In water purifiers, 65% of energy is used to maintain hot water. The purpose of this study is to improve existing problems after the introduction of instantaneous hot water to the 2011 water purifier. Conventional surface heater is composed of plate type. In addition, since it is constituted by a quadrangle, it is difficult to form a channel inside. If the internal flow path is not formed, smooth heat exchange becomes difficult. For this purpose, we will discuss the improvement of the analysis and practical application of the internal flow path using a cylindrical surface heating heater.