To make efficient use of energy with an equipment using a thermoacoustic phenomenon and realize a small water heater with high energy efficiency.

Heat exchange units having a resonance pipe in an U shape and further having a stack and heat exchangers on both the sides thereof are arranged at two places at a close end side of the resonance pipe and a bent part side. The heat exchange units are configured in such a manner that heat from combustion gas enters the heat exchange unit at the close end side to generate acoustic vibration in the resonance pipe and the heat exchange unit at the bent part pumps heat from outside air utilizing the vibration so that water is supplied and heated in the respective heat exchange units and in an exhaust gas heat exchanger as well.