EER
Energy efficiency ratio: cooling output divided by electrical input at one fixed operating condition, rather than across a season. It is useful for comparing equipment at a specific outdoor temperature, which is why it appears alongside SEER on North American data sheets.
Also called energy efficiency ratio, EER2
What is EER?
EER is cooling output divided by electrical input at one fixed operating condition. Unlike SEER it is a single-point figure, which makes it useful for comparing performance on a hot day.
EER: how it works
EER fixes the operating conditions and reports the ratio at that point, which is a high outdoor temperature. Because it does not average across a season, it says how the equipment behaves when it is working hardest, which is the number that matters in a climate where the design day dominates the cooling bill.
Where you meet the term
- On a North American data sheet, quoted alongside SEER2 rather than instead of it.
- In a hot climate specification, where performance at high outdoor temperature is what is being bought.
- In a commercial rating, where single-point figures at several conditions are published.
How to check it
- Note the condition the figure was taken at. An EER without its operating condition is not comparable with another EER. The data sheet states the outdoor temperature used. Owner check
- Use EER alongside SEER, not instead of it. Seasonal and single-point ratings answer different questions, and equipment can score well on one and less well on the other. Owner check
Figures you will see
| Condition | Figure | What it tells you |
|---|---|---|
| Units | BTU per watt-hour | Divide by 3.412 to express it as a dimensionless ratio, which gives the cooling COP |
| Nature of the figure | Single operating point | SEER averages across a season, EER does not |
EER: what it is not
- EER is not a worse version of SEER. It answers a different question, and both appear on a data sheet for that reason.
- An EER quoted without its test condition cannot be compared with another EER.
EER questions
What is the difference between EER and SEER?
EER is measured at one fixed condition, SEER averages across a representative cooling season. Equipment that modulates well can score highly on SEER while a system built for sustained heat scores well on EER.
Is EER the same as cooling COP?
They express the same thing in different units. Dividing EER by 3.412 converts BTU per watt-hour into a dimensionless ratio, which is the cooling COP at that condition.
What is EER2?
The single-point rating updated to the 2023 United States test conditions, including the higher external static pressure. Like SEER2, it reads lower than the figure it replaced.
Where this definition comes from
Written from standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- AHRI Directory of Certified Product PerformanceCertified SEER2, EER2, and HSPF2 ratings for matched North American equipment combinations.