How energy efficient is my geothermal system?

Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated 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 (WaterFurnace's E Series is rated up to 4.7). That means for every unit of energy used to power the system, 3-4.5 units are supplied as heat. Where a fossil fuel furnace may be 78-90 percent efficient, a geothermal heat pump is about 400 percent efficient.