Energy Savers: Windows

Windows can be one of your home's most attractive features. Windows provide views, daylighting, ventilation, and solar heating in the winter. Unfortunately, they can also account for 10% to 25% of your heating bill. During the summer, sunny windows make your air conditioner work two to three times harder. If you live in the Sun Belt, look into new solar control spectrally selective windows, which can cut the cooling load by more than half.

If your home has single-pane windows, as almost half of U.S. homes do, consider replacing them. New double-pane windows with high-performance glass (e.g., low-e or spectrally selective) are available on the market. In colder climates, select windows that are gas filled with low-emissivity (low-e) coatings on the glass to reduce heat loss. In warmer climates, select windows with spectrally selective coatings to reduce heat gain. If you are building a new home, you can offset some of the cost of installing more efficient windows because doing so allows you to buy smaller, less expensive heating and cooling equipment.

If you decide not to replace your windows, the simpler, less costly measures listed below can improve the performance of your windows.

Cold-Climate Window Tips

• Install exterior or interior storm windows; storm windows can reduce your heat loss through the windows by 25% to 50%. Storm windows should have weatherstripping at all moveable joints; be made of strong, durable materials; and have interlocking or overlapping joints. Low-e storm windows save even more energy.
• Repair and weatherize your current storm windows, if necessary.
• Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
• Close your curtains and shades at night; open them during the day.
• Keep windows on the south side of your house clean to maximize solar gain.

Warm-Climate Window Tips

• Install white window shades, drapes, or blinds to reflect heat away from the house.
• Close curtains on south- and west-facing windows.
• Install awnings on south- and west-facing windows.
• Apply sun-control or other reflective films on south-facing windows to reduce solar gain.

Buying New Windows

New windows are long-term investments that have a large impact on your home's energy systems. Today, there are many new window technologies available that are worth considering. Glazing materials now come with a variety of selective coatings and other features; frames are available in aluminum, wood, vinyl, fiber glass, or combinations of these materials. Each type of glazing material and frame has advantages and disadvantages.

Shopping Tips

• When you're shopping for new windows, first, look for the National Fenestration Rating Council (NFRC) label; it means the window's performance is certified.
• Remember, the lower the U-value, the better the insulation. In colder climates, a U-value of 0.35 or below is recommended. These windows have at least double glazing and low-e coating.
• In warm climates, where summertime heat gain is the main concern, look for windows with double glazing and spectrally selective coatings that reduce heat gain.
• Select windows with air leakage ratings of 0.3 cubic feet per minute or less.
• In temperate climates with both heating and cooling seasons, select windows with both low U-values and low solar heat gain coefficiency (SHGC) to maximize energy benefits.

For more information about windows, contact:

American Architectural Manufacturers Association (AAMA),
(847) 303-5664

ENERGY STAR®,
(888) STAR-YES (782-7937)

National Fenestration Rating Council (NFRC),
(301) 589-6372

National Wood Window and Door Association,
(800) 223-2301

Owens Corning Customer Service Hotline,
(800) GET-PINK (438-7465)

U.S. Department of Energy's Energy Efficiency and Renewable Energy Clearinghouse (EREC), (800) DOE-EREC (363-3732), and Network (EREN).