Geothermal Heat Pump Manuals & Owner Guides

Ground loop types explained

Closed loop — vertical

Boreholes, often 150–500 ft deep, hold U-shaped plastic pipe filled with water and antifreeze. Needs little land; drilling is the main cost.

Closed loop — horizontal

Pipe laid in trenches typically 4–6 ft deep. Cheaper to install where there is enough open land.

Closed loop — pond

Coils sunk in a pond or lake of adequate size and depth.

Open loop

Groundwater is pumped from a well, passed through the heat pump and returned to a second well or an approved discharge. Efficient where water is plentiful and clean, but regulated in many areas.

Direct exchange (DGX)

Refrigerant circulates through buried copper tubing, eliminating the water loop and its pump. Requires suitable, non-corrosive soil.

Reading EER and COP ratings

Geothermal heat pumps are rated with EER (cooling Btu per watt-hour) and COP (heat delivered per unit of electricity) at fixed entering-water temperatures defined by ISO 13256. Closed-loop ratings assume 77 °F fluid in cooling and 32 °F in heating; open-loop ratings assume 59 °F and 50 °F groundwater. Because the conditions differ, compare closed-loop models only with closed-loop models and open-loop with open-loop.

Geothermal EER values are not directly comparable with the EER or SEER2 of an air-source air conditioner, which are measured with 95 °F or varying outdoor air.

Water-to-air or water-to-water?

Water-to-air units have an indoor blower and coil and connect to ductwork, replacing a furnace and central air conditioner. Water-to-water units heat (and sometimes chill) water for radiant floors, fan coils or a buffer tank, and pair well with hydronic systems designed for low supply temperatures.

Geothermal Heat Pump FAQ