Drag reduction by use of cationic surfactant solutions is considered to be an e effective way to reduce the running cost of a closed-loop air conditioning system. Many practical applications of the drag-reducing technique have been widely adopted in Japan. However, by analogy with the case of momentum and heat transfer, it has been predicted that heat transfer reduction would occur simultaneously with drag reducing flow, although no problems of heat transfer reduction have been reported in these applications. In this study, in order to propose suitable preparation conditions for use of cationic surfactants and to evaluate the heat transfer characteristics of the air condition system, the drag reduction and heat transfer reduction caused by two kinds of cationic surfactants were measured during the heating operation of the system.