In other words, nearly 20 times more heat escapes through each square foot of window than through an insulated wall. With this R, the product has about 75 percent efficiency, which means it stops 75 percent of the heat loss through the window. Table 1 below lists the R factors of various window types. Heat losses occur by infiltration when there are cracks around the frame or glass. Heat is conducted through glass rapidly when it warms the glass and is transmitted to the colder outside environment.
Radiation is the process of losing heat through space.
For example, a person seated near an uncovered window will begin to chill as their body heat radiates to cold glass surfaces. Insulation value of windows and window treatments. The Inside Story , Gwen Cukierski. The first step in your management plan should be to correct infiltration problems. This can be done with caulking, weather-stripping or a combination of storm windows.