What the rating measures
SEER stands for seasonal energy efficiency ratio. It is measured under a standard test that averages performance across a range of conditions, so different models can be compared on equal terms.
The rating has been revised over the years, and newer equipment is often labeled SEER2, which uses an updated test meant to better reflect how systems perform once installed. A SEER number and a SEER2 number are not directly comparable.
Related ratings
- EER, or EER2, measures cooling efficiency at a single hot condition rather than across a season
- HSPF, or HSPF2, rates a heat pump’s heating efficiency
- AFUE rates how much of a furnace’s fuel becomes heat in the house
What the number does not tell you
A rating describes the equipment in a test, not the system in the house. Correct sizing, a matched indoor and outdoor unit, the right refrigerant charge and ducts that do not leak all affect how efficiently a system really runs.
Minimum ratings vary by region and change over time, so it is worth asking what applies locally.
Choosing a rating
Higher-rated equipment usually costs more to buy and less to run. Whether that trade makes sense depends on the climate, how much the system runs, local electricity rates and how long you plan to stay in the house.