Recently, there has been an increase in the condensation and mould problems of apartment buildings in Korea owing to the high insulation and high air-tightness performance of buildings, which increase energy savings. Condensation is generally found in winter on furniture back panels and adjacent surfaces of the wall, floor, and ceiling. These problems are related to the weather conditions and indoor room conditions in winter. To solve these problems, an auxiliary heating device that can be installed was developed. The purpose of this study was to evaluate condensation risk in the condensation vulnerable areas around built-in furniture of apartment buildings by installing an auxiliary heating device. The experimental results reveal that condensation risk can be reduced by comparing the thermal environment around the built-in furniture with and without installation of an auxiliary heating device in winter. Furthermore, they reveal that it is possible to increase the surface temperature of vulnerable areas around built-in wardrobe by applying an auxiliary heating device to minimize condensation problems by using a minimum device.