In this study, the conditions for coupling thermal and hydronic simulation together were investigated. Based on these conditions, a coupled model was developed using Matlab/Simulink. The simulation result by a developed model was compared to that by conventional simulation method which assumes that each room is supplied with the fixed design flow rate. The results were compared to each other in terms of thermal comfort and energy efficiency. Thermal comfort was evaluated by the varying the room air temperature and the energy efficiency were examined by supplying heat to the room.