•        Sunlight passing through a window adds heat to a room  desirable in winter, but generally unwanted in the summer. Solar heat gain through windows may account for 30 percent or more      of a home's summer cooling requirements.        

•        The amount of heat from direct sunlight through a window is measured with a shading coefficient (SC). The lower the coefficient, the less solar gain heat.                                              

•        Often the best strategy to reduce heat gain in the summer is to provide exterior shading through overhangs, awnings, Shade Screens and trees.

•        When there is a difference between inside and outside temperatures, heat transfers through   a window. It's lost to the outside during the heating season and is gained from the outside during the cooling season.                                                                                                                               

 •        A window's thermal performance - which can be measured at the center of glass, the edge  of glass and the frame - is rated with a U-value, its overall ability to resist heat flow.