The Best Soil Conditions for Ground Source Heat Pumps

Depth

• Depth refers to how much soil you have. The more soil -- the thicker the layers are -- the better. When the soil layers end, then stony ground like bedrock or frozen earth (in colder climates) begins. Installers cannot put heat pumps in bedrock; they need to work with loose soils. Deep soils and earth layers that persist underneath the house foundation are the best.

Room

• The earth space below the house is often contested ground, used by a variety of systems including sprinklers and septic pumps. There may not be room to easily install a ground source heat pump, especially a horizontal version. Many types of soil also have large rocks that may present problems in rougher conditions. The more room there is in the soil, the more easily you can install a geothermal unit.

Heat Transfer

• Heat transfer refers to the soil's ability to easily move heat from one place to another. In general, tight and compact soils like clay have low heat transfer abilities and can only move heat slowly, making them difficult to use for ground source heating. Looser soils that can transfer heat quickly are better, allowing the pipes to quickly absorb energy.

Stability

• Stability refers to how easily the soil can shift. Loose soils are good, but if the soil is too loose, then erosion or shifting may be a problem, causing pipes to crack or become loose. Sandy soils are often unsuitable for geothermal units, but professional contractors should be able to tell if the soil at a house can shift too easily for the system.