How is efficiency rated for geothermal?

Heating and cooling systems carry an efficiency rating which is certified by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). Fossil fuel furnaces use AFUE. Air conditioners use SEER while heat pumps use HSPF and SEER.

Geothermal heat pumps rate heating efficiencies according to their coefficient of performance, or COP. It’s a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have COPs of 3-4.5.

For cooling, geothermal units are rated in Energy Efficiency Ratio (EER). This is a measure of the instantaneous energy efficiency of cooling equipment. The higher the EER, the more efficient the unit.