Closed-loop, ground-coupled systems use a vertical or horizontal heat exchanger buried below the frost line to collect or reject heat. This heat exchanger circulates water in a closed loop to reject or collect heat from the ground, lake, or pond. The water may be treated to prevent freezing and to reduce corrosion and scaling.

Horizontal loop installations are placed in 4 to 6 foot deep trenches with trench lengths running from 120 to 190 feet of trench per ton, depending on the coil type and the soil conditions. The horizontal slinky coil requires the least trench length but has a higher pipe cost per foot of trench. Vertical heat exchangers need about 150 to 250 feet of bore hole per ton and U-tube loops are typically installed in bore holes 150 to 200 feet deep.

Ground-coupled heat pump systems are most appropriate where land is available for burying the pipe and soil conditions are suitable for easy excavation or drilling. However, material and installation costs should always be estimated for your situation since general guidelines can be misleading.