The flow and heat transfer characteristics of a triple-glazed exhaust airflow window system were studied numerically by using the finite-volume method. Exhaust airflow rate, solar insolation and aspect ratio were considered important parameters. It was shown that space-heat gain was reduced considerably by increasing the exhaust airflow rate. The optimum exhaust airflow rate and aspect ratio were suggested to be Re = 600 and W/H = 0.05, respectively. Some comparisons between the airflow window system and the enclosed window system were made qualitatively and quantitatively. Copyright (C) 2002 John Wiley Sons, Ltd.