Ondol heating, a kind of radiant floor heating, is the main form of heating being used in housing units in Korea. Although Ondol can provide a more comfortable and healthy indoor environment than any other form of heating systems, a more precise simulation is required to further improve the system to prevent over and under heating of the housing environment. However, due to complexity, building energy simulation has so far not been performed, for systems such as Ondol and other relevant facilities. For evaluating energy consumption and indoor temperature variation, a new method has been proposed. In this study, a dynamic simulation of Ondol heating was carried out by combining TRNSYS and EES. This new system of building simulation could contribute to determine over or under heating of the system in a housing unit. The simulation results of a typical housing unit in Korea showed a good trend in a viewpoint of actual behaviour of Ondol heating, maintaining a comfortable and healthy indoor environment with less energy consumption. Nomenclature