Abstract: A water heater includes a tank and a heating pipe. The tank has a water storage space therein. A bottom of the tank is provided with a cold water inlet and a circulation outlet. The tank is provided with a hot water outlet located at a position not less than one half height of the tank. The heating pipe is connected with a circulation pipe outside the tank to communicate with the circulation outlet. The heating pipe extends upward from the bottom of the tank into the water storage space. The heating pipe is provided with an opening facing sideways. The opening is located at a certain height of the water storage space. An outside of the heating pipe is provided with a heating device for heating the heating pipe.