This study deals with the design strategies of Ondol heating system which satisfy the thermal need of the aged in welfare facilities. A literature survey was conducted to investigate the physiological characteristics of the aged, the existing studies on thermal comfort were examined. The experiment on thermal comfort for the aged was conducted in a model setting which could simulated the precise Ondol heating system. A the same time questionnaire survey was conducted in order to find the subjective responses regarding to thermal comfort. Based on the result of the above, the optimum Ondol design strategies of welfare facilities for the aged were presented.