Cooling and heating use different seasonal ratings
SEER2 describes seasonal cooling efficiency under a standardized test procedure. HSPF2 describes seasonal heating efficiency. Higher values indicate less electricity used for the standardized seasonal output, but the numbers are not interchangeable and do not predict a specific home's utility bill by themselves.
The “2” identifies updated U.S. test procedures that took effect in 2023. Do not directly compare an older SEER or HSPF value with a newer SEER2 or HSPF2 value as if the test conditions were identical.
What the seasonal labels omit
A seasonal rating compresses many test conditions into one value. It does not fully show how much heating capacity remains during a cold snap, the electricity used by backup resistance heat, the effect of defrost, duct losses, installation quality, or thermostat settings.
- Check rated heating capacity at 47°F, 17°F, and 5°F where available.
- Use coefficient of performance at low temperatures to compare operating efficiency.
- Review capacity maintenance and the approved indoor/outdoor match.
- Ask how controls stage the compressor and backup heat.
Efficiency is only one sizing input
The most efficient model on a rating sheet is not automatically the best selection. It still needs enough capacity at the design condition, acceptable airflow, a suitable operating range, and controls that match the application. Oversizing can also compromise humidity control and comfort.
A practical comparison workflow
First define the home's heating and cooling loads. Then shortlist matched systems with enough capacity at local design conditions. Compare low-temperature COP and capacity, then seasonal HSPF2 and SEER2. Finally evaluate sound, controls, service availability, warranty terms, and installed scope.