Windows With Low-E Glass Levels

How It Works

• The coating on low-E windows is made from metal or metal oxide, which adheres to one or both surfaces of the window glass. In double-glazed windows, one or both of the panes may have low-E coatings. The coating works by reducing infrared radiation through the glass. If you apply a low-E coating to the outside of a window, it will restrict outdoor heat from entering the house. On the other hand, coating the interior side of a window keeps heat from passing from inside to outside.

Pyrolytic and Sputtered Low-E Windows

• Low-E windows may have either pyrolytic low-E or sputtered low-E coatings. In pyrolytic low-E windows, tin oxide is applied to the window while the glass is still hot, baking it in very durably. By contrast, sputtered low-E windows have one to three layers of silver enclosed within multiple panes. Because the silver coating on sputtered low-E windows cannot be exposed to the air, its use is usually restricted to double-glazed windows.

Solar Gain

• The solar gain of a window refers to how much heat it allows to enter the home. In a hot climate, you typically want a window with a low solar gain, whereas a high solar gain is ideal in cold, northerly climates. The same principle applies depending on where a window is oriented. Regardless of your local climate, if you have a south-facing window that brings too much heat into a small room, you may opt for a window with a relatively low solar gain. Low-E glass windows are available with all levels of solar gain. All of them reduce heat loss from inside to out, but they vary in how much heat they allow to enter the home.

Visibility

• If you're interested in cutting down on heat transfer, but you're concerned about keeping your home brightly lit, opt for a low-E window with high visibility. Depending on the level of solar gain you choose, a low-E window may permit anywhere from 75 to 64 percent of all visible light to shine through. Windows with high solar gain, which permit the most heat to enter your home, also allow the most light in.