COP
Coefficient of performance compares heat delivered with electricity used at a particular condition. A seasonal average is more useful for annual cost than a mild-weather point rating.
SEER and SEER2
Seasonal Energy Efficiency Ratio is a cooling-season efficiency metric based on standardized testing. It helps compare equipment, but actual use still depends on load and installation.
System performance
Sizing, ducts, refrigerant charge, controls, airflow, backup heat, and climate can materially affect delivered efficiency. Use qualified design advice for a purchase.
Use the numbers
Apply this guide with one of WattMeasure’s free calculators. Results are planning estimates and should be verified for consequential decisions.
Last reviewed August 6, 2026