Free water surface may generate excessive moisture and heat and have adverse effects on indoor environment and energy loss. A series of experiments have been carried out to study the characteristics of indoor temperature and moisture distributions using a free water surface within a test chamber. Some parameters such as air change rates, surrounding air temperature and humidity, water temperature and water surface area, were chosen to find their influences on simultaneous moisture and heat transfer. In addition, a new method for determining the simultaneous heat and mass transfer rates from free water surface is developed. Using this method with connection of CFD simulations, the moisture-related problems due to free water surface can be predicted precisely. (C) 2004 Elsevier B.V. All rights reserved.