Using finite elements, the authors studied temperatures and thermal stresses in 1.41 m wide by 2.12 m high sealed double-glazed windows of 6-mm glass with a 12-mm air space between the panes. The purpose was to find factors significantly influencing thermal stresses. Three types of commercially used windows subject to winter conditions (day and night) were analysed: both panes clear glass; outer pane heat absorbing and inner clear; and outer clear with a metallic film on its room-side surface and inner clear. A sensitivity analysis included variations in size of window, gasket and sealant stiffnesses, frame absorption, solar heat flux, exterior air film conductance, and outdoor air temperatures (−5 and −25 °C). Further, the influence of horizontal and vertical shadows was studied. For the calculation of thermal stresses, the authors found that the windows could be analyzed pane by pane rather than as a three-dimensional structure. Solar radiation and particularly shadows had a major influence on thermal stress, while window size and aspect ratio did not. A case study in which the predicted temperatures were compared with those measured by Sasaki in 1974 showed good agreement and indicated that a simpler steady-state rather than transient thermal analysis gave a close estimate of the temperature difference between the centre and edges of panes for design against thermal breakage. Key words: window breakage, thermal stresses, glass temperatures, shadows, double-glazing, finite elements.