A heat pump's cooling rating gets most of the attention on a quote, but in a lot of the country its heating rating decides what the customer actually pays each year. HSPF2 is that heating rating. It's a seasonal number, so it's good for comparing models, and it needs a second look in cold climates.
HSPF2 in plain English
HSPF2 tells you how many BTUs of heat a heat pump delivers for each watt-hour of electricity it uses, averaged over a heating season. ENERGY STAR's specification spells it out: the total space heating required in Region IV during the heating season, in BTU, divided by the total electrical energy consumed by the heat pump system in the same season, in watt-hours1.
Two details in that definition matter:
- Region IV. The federal standard is based on Region IV heating hours2. Appendix M1 lets manufacturers optionally publish HSPF2 for other regions, but the required rating is Region IV3.
- "Heat pump system." The electricity counted is the heat pump system's over the whole modeled season, cold hours included, not just its best-case steady run.
How is HSPF2 different from HSPF?
DOE moved from HSPF to HSPF2 for heat pumps manufactured on or after January 1, 20232. The new Appendix M1 test changes several heating assumptions, summarized by New York State's Clean Heat program4:
| HSPF (Appendix M) | HSPF2 (Appendix M1) | |
|---|---|---|
| External static pressure, ducted | 0.1 to 0.2 in. w.c. | 0.5 in. w.c. |
| Heating test temperatures | 47°F and 17°F | 47°F, 17°F and 5°F |
| Where the heating load starts | 65°F outdoor | 55°F outdoor |
| Building load line slope | 0.77 | 1.15 non-variable speed, 1.07 variable speed |
| Typical number for the same unit | Higher | Lower |
Source: NYS Clean Heat, Efficiency Ratings Explained: DOE Appendix M1
The steeper load line means the test assumes the house needs more heat as it gets colder, which is closer to reality and puts more weight on cold-weather performance. NYS Clean Heat notes there's no single conversion between the two ratings, because each heat pump responds differently to the new test4.
What are the HSPF2 minimums?
Federal minimums under 10 CFR 430.32(c)(5), for heat pumps manufactured on or after January 1, 2023, apply nationwide (heat pumps have no regional HSPF2 levels)2:
| Product class | Minimum SEER2 | Minimum HSPF2 |
|---|---|---|
| Split-system heat pump | 14.3 | 7.5 |
| Single-package heat pump | 13.4 | 6.7 |
| Small-duct, high-velocity system | 12 | 6.1 |
| Space-constrained heat pump | 11.9 | 6.3 |
What is a good HSPF2 rating?
ENERGY STAR's Version 6.2 specification (revised March 2025) sets the next tier up, and adds a Cold Climate designation for heat pumps proven at low temperatures1:
The Cold Climate designation also requires 5°F heating capacity of at least 70% of the 47°F capacity, both measured under Appendix M11. Gas/electric packaged heat pumps aren't eligible for it.
HSPF2 vs COP
Seasonal average COP
COP (coefficient of performance) is heat delivered divided by electricity used, in the same units, at one set of conditions. HSPF2 is in BTU per watt-hour over a season. Since one watt-hour is about 3.412 BTU (EIA lists 3,412 Btu per kWh)5, dividing by 3.412 turns HSPF2 into a seasonal average COP.
| HSPF2 | Seasonal average COP |
|---|---|
| 7.5 (federal split minimum) | about 2.2 |
| 8.1 (ENERGY STAR Cold Climate, ducted) | about 2.4 |
| 9.0 | about 2.6 |
That's a seasonal average. COP at 5°F is a single cold-weather point and is usually much lower, which is why ENERGY STAR checks it separately.
How much does higher HSPF2 save?
Worked example (example inputs)
A house needs 30 million BTU of heat a season from the heat pump, and electricity costs $0.17 per kWh. Both are examples; real loads come from a Manual J and local rates.
| HSPF2 | Seasonal kWh (30,000,000 ÷ HSPF2 ÷ 1,000) | Seasonal cost |
|---|---|---|
| 7.5 | 4,000 | $680 |
| 9.0 | about 3,333 | about $567 |
| Difference | about 667 kWh | about $113 a year |
Treat it as an estimate. The rating uses Region IV weather; a colder or milder location will see different results.
Free calculatorBTU calculator (room and home sizing)Quick cooling load estimate by area, climate, sun and occupants. Not a Manual J.How HSPF2 shows up in TradesWork
When a tech recommends a heat pump in TradesWork, the options go out as a good-better-best proposal with rebates shown as an after-rebate price and an estimated yearly energy savings figure labelled as an estimate. For more on the cooling side of the same rating sheet, see SEER2.
Footnotes
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ENERGY STAR Program Requirements for Central Air Conditioners and Heat Pumps, Version 6.2, Rev. March 2025, definitions and Tables 2 and 3. https://www.energystar.gov/sites/default/files/2025-04/ENERGY%20STAR%20Version%206.2%20Heat%20Pump%20Specification%20Rev.%20March%202025.pdf ↩ ↩2 ↩3
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10 CFR 430.32(c), Energy conservation standards for central air conditioners and heat pumps, introductory text and paragraph (c)(5). https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-C/section-430.32 ↩ ↩2 ↩3
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10 CFR Part 430, Subpart B, Appendix M1, sections 5.1 and 5.2. https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-B/appendix-Appendix%20M1%20to%20Subpart%20B%20of%20Part%20430 ↩
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NYS Clean Heat (New York State), "Efficiency Ratings Explained: DOE Appendix M1," fact sheet CHC-CON-ashpM1-fs-1-v2, January 2024. https://cleanheatconnect.ny.gov/assets/pdf/CHC-CON-ashpM1-fs-1-v2.pdf ↩ ↩2
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U.S. Energy Information Administration, "British thermal units (Btu)," Energy Explained. https://www.eia.gov/energyexplained/units-and-calculators/british-thermal-units.php ↩
