Volumetric energy saving gas water heater

The utility model provides a positive-displacement energy-saving gas water heater which comprises a casing, a heat exchanger, a combustor, a water inlet pipe, a water outlet pipe and a water outlet pump, wherein a storage water tank is arranged on the upper part in the casing, and a working chamber is arranged on the lower part in the casing; the heat exchanger and the water outlet pump are installed in the working chamber; the combustor is arranged on the lower part of the heat exchanger; a residual heat exchange case is arranged in the water storage tank, and a longitudinal heat exchange pipe is arranged in the residual heat exchange case; the heat exchanger is provided with a plurality of flue pipes which are communicated with the residual heat exchange case, and a smoke exhaust pipe which is arranged at the top part of the residual heat exchange case extends outside the casing; the water inlet pipe is communicated with the water storage tank, a water inlet of the water outlet pump is communicated with the water storage tank and a water outlet of the water outlet pump is communicated with the water outlet pipe. A circulation water pump is arranged in the working chamber, a water inlet of the circulation water pump is communicated with one side of the water storage tank, and a water outlet of the circulation water pump is communicated with a water inlet of the heat exchanger; a water outlet of the heat exchanger is communicated with the other side of the water storage tank. The utility model which has the advantages of low cost convenient installation and operation is used for the concentrated supply of hot water.