How Window Screens Affect Winter Fuel Use in Heating Climates
Next, I placed three pieces of dark soapstone (12 x 12 x 1/2 tiles) near a window facing south, on a sunny March day around noon. One piece was placed in the shade, one in direct sunlight (through the window), and one with the screen in the window. I came back and measured the temperatures of the three stones with an infrared thermometer from a distance of about 1 foot. The shaded stone measured 76.7ºF, the one in the screened window 88.7ºF, and the one in the unscreened window 96.7ºF.
From this it would appear that leaving screens in windows or storms during the winter block about 30-40% of the heat that would otherwise enter through the windows. Audits have the amount of heat obtained from passive solar through windows ranging from 10-25% of the fuel based heating. So, window screens represent somewhere between 3-10% of total fuel.Of course, in climates and seasons where solar gain isn't wanted, there's an inverse corollary. There are interior and exterior window shades listed in GreenSpec. The section introduction says:
Window shades, blinds, and other treatments can control daylight penetration and significantly reduce heat loss or heat gain through windows. In commercial buildings, engineered window shading installations can be part of an integrated design strategy addressing glare, heat gain, and solar penetration. In residential buildings, insulating window blinds and quilts may be appropriate retrofits for older, leaky windows, when window replacement can't be justified. In new construction or when replacement can be justified, installing high-performance windows is usually a better option than investing in energy-conserving blinds or shades.
(2009, January 20). How Window Screens Affect Winter Fuel Use in Heating Climates. Retrieved from https://www.buildinggreen.com/blog/how-window-screens-affect-winter-fuel-use-heating-climates