Weary 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, your air conditioner must work harder to cool hot air from sunny windows. Install Energy Star windows and use curtains and shade to give your air conditioner and energy bill a break. If you live in the Sun Belt, look into low-e windows, which can cut the cooling load by 10% to 15%.

If your home has single-pane windows, as many U.S. homes do, consider replacing them with new double-pane windows with high-performance glass (e.g., low-e or spectrally selective). 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 they allow you to buy smaller, less expensive heating and cooling equipment.

Here are a few shopping tips when purchasing your new windows:

• Look for the ENERGY STAR label.

• Check with local utilities to see what rebates or other financial incentives are available for window replacement.

• High-performance windows have at least two panes of glass and a low-e (low emissivity) coating.

• Remember, the lower the U-factor, the better the insulation. In colder climates, focus on finding a low U-factor.

• Low solar heat gain coefficients (SHGCs) reduce heat gain. In warm climates, look for a low SHGC.

• In temperate climates with both heating and cooling seasons, select windows with both low U-factors and low SHGCs to maximize energy savings.

• Look for whole-unit U-factors and SHGCs, rather than center-of-glass, or COG, U-factors and SHGCs. Whole-unit numbers more accurately reflect the energy performance of the entire product.

• Have your windows installed by trained professionals. Be sure they're installed according to manufacturer's instructions; otherwise, your warranty may be void.