Abstract: A swimming pool heating system which utilizes a heat pump that is used for heating heat transfer fluid which is circulated through the primary coil of a heat exchanger. The pool water is circulated through the secondary coil of the heat exchanger by means of a standard pool pump. Rather than heating all of the water which is handled by the pump, a system bypass line is connected to the pool outlet line and a diverter valve, which is located in the pool return line, is used to divert a portion of the circulated pool water to the heating system. A three-way regulator valve located in the system bypass line divides the diverted pool water, directing a selected portion of it to the heat exchanger and a selected portion of it to the pool return line in order to automatically control the heating effect the pool heater has on the heat transfer fluid, thereby keeping the discharge pressure of the heat pump relatively constant so that it operates in its most efficient range.