In this paper we report the results of coupled DOE-2 and 3D transient computational fluid dynamics (CFD) simulations for an unconditioned 100-year-old Buddhist temple, located in an urban area of Bangkok, Thailand. The HEATX CFD code was combined with the DOE-2 thermal simulation program, to analyze the heat transfer and airflow performance of the building. The indoor temperatures simulated by both programs were validated with measured temperature taken at the site. The simulation indicated poor thermal comfort conditions in this temple. The transient CFD/DOE-2 simulation suggested several remedial changes that could be implemented to improve the indoor comfort. In addition, a prototype building that combined several improved design options was proposed, and the simulation of the prototype was then performed. The result indicated an improvement of the indoor thermal comfort compared with that of the current building. (C) 2004 Elsevier B.V. All rights reserved.