A geothermal heat pump (GHP) system with three ground coils was installed in a residence in northern Idaho with a portion of the ground heat exchanger wrapped around the residential septic tank. The septic coil provided a significant portion of the heating for the residence over the heating season. There was no evidence of the septic tank freezing up or failing to properly function. Utilizing a septic tank as a heat source for GHP systems is feasible design option if the septic tank is used on a full-time basis. However, the tank should be surrounded on all sides by a large amount of soil and/or insulated from the ground surface to ensure that ground temperatures near the tank remain warm during the winter.

Hanegan, T., 1996, “Feasibility of Using a Septic Tank as a Heat Source for Geothermal Heat Pumps,” Master’s Thesis, University of Idaho, Moscow.
Wallace, A., 1995, Professional Engineer and Professor of Civil Engineering, University of Idaho, Personal interview.
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