 HSPF2. This applies nationwide regardless of region (unlike SEER2, which has regional minimums).
The actual test method behind both the old and new numbers is AHRI Standard 210/240, administered under the DOE’s test procedure (10 CFR Appendix M1 for the current HSPF2/SEER2 version) — the “2023 minimum” isn’t a separate rule so much as the same certification body’s output under a harder test.
What’s a good HSPF2 rating?
| HSPF2 rating | Tier | Notes |
|---|---|---|
| 7.5 | Minimum standard | Meets the 2023 requirement, nothing more |
| 9–10 | Mid-tier efficiency | Good balance of cost and performance |
| 11–12 | High efficiency | Variable-speed equipment |
| 13+ | Cold-climate heat pumps | Optimized for low-temperature operation |
Unlike SEER2, HSPF2 has one nationwide minimum rather than regional tiers — a cold-climate home benefits from chasing a high HSPF2 number specifically, since that’s the number that predicts how the system performs on the coldest days it’ll actually run, not just the average.
In colder climates, HSPF2 matters more than SEER2, since the heat pump runs for heating most of the year. A high HSPF2 cold-climate heat pump can maintain meaningful efficiency even below 0°F.
The relationship to auxiliary heat
HSPF2 ratings are measured at standard test conditions — but real heating efficiency drops at low outdoor temperatures. Heat pumps are most efficient in mild weather (35–50°F) and least efficient in extreme cold, where auxiliary electric resistance heat may take over.
A thermostat configured to minimize auxiliary heat use will realize more of the heat pump’s HSPF2 efficiency. See What Is Aux Heat? and Best Thermostat for a Heat Pump for thermostat settings that optimize heat pump heating efficiency.
HSPF2 and cold-climate heat pumps
Standard heat pumps begin losing efficiency (and output) around 25–35°F. Cold-climate heat pumps (like the Mitsubishi Hyper Heat, Bosch IDS 2.0, and Daikin Aurora) maintain high efficiency down to -13°F or colder. These units have higher HSPF2 ratings specifically because they’re tested across a wider temperature range.
If you’re in a climate that regularly sees temperatures below 20°F, HSPF2 at low ambient conditions (sometimes reported separately as HSPF2 at 5°F) is a more relevant spec than the standard HSPF2 number.
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FAQ
Is HSPF2 the same as COP? No. COP (Coefficient of Performance) measures efficiency at a specific temperature point. HSPF2 is a seasonal average across a range of temperatures and conditions. HSPF2 is more useful for comparing operating costs.
Does HSPF2 matter if I have a dual-fuel system? Less so. In a dual-fuel system (heat pump + gas furnace), the gas furnace takes over in cold weather anyway. The heat pump’s HSPF2 still matters for the milder portion of the heating season when it runs.
What HSPF2 do I need to qualify for tax credits? For federal Inflation Reduction Act (IRA) 25C tax credits, heat pumps must meet efficiency requirements specified in the current program year — check EnergyStar.gov for current thresholds, as they’re updated periodically.
Is a high HSPF2 heat pump worth the extra cost? In cold climates with high electricity rates and long heating seasons, yes — the payback period can be reasonable. In mild climates, the incremental savings may not justify the premium over a minimum-spec unit. Compare operating cost projections using actual heating degree days for your location.
