What is EER? The AC efficiency rating, explained
EER is the efficiency number for a hot afternoon. SEER2 covers the whole season. Which one matters depends on where you live.
EER in plain terms
EER stands for Energy Efficiency Ratio. It divides the cooling an air conditioner delivers, in Btu per hour, by the electricity it draws, in watts. A higher number means more cooling for each watt.
It is measured at one fixed condition: a hot outdoor day with the system running steadily. That is a snapshot, not a season.
How is EER different from SEER2?
| EER | SEER2 | |
|---|---|---|
| What it measures | Efficiency at one hot-day condition | Efficiency averaged across a cooling season |
| Best for | Hot climates, peak load | Comparing yearly running cost |
| Typical use | Window units, room units, hot regions | Central systems and heat pumps |
SEER2 is the headline number on most central systems. EER is the one to look at when the afternoon heat is what hurts.
When does EER matter most?
If you live where summer afternoons stay very hot, the system spends many hours near that test condition. In that case EER tells you more about real behavior than a seasonal average does. In a mild climate, SEER2 will say more.
Room air conditioners are usually rated by a combined number now, but EER still shows up on spec sheets and comparisons.
What EER does not tell you
EER ignores how your house is built. Leaky ducts, thin attic insulation and an oversized unit can waste more energy than the gap between two ratings. It also does not account for humidity control or noise.
So do not chase the highest EER on the shelf. A well-sized unit with a decent rating beats an oversized one with a great rating. Ask a licensed contractor for a load calculation before you buy.
Where do you find the EER?
Check the EnergyGuide label on room units, or the spec sheet and the AHRI certificate for central systems. The model number lets you look it up on the manufacturer's site.
This article does not quote prices, rebates or tax credits. They change and vary by state and utility, so ask a local licensed contractor.
Frequently asked questions
What is a good EER rating?
Higher is better, since it means more cooling per watt. What counts as good depends on the type of unit and your climate, so compare units of the same kind.
Is EER or SEER2 more important?
SEER2 gives the better picture of yearly running cost for most central systems. EER matters more in very hot climates where the system runs hard at peak.
Does a higher EER guarantee lower bills?
No. It means the unit itself is efficient. Poor sizing, leaky ducts and weak insulation can cancel out the benefit.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- ENERGY STAR. Energy Savings at Home: Heating & Cooling
- US EPA. Section 608 of the Clean Air Act