Abstract: A heat exchanger system for utilizing the exhaust gases of an internal combustion engine to heat liquid. A system for heating water to be used in a carpet and furniture cleaning system is disclosed. A pump circulates water from a holding tank through a serial circuit including copper coils wound around primary exhaust pipes from an engine to a primary heat exchanger and a secondary exhaust pipe from the heat exchanger to the remainder of the exhaust system. The circuit includes the primary heat exchanger which comprises concentric copper tubes forming a water jacket therebetween. The exhaust gases enter the inner tube adjacent opposite ends and a deflector plate adjacent each entry causes a helical passage of the exhaust gases from either end along the inner tube in a manner causing maximum turbulence so as to maximize heat transference to the wall of the inner tube and thus the water jacket. The secondary exhaust pipe exits the exhaust gases mid-way between the ends of the heat exchanger.