How is efficiency rated for geothermal?

All heating and cooling systems have a rated efficiency from a U.S. government agency. 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. The WaterFurnace Envision holds the highest recorded certified performance of 5.4 COP in an open loop. That means for every dollar of energy used to power the system, $5.40 of energy are supplied as heat. Where a fossil fuel furnace may be 78-98% efficient, a geothermal heat pump is about 500% efficient.

For cooling, geothermal units are rated by Energy Efficiency Ratio (EER). EER is a measure of efficiency in the cooling mode when measured at a constant temperature (95 degrees F). The higher the EER, the more efficient the unit. The WaterFurnace Envision holds the highest recorded certified performance of 30EER for closed loop and 32.1EER for open loop.