What do SEER2, EER2 and HSPF2 ratings mean?
The three efficiency numbers on every central air conditioner and heat pump: what each measures, the federal minimums, and how to compare quotes.
Published 7 min read
In short
SEER2 is cooling efficiency averaged over a season, EER2 is cooling efficiency at a hot 95 °F (35 °C) peak, and HSPF2 is a heat pump's heating efficiency over a season. Higher is better for all three.
Since January 1, 2023, equipment is rated under DOE's Appendix M1 test, which is what the "2" means. The numbers are not directly comparable with the older SEER, EER and HSPF.
Federal minimums depend on the product and region: for example SEER2 13.4 for a split air conditioner in the North, 14.3 in the Southeast and Southwest below 45,000 Btu/h, and SEER2 14.3 with HSPF2 7.5 for a split heat pump anywhere.
Every central air conditioner and heat pump sold in the United States carries a set of federal efficiency ratings. They decide whether a model may legally be installed where you live, and they are the fairest way to compare quotes. They are also easy to misread, because three of them look alike and all three changed their test in 2023.
What does each rating measure?
| Rating | Measures | In plain terms |
|---|---|---|
| SEER2 | Total heat removed over the cooling season ÷ total electricity used over the same season | How efficiently it cools across a typical summer |
| EER2 | Cooling capacity ÷ power input at peak load, 95 °F (35 °C) outdoors | How efficiently it cools on the hottest afternoons |
| HSPF2 | Heat delivered over the heating season ÷ electricity used, heat pumps only | How efficiently a heat pump heats across a typical winter |
All three are in Btu per watt-hour. Divide any of them by 3.412, the number of Btu in a watt-hour, and you get the plain ratio of heat moved to electricity used, the same thing as a coefficient of performance. A SEER2 of 15.2 is a seasonal average of about 4.45 units of cooling per unit of electricity.
The definitions above are DOE’s: SEER is “the ratio of the total heat removed from the conditioned space during the annual cooling season divided by the total electrical energy consumed”, and EER measures an air conditioner’s “peak load efficiency”, at 95 °F.
What does the “2” mean?
It marks the test. DOE revised its test procedure for central air conditioners and heat pumps, Appendix M1, and made it mandatory from January 1, 2023. Equipment certified since then carries SEER2, EER2 and HSPF2 ratings. DOE’s own note is that these “are similar to ratings using the original metrics”, but “are not directly comparable”. A model’s compliance is judged on its SEER2, HSPF2 or EER2.
In practice this means an old unit’s SEER printed on its nameplate cannot be compared number for number with a new unit’s SEER2. Compare new quotes with each other, in the new units.
The test keeps evolving. DOE adopted further amendments to Appendix M1 that became mandatory for product testing on July 7, 2025, and has defined two newer metrics, SCORE and SHORE, which also account for off-mode power. DOE says testing to SCORE and SHORE will not be required until an amended efficiency standard based on them takes effect.
What are the federal minimums?
DOE’s 2023 standards set national minimums by product, and regional ones for central air conditioners. The country is split by population-weighted heating degree days: states with 5,000 or more are the North. The South is divided into a hot-dry Southwest (Arizona, California, Nevada and New Mexico) and a hot-humid Southeast: Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, the District of Columbia, Puerto Rico and the U.S. territories.
National minimums, for equipment made from January 1, 2023:
| Product | SEER2 | HSPF2 |
|---|---|---|
| Split-system air conditioner | 13.4 | — |
| Split-system heat pump | 14.3 | 7.5 |
| Single-package air conditioner | 13.4 | — |
| Single-package heat pump | 13.4 | 6.7 |
| Small-duct, high-velocity system | 12 | 6.1 |
| Space-constrained air conditioner | 11.7 | — |
| Space-constrained heat pump | 11.9 | 6.3 |
Regional minimums for central air conditioners installed from January 1, 2023:
| Air conditioner type | North | Southeast | Southwest |
|---|---|---|---|
| Split, under 45,000 Btu/h | SEER2 13.4 | SEER2 14.3 | SEER2 14.3; EER2 11.7, or 9.8 if SEER2 is 15.2 or more |
| Split, 45,000 Btu/h and over | SEER2 13.4 | SEER2 13.8 | SEER2 13.8; EER2 11.2, or 9.8 if SEER2 is 15.2 or more |
| Single-package | SEER2 13.4 | SEER2 13.4 | SEER2 13.4; EER2 10.6 |
For scale, 45,000 Btu/h is 3.75 tons.
The rules differ in how they apply. In the North, the standard follows the date of manufacture: a unit made before 2023 to the older standard may still be installed. In the Southeast and Southwest, the regional standard for split air conditioners follows the date of installation, and DOE is blunt: “It is illegal for your air conditioner contractor to install a product that does not meet the regional standards in the Southeast and Southwest.”
How do ENERGY STAR levels compare?
ENERGY STAR’s Version 6.2 criteria sit above the federal floor. They still apply to heat pumps; the label for central air conditioners ended on February 1, 2026.
| Product | ENERGY STAR SEER2 | ENERGY STAR EER2 | ENERGY STAR HSPF2 |
|---|---|---|---|
| Split heat pump | 15.2 or more | 11.0 or more | 7.8 or more |
| Single-package heat pump | 15.2 or more | 10.0 or more | 7.2 or more |
| Cold-climate heat pump, ductless | 15.2 or more | — | 8.5 or more |
| Cold-climate heat pump, ducted or packaged | 15.2 or more | — | 8.1 or more |
| Split central air conditioner (until Feb. 1, 2026) | 15.2 or more | 12.0 or more | — |
Cold-climate heat pumps must also meet low-temperature performance tests at 5 °F (−15 °C), which a seasonal HSPF2 alone does not show.
Whose rating is it: the outdoor unit or the system?
A split system’s rating belongs to a combination of outdoor unit and indoor coil or air handler, tested and certified together. ENERGY STAR requires manufacturers to state that split systems, other than ductless ones, “must be matched with appropriate coil components” to meet its criteria.
This matters when only the outdoor unit is replaced. DOE’s guidance for the 2023 standards works through the cases:
| Situation | North, and all heat pumps | Southeast and Southwest air conditioners |
|---|---|---|
| New outdoor and indoor units, certified as a combination | No restriction | Allowed if the combination meets the regional standard |
| New outdoor unit with an existing, older indoor unit | Compliant for sale if the outdoor unit was certified as an outdoor unit with no match, under the new test | Allowed only if the outdoor unit is certified, with no match, to the regional standard |
| Combination never certified | Not compliant for sale | Not compliant for installation |
Ask the contractor for the certified ratings of the exact model numbers being installed together, not the brochure figure for the outdoor unit.
How do I use the ratings to compare quotes?
- Compare like with like. SEER2 with SEER2, for the same capacity and the same combination.
- Weigh SEER2 by your climate. Seasonal electricity use for cooling scales roughly with 1 ÷ SEER2 for the same cooling load, so a higher rating pays back faster where summers are long and electricity is expensive.
- Look at EER2 in hot, dry places. It shows how the system performs at the peak, on the hottest afternoons.
- For heat pumps in cold places, look past HSPF2. It is a seasonal figure for a reference climate. Capacity and COP at 5 °F (−15 °C) tell you more about the coldest weeks.
- Get the numbers in writing, for the certified combination, before you sign.
Questions
- What is a good SEER2 rating?
- It depends on your climate and electricity price. The federal minimum for a split air conditioner is 13.4 in the North and 14.3 in the Southeast and Southwest for units under 45,000 Btu/h. ENERGY STAR's criteria for split heat pumps start at SEER2 15.2. Higher ratings save more electricity in places with long, hot cooling seasons.
- Is SEER2 the same as SEER?
- No. SEER2 is measured under the revised DOE test procedure required since January 1, 2023. DOE says the new ratings are similar to the old ones but not directly comparable, so compare SEER2 only with SEER2.
- Why does EER2 matter if I already know SEER2?
- SEER2 is a seasonal average; EER2 describes efficiency at peak load, when it is 95 °F (35 °C) outside and the system is working hardest. DOE notes it matters most in hot-dry climates, and the Southwest has EER2 minimums as well as SEER2 minimums.
- Can I install a new outdoor unit with my old indoor coil?
- Ratings belong to certified combinations. DOE's guidance says that in the North, and for heat pumps, a replacement outdoor unit is compliant for sale if the manufacturer certified it as an outdoor unit with no match under the new test; in the Southeast and Southwest it must also be certified to the regional standard. Ask for the certified rating of the exact combination you are buying.
Sources
- U.S. DOE — 2023 Energy Conservation Standards for Residential Central Air Conditioners and Heat Pumps: FAQ (October 5, 2022)
- U.S. DOE — Consumer Central Air Conditioners and Heat Pumps
- ENERGY STAR — Central Air Conditioner and Heat Pump Specification, Version 6.2 (Rev. March 2025)
- ENERGY STAR — Central Air Conditioners Sunset
- U.S. EIA — British thermal units (Btu)