Glossary · Heating, cooling & ventilation
EER / EER2
Also called: energy efficiency ratio
Cooling efficiency measured at one hot test condition rather than averaged over a season; useful for judging performance on the hottest days.
What it means
Unlike SEER, which averages over a season, EER measures steady-state efficiency at a single hot outdoor condition, so it's a better guide to electricity use on peak days. EER2 is the version used since 2023. For ground-source heat pumps, EER is the standard cooling rating.
Why it matters in an audit
In hot-dry regions such as the US Southwest, federal rules set a minimum EER2 as well as SEER2, and a high EER helps limit electricity use during heat waves.
Typical numbers
Reference values with their sources. Your auditor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| US Southwest minimum, split air conditioners (2023) | EER2 11.7 (below 45,000 BTU/h) or 11.2 (45,000 and above) when SEER2 is under 15.2; 9.8 when SEER2 is 15.2 or more | www1.eere.energy.gov ↗ |
| US Southwest minimum, single-package air conditioners | EER2 10.6 | www1.eere.energy.gov ↗ |
| ENERGY STAR heat pumps (spec 6.2) | Split EER2 ≥ 11.0; single-package ≥ 10.0 | energystar.gov ↗ |