Short answer: SEER2 measures cooling efficiency over a season, HSPF2 measures heat pump heating efficiency over a season, and COP measures efficiency at a single moment (heat out ÷ electricity in). Higher is better for all three. Since January 1, 2023, new split-system heat pumps must meet at least SEER2 14.3 and HSPF2 7.5 nationwide (DOE).
The ratings explained
| Rating | Measures | Applies to | Good to know |
|---|---|---|---|
| SEER2 | Seasonal cooling output ÷ electricity used | Central AC and heat pumps | New 2023 test method; not directly comparable with old SEER |
| EER2 | Cooling efficiency at a hot, fixed condition | AC and heat pumps | Matters most in very hot climates (Southwest standards use it) |
| HSPF2 | Seasonal heating output ÷ electricity used | Heat pumps | 8.5-10 is high efficiency; above 10 excellent |
| COP | Heat delivered ÷ electricity used at one temperature | Heat pumps, heat pump water heaters | COP 3 = three units of heat per unit of electricity |
| AFUE | Share of fuel turned into heat | Gas, oil and propane furnaces and boilers | Shown as a percentage, like 96% |
HSPF2 benchmarks from EnergySage.
Federal minimums (from January 1, 2023)
| Equipment | Minimum |
|---|---|
| Split-system heat pump | SEER2 14.3, HSPF2 7.5 (nationwide) |
| Single-package heat pump | SEER2 13.4, HSPF2 6.7 |
| Split-system AC, North | SEER2 13.4 |
| Split-system AC under 45,000 Btu/h, Southeast and Southwest | SEER2 14.3 (Southwest also has EER2 requirements) |
Source: DOE 2023 standards FAQ.
Why the “2”?
In 2023 the DOE changed the test procedure to better reflect real installations, for example by assuming more resistance from ductwork. The new ratings (SEER2, EER2, HSPF2) come out lower than the old ones for the same equipment, so don’t compare an old SEER number with a new SEER2 number. Compare SEER2 with SEER2.
What these numbers mean for your bill
Efficiency ratings tell you relative running cost. Going from a cooling rating of 14 to 18 means using roughly 22% less electricity for the same cooling (14 ÷ 18 = 0.78). Whether that’s worth the higher price depends on how much you run the system and your electricity rate. In a mild climate, paying a lot extra for top ratings rarely pays back; in Phoenix or Houston it can.
For cold climates, look deeper
- Capacity at 5°F (how much heat it still makes when it’s very cold).
- COP at 5°F (how efficiently it makes that heat).
- Minimum operating temperature.
Two units with the same HSPF2 can perform very differently in deep cold. See heat pumps in cold climates.
How to compare quotes
- Ask for the AHRI certificate number for the exact indoor and outdoor combination; ratings apply to matched systems.
- Compare SEER2, HSPF2 and capacity at 5°F side by side.
- Check whether rebates require minimum ratings or cold-climate certification. See rebates still available.
FAQ
Is a higher SEER2 always better? More efficient, yes; better value, only if you use it enough to recover the extra cost.
Can installation ruin a good rating? Yes. Leaky ducts, wrong refrigerant charge or poor airflow can waste much of the rated efficiency.