Heat pump ratings explained: SEER2, EER2, HSPF2 and AHRI certificates

U.S. heat pumps carry three federal efficiency ratings: SEER2 for seasonal cooling, EER2 for cooling at a single hot condition, and HSPF2 for seasonal heating. Higher is more efficient for all three. The "2" means the rating comes from the federal test procedure in Appendix M1, which manufacturers have used since January 1, 2023. For split systems, the ratings belong to a specific combination of outdoor and indoor equipment, which is what an AHRI certificate documents.

The three ratings

Rating	What it measures	Units
SEER2	Total cooling over a typical cooling season divided by electricity used over that season	Btu per watt-hour
EER2	Cooling output divided by power input at one test condition	Btu per watt-hour
HSPF2	Total heating over a heating season divided by electricity used over that season	Btu per watt-hour

The federal definition of HSPF2 is "the total space heating required during the heating season, expressed in Btu, divided by the total electrical energy consumed by the heat pump system during the same season, expressed in watt-hours."^{[Source 1]} HSPF2 ratings are calculated for climate Region IV.^{[Source 1]} NRCan notes that Region IV represents climates similar to the U.S. Midwest, and that heat pumps in colder places will see different seasonal results.^{[Source 9]}

Since one kilowatt-hour is 3,412 Btu (so one watt-hour is 3.412 Btu),^{[Source 10]} dividing an HSPF2 by 3.412 gives a rough season-average COP (coefficient of performance). An HSPF2 of 7.5 works out to about 2.2.

The 2023 test procedure change

Before 2023, ratings were SEER, EER and HSPF, tested under Appendix M. DOE's 2017 final rule created Appendix M1 and the new "2" metrics, required for ratings starting January 1, 2023.^{[Source 2][Source 3]}

The main change was the external static pressure the test assumes, which is the resistance from ductwork the blower has to push against. The old test used 0.10 to 0.20 inches of water column depending on capacity. DOE adopted "a minimum external static pressure of 0.50 in. wc. for all capacities of conventional CAC/HP products," because stakeholder data showed it "would be more representative of field conditions."^{[Source 2]} More resistance means more fan power, so the same equipment rates lower under M1. DOE's rule says the new metrics "generally have different numerical values than the current metrics."^{[Source 2]}

DOE's equivalence examples: "a unit rated at 15 SEER would be a 14.3 SEER2," and "an 8.8 HSPF would equate to a 7.5 HSPF2."^{[Source 4]} Those are DOE's examples, not a fixed conversion for every product. Compare SEER2 with SEER2, not SEER2 with an old SEER number.

Appendix M1 itself has been updated since. As amended in January 2025, it references AHRI Standard 210/240-2024, with compliance required from July 7, 2025.^{[Source 1]}

Federal minimums

DOE's minimums for heat pumps manufactured on or after January 1, 2023 apply nationwide:^{[Source 3]}

Product	Minimum SEER2	Minimum HSPF2
Split-system heat pump	14.3	7.5
Single-package heat pump	13.4	6.7

Regional standards (Southeast and Southwest) apply to central air conditioners, not to heat pumps.^{[Source 3]}

ENERGY STAR sets higher levels. Its Version 6.2 specification requires, for split heat pumps, SEER2 of 15.2 or more, EER2 of 11.0 or more and HSPF2 of 7.8 or more, with separate cold-climate criteria.^{[Source 8]} See Heat pumps in cold weather.

What an AHRI certificate is

The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) runs a certification program. AHRI explains that "for split systems, AHRI certifies the performance of the system and not the individual units," and that each matched system gets "a unique Certified Reference Number."^{[Source 5]} Products in the program are tested "by independent laboratories under contract to AHRI," with "a representative, random sample" tested each year.^{[Source 5]}

This matters because the same outdoor unit can have different ratings depending on the indoor coil or air handler it is paired with. A quote that lists the outdoor unit's best possible SEER2 may not match the combination being installed.

How to verify one

AHRI's advice for homeowners: "The easiest way to verify that the system is properly matched is to ask your installer for an AHRI Reference Number," which "can be entered into the AHRI Directory of Certified Product Performance to obtain a Certificate."^{[Source 6]}

1. Get the AHRI Certified Reference Number from your installer, or the exact model numbers of every component.
2. Search the AHRI Directory by reference number or by model numbers.^{[Source 7]}
3. Check that the outdoor model, indoor model and any other listed component on the certificate exactly match the quote and the installed equipment, including suffixes.
4. Read the SEER2, EER2 and HSPF2 on the certificate.
5. Keep a copy. The AHRI Directory also has a "Verify a Certificate" function that checks a certificate you were given against the directory, using the reference number, certificate date and certificate number.^{[Source 7]}

See AHRI certificate and Heat pump buying checklist.