In addition to the difference between traditional Thai and modern western houses, the comfort expectations of westerners and the Thai may be different. Ht is important to understand the Thai's thermal comfort expectations in order to design a proper ventilation system. The ASHRAE Standard 55a-1995 on Thermal Environmental Conditions for Human Occupancy'' gives the upper limit of comfortable temperature as 26oC, and the wet bulb temperature upper limit as 20oC [1], as shown in Fig. 2. However, many studies have concluded that the comfort temperature is higher in tropical regions, since humans have the ability to acclimatize and/or have physiological variation [2]. Field study results show the discrepancies between thermal comfort requirements of the Thai people and westerners. Busch's study [3] shows that, based on 80% of Thai workers being satisfied, the upper limit of the comfortable temperature can be as high as 28oC for people in air-conditioned buildings, and 31oC in naturally ventilated buildings.