Downhole heat exchangers (DHE's) have been used extensively in Klamath Falls, Oregon, and there are a few installations elsewhere. However, they have not been used in the city of Calistoga. This study addresses the conceptual design of a DHE and geothermal well, DHE testing, and technical and economic feasibility of DHE-based space heating and cooling system for a six-unit condominium. The study concludes that a heating/cooling system is technically feasible. A heating system shows a satisfactory payback; however, space cooling does not appear to be economically attractive