EER stands for Energy Efficiency Ratio (also commonly expressed as Energy Efficiency Rating), measure the efficiency with which a product uses energy to function. It is calculated by dividing a product's BTU output by its wattage.
How is EER calculated?
The Energy Efficiency Ratio of a heating or cooling system is usually calculated by dividing the heat output of the system by the power input.
The EER rating for an air conditioner is calculated by dividing the BTU (British Thermal Units) rating by the wattage.