Poor insulation leads to huge amounts of energy - and money - going out the window (and through the walls, etc.) Caulking and weather-stripping can save an estimated 650 lbs of CO2 per year!

Windows can account for as much as 25 percent of home heat loss. Sealing the windows properly can prevent about half that loss. The remaining loss is as a result of the direct flow of heat from the panes of conventional windows.

Source: Canadian Green Consumer Guide