Energy Efficiency Ratio (EER)
Cooling capacity in BTU/h per watt of power — a common AC rating.
Formula
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Example
12,000 BTU/h at 1000 W: EER = 12
How it works
The Energy Efficiency Ratio (EER) tells you how much cooling an air conditioner provides for each watt of electrical power it uses. It works by comparing output to input: the cooling capacity is measured in BTU per hour, and the electrical demand is measured in watts, so dividing the two gives a direct efficiency score. A higher EER means the unit delivers more cooling for the same power, which usually means lower operating cost.
When to use it
Use EER when comparing air conditioners, heat pumps in cooling mode, or other refrigeration equipment rated in BTU/h and watts. It is especially useful for quick performance comparisons at a specific operating condition.
Worked example, step by step
A portable AC unit provides 9,600 BTU/h of cooling and uses 800 W. EER = BTU/h ÷ W EER = 9,600 ÷ 800 EER = 12 So, the unit’s Energy Efficiency Ratio is 12.
Common mistakes to avoid
- Dividing watts by BTU/h instead of BTU/h by watts
- Using cooling capacity in tons without converting it to BTU/h first
- Confusing EER with COP, which uses different units and a different scale
Did You Know?
EER multiplied by 0.293 converts to the dimensionless COP.
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More in HVAC & Refrigeration
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BasicHeat needed to change air or water temperature without a phase change.
Latent Heat Load
IntermediateHeat absorbed or released when moisture condenses or evaporates — the hidden load air conditioners fight.
Coefficient of Performance (Cooling)
IntermediateCooling delivered per unit of work input — higher is more efficient.
Refrigeration Tons
BasicCooling capacity in tons, where one ton removes 12,000 BTU/h.
Airflow (Sensible)
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Carnot COP (Refrigerator)
AdvancedMaximum possible cooling efficiency between two temperatures (in kelvin).