# How to Convert an EER to a COP

The coefficient of performance and the energy efficiency ratio measure the efficiency of air conditioners and heat pumps. Heat pumps are rated by EER when used as an air conditioner and COP when used for heat. The higher the EER and COP, the more efficient the system. COP is a unitless measure. It is the energy acquired or heat produced divided by the energy applied. The EER is expressed in British thermal units per watt-hour. It is the cooling capacity divided by the energy applied. To convert from EER to COP, divide by the conversion factor 3.413; to convert from COP to EER, multiply by 3.413.

## Step 1

Get the EER. It should be on the cooling system's yellow EnergyGuide label, which manufacturers are required to display on many appliances. This label lists how much energy the appliance uses, compares the energy use of similar products and indicates the approximate annual operating costs. According to the US. Department of Energy, national appliance standards require room air conditioners to have an EER in the 80 to 98 or greater range, depending on the type and capacity.

## Step 2

Convert the EER to COP. Divide the EER by 3413 to get COP. For example, if the EER is 45 Btu/watt-hour, then the COP is about 132, the result of 45 divided by 3413.

## Step 3

Multiply the COP by 3413 to get the EER. For example, if the COP is 15, then the EER is about 512 Btu/watt-hour because that is the total of 15 times 3413.