How Double Glazed Windows Affect My Electric Bill
Windows improve the exterior and interior appearance of a home. They bring light and fresh air into the home and keep rain, wind and snow out. They can also account for as much as 50 percent of a home’s heating and cooling energy loss. It’s not just drafts from windows that drive up energy costs but the type of glazing used in the windows as well.
The older the windows, the more likely it is that the windows are increasing the household’s electricity costs. Only a couple of decades ago, the windows in most homes were made with a single pane of glass. Single-glazed windows do a poor job at keeping radiant heat out during the summer and at keeping heat in during the winter. Simply replacing single-glazed windows with double glazing can reduce annual energy costs up to 40 percent.
Double-glazed windows are effective insulators, not because the number of panes are doubled but because of the air that’s encased between the two panes. Many manufacturers of double-glazed windows increase efficiency by inserting inert gases like krypton or argon between the panes of glass. Because these gases are denser than air, they make for better insulators.
A low-emissivity (low-E) coating is an extremely thin metallic film that is applied to the glass during the manufacturing process. Depending on how the low-E coating is applied, it can darken the glass or it can be nearly invisible to the eye. Low-E coatings work like two-way mirrors. In the summer, low-E coatings deflect sunlight back outside. In the winter, they reflect heat within the home back inside.
Window Energy-Efficiency Ratings
Window manufacturers rate the energy efficiency of their products in a number of ways. The U-value represents the window’s ability to conduct heat. The lower the U-value, the less heat can be transferred through the glass. R-values measure the window’s insulating ability. Higher R-values mean better insulation. A third rating is the solar heat gain coefficient (SHGC) which measures how much the amount of sunlight that hits a window is actually transferred indoors as heat.
Energy Star Label
While the ratings provided by window manufacturers can be helpful in choosing windows according to specific climates, consumers can simplify choices by shopping for windows that carry the Energy Star logo. For windows to qualify for the U.S. Department of Energy’s Energy Star label, they must be 15 to 40 percent more energy-efficient than windows commonly used in home construction.
Even in a well-heated home, a drafty window causes discomfort. Energy-efficient windows not only save homeowners money on heating and cooling costs but help makes home feel more comfortable as well. You can take your time and look around a double glazing price guide.