Water heater

A water heater consists of a heating device and a water storage device. The heating device is arranged on gas furnace and is equipped with a cold water pipe and a hot water pipe; a heating water pipe is positioned between a cold water pipe and a hot water pipe, and the heating water pipe is wound on upper part of end of the gas furnace in a loop shape; the cold water pipe is provided with a switch structure which can control the ignition and the water intake. The water storage device has a water storage barrel which is connected with the hot water pipe. Residual heat around the furnace end can heat the heating water pipe, Hot water is stored in the water storage barrel, thus the water heater not only is effective in saving energy, but also is low in cost and durable with simplified structure and easy installation.