KOTATSU is a well-known heating facility in Japan. It heats the lower extremities of a body by an infrared heater or wood coal fire in a box. The objective of this paper is to clarify the thermal effect of KOTATSU on a person. Experiments were carried out under the following combined conditions: air temperatures were 11℃, 14℃, 17℃, and 20℃ and infrared lamp levels were 'off', 'low', 'middle' and 'high' which correspond to 0W, 87W, 91W and 181W infrared heater electric consumption, respectively. Five male subjects participated in those experiments. The following results were obtained: 1) The mean skin temperature at the lower extremities of the body rose and that at the upper extremities dropped respectively, while a subject was seated at the KOTATSU. 2) The corrected operative temperature to indicate the thermal effect of KOTATSU was introduced by the authors in the basis of heat balance equation of the human body. This index correlates with the modified mean skin temperature and the thermal sensation. Consequently, it is a suitable index to evaluate the thermal environment while a subject is seating at the KOTATSU.
