Traditional window materials used in houses across the United States – old single-pane and later double-pane clear glass – do a poor job of keeping out the cold and excessive heat. If you have these windows in your home, you are likely spending hundreds of dollars a year more in home heating and cooling costs than you would with the latest ENERGY STAR® -qualified windows.
Replacing old windows is a financial investment, but the payback in terms of improved comfort, reduced energy usage, and money saved over the long term makes replacement a smart choice. Upgrading to ENERGY STAR®-qualified models can save you as much as 7-15 percent or more on annual household energy bills, depending on your geographic location and the type of window being replaced. Before replacing your windows, be sure you have already properly insulated and air sealed your home.
When purchasing ENERGY STAR®-qualified windows, look for the U-Factor and the Solar Heat Gain Coefficient (SHGC). The U-Factor measures how well the window insulates. While the U-Factor can be any value, in general for windows it ranges from 0.20 to 1.20. The lower the U-Factor, the better the window insulates. The SHGC measures how much of the sun’s heat comes through the window. The SHGC typically runs between .25 to .80. The lower the SHGC, the less solar heat the window lets in.
Source: Energy.gov
