Heat pump with supplemental heat source

A heat pump includes a compressor having an inlet and an outlet, an indoor heat exchanger and an outdoor heat exchanger, and an outdoor thermal expansion valve. The heat pump further includes an auxiliary heat exchanger. An auxiliary fluid line and an auxiliary fluid pump circulate an auxiliary heat transfer fluid through the auxiliary fluid line. The compressor outlet, the indoor heat exchanger, the outdoor thermal expansion valve, the auxiliary heat exchanger, the outdoor heat exchanger, and the compressor inlet can be placed in respective serial fluid communication to thereby circulate a refrigerant fluid through the heat pump. The auxiliary heat exchanger is configured to exchange heat between the refrigerant fluid and the auxiliary heat transfer fluid. The auxiliary fluid line is in thermal energy communication with a primary source of auxiliary heat. Preferably, the primary source of auxiliary heat is a fluid contained within a septic tank.