Abstract: A heat transfer system for transferring heat into a first body of water flowing through a first conduit (20, 22, 24) from a heated second body of water (12) that is flowing through a second conduit (14), the two conduits being contiguous to each other. A pump (26 or 62) operates to force the second body of water through the second conduit. A motor (32 or 60) is so connected to the pump as to operate the pump when the motor is actuated and an arrangement is provided to actuate the motor in response to the flow of the first body of water through the first conduit.