By finite difference calculations the convective flow in a vertical enclosure heated from a side is investigated. The emphasis in the study is for the flow of air in a window cavity. Detailed plots of the stream patterns and isotherms in a multicellular flow are shown and vertically averaged Nusselt numbers as well as typical local values are given. The calculations compare favorably with the experiments of ElSherbiny, Raithby, and Hollands. A working formula for window spacings is suggested.