This paper presents a mathematical model and the results of numerical simulations of a double sheet ventilated glass window. The incident solar radiation heats up the air between the glass sheets creating buoyancy forces that induces upward flow of air. The two-dimensional transient model is formulated based upon the fundamental equations of mass conservation, momentum and energy, the associated constant and time varying boundary conditions and is solved by finite difference approach and the ADI (alternating direction implicit) scheme. The numerical grid and the time increment were optimized and the numerical results were validated against available data. Results of the temperature field along and across the channel are obtained for different spacing between the glass sheets and incident radiation conditions. The effects on the solar heat gain coefficient and the shading coefficient were also presented and discussed. (C) 2004 Elsevier Ltd. All rights reserved.