EER tells you how efficiently an air conditioner cools on a hot day. Where SEER2 averages a whole season, EER measures one hot test condition, which is why it matters most in places where the hottest afternoons drive the bill.
EER is cooling output in BTU per hour divided by the power drawn in watts, at 95°F outdoors. At EER 11, the ENERGY STAR minimum EER2 for split heat pumps, a 3-ton system draws about 3.3 kW; at EER 8 it draws 4.5 kW, about 81 cents an hour at 18 cents per kWh against 59.
EER chart: watts per ton and cost per hour
| EER | Watts per ton | 3-ton system draws | Cost per hour at 18 cents |
|---|---|---|---|
| 8 | 1,500 | 4.50 kW | $0.81 |
| 9 | 1,333 | 4.00 kW | $0.72 |
| 10 | 1,200 | 3.60 kW | $0.65 |
| 11 | 1,091 | 3.27 kW | $0.59 |
| 12 | 1,000 | 3.00 kW | $0.54 |
| 13 | 923 | 2.77 kW | $0.50 |
| 14 | 857 | 2.57 kW | $0.46 |
Watts per ton = 12,000 ÷ EER, because one ton is 12,000 BTU per hour. The cost per hour applies while the system runs at full output on a hot day.
Reading EER from a nameplate
EER is simple enough to read off a label yourself: divide the cooling output in BTU per hour by the watts the unit draws. Suppose a window unit lists 10,000 BTU per hour of cooling and 1,000 watts. Its EER is 10,000 ÷ 1,000 = 10.
A window unit's published CEER sits slightly below that running figure, because CEER also folds in the small amount of power the unit uses in standby. For a central system the same math runs per ton: at EER 10 a ton draws 1,200 watts, which is the 12,000 ÷ 10 in the chart above.
Good, average and excellent
- Below 10: typical of older or basic equipment. It works, but costs more on the hottest days.
- Around 11: the level ENERGY STAR requires for split heat pumps (at least 11.0 EER2).
- 12 and above: high efficiency at peak heat, worth paying for where long, hot afternoons dominate cooling.
These bands are a reading guide anchored on the ENERGY STAR threshold, not an official rating scale.
EER2 minimums you can check against
The federal single-point rating carries its own floors on top of the seasonal SEER2 rules. ENERGY STAR sets a minimum EER2 at the hot test point for the equipment it certifies, which gives you a concrete pass mark rather than a loose band.
| Equipment | ENERGY STAR EER2 minimum |
|---|---|
| Split heat pump | 11.0 |
| Single-package heat pump | 10.0 |
ENERGY STAR publishes these EER2 floors for the heat pumps it certifies, with the single-package figure set a little below the split one. On the regulatory side, split air conditioners must meet 13.4 SEER2 in the North and 14.3 in the South and Southwest, dropping to 13.8 at 45,000 BTU per hour and above in those two regions. The Southwest alone adds a minimum EER2 at the single hot test point, the same kind of rating this chart is built on.
EER, EER2 and SEER2
- EER is a single-point rating at 95°F outdoors.
- EER2 is the same idea under the federal test procedure used since 2023, which applies higher airflow resistance, so it reads lower than the old EER for the same equipment.
- SEER2 averages efficiency across a range of outdoor temperatures and loads, so it's usually higher than EER2 for the same unit.
A variable-speed system can have a very high SEER2 but a more modest EER2, because its advantage shows at part load, not at full output on the hottest day. At the ENERGY STAR floor a split heat pump pairs 15.2 SEER2 with only 11.0 EER2, so the seasonal number runs about 38% above the single-point one (15.2 ÷ 11.0 = 1.38). See SEER2 explained.
By type of air conditioner
- Central air and heat pumps: EER2 appears in the AHRI Directory for each certified combination of outdoor and indoor unit.
- Window units: rated by CEER, which also counts the power used in standby.
- Mini splits: rated by SEER2 and EER2 like central systems; their high SEER2 comes mostly from running at low speed.
- Portable units: rated by CEER against a seasonally adjusted capacity (SACC). Single-hose models pull warm air into the room, which lowers their effective efficiency; see single-hose vs. dual-hose portable ACs.
Frequently asked questions
What is a good EER rating?
About 11 or higher is a good target; that is the level ENERGY STAR requires for split heat pumps. Where summers are long and hot, 12 or above pays off.
How do I find my air conditioner's EER?
Look up the outdoor and indoor unit model numbers in the AHRI Directory, which lists certified EER2 and SEER2 for each combination. Window and portable units list CEER on their EnergyGuide label.
What's the difference between EER and SEER?
EER is efficiency at one hot condition, 95°F outdoors. SEER averages a whole cooling season, so it's usually higher.
Does EER matter more in hot climates?
Yes. When a system spends many hours at full output on hot afternoons, its efficiency at that condition, which is what EER measures, drives most of the bill.
Sources & References
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