While there are a wide variety of window frame materials from which you can choose, including wood, vinyl, aluminum, and fiberglass, one of the most important decisions you can make involves the glass within the window frame. The energy efficiency of a window is determined in large part by the nature of the glass within the window; many experts estimate that as much as 30% of the heat loss from the average home is due to the glass windows.
Historically, windows have been available in only a single-pane, clear glass version. In current times, it is difficult to find single-paned clear glass windows because so many technological advances have been applied to window glass. More modern windows glass offers multiple benefits, including energy efficiency in both hot weather and cold and control over how much light enters the room.
Modern replacement windows usually have two or even three panes of glass. Two panes help to slow the heat transfer through glass windows, and three panes slow it even further. As you might expect, three panes cause a window to be more expensive as compared to a window with two panes, so it becomes a trade-off between paying more for the initial cost of the glass window versus reaping the lower utility bills over time.
Double- or triple-paned glass windows offer improved energy efficiency due to the air trapped between the panes. Some window manufacturers offer windows with colorless argon or krypton gas infused between the panes of glass, as either gas improves the insulating properties of the window. Both argon and krypton are harmless gasses that are naturally present in the earth's atmosphere, so if the window were to break, there is no danger posed by the release of the gas.
Another technological improvement in window panes is a coating known as Low-emission, or Low-E. This involves applying an ultra-thin layer of metal or metal oxide to the surface of a glass window which helps to reflect heat from the sun when the outside temperature is high and assists in retaining the heat inside the house when the outside temperature is low. LowE2 and LowE3 coatings are similar to Low-E, but are even more energy-efficient.
Impact-resistant glass windows are an option that can increase safety in areas that are susceptible to high winds and airborne debris. The strongest construction for impact-resistant glass consists of two panes of glass with a shatterproof membrane between them. These windows are particularly helpful in regions that are prone to dangerous weather patterns.