A water heater using a planar heating element according to the embodiment of the present invention comprises a planar heating pipe coated with a planar heating material; a hot water tank including an upper surface coupled with the planar heating pipe where a first hole and a second hole are formed, a side surface surrounding an outside of the planar heating pipe where an outlet is formed, and an open lower surface; a first header provided at the upper surface to form a first housing; and a second header provided at the other end of the planar heating pipe and the open lower surface to form a second hosing where an inlet coupled with the other end of the planar heating pipe is formed. Wherein the first housing is a space defined by an inner surface of the first header and the upper surface of the hot water tank, and the second housing is a space defined by an outer surface of the planar heating pipe, an inner surface of the hot water tank, and an inner surface of the second head.