Windows are critical to building energy efficiency because they are often the weakest link for heat transmission through the building shell, allowing heat loss in cold climates and heat gain in hot climates. Energy-efficient windows can provide lower heating, ventilation and cooling costs; improve comfort; increase natural daylight and enhance your view; reduced sunlight damage to furnishings; and reduce or eliminate window condensation.

Energy-efficient windows can filter out 40% to 70% of the heat from sunlight, and can reduce building energy use by 20% to 30%. The key components — glazing, sash and frame — are available in a variety of designs that use a broad range of materials. For more information, visit the DOE Buildings program Web site.

The U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy collaborate in the Energy Star program, a voluntary labeling program designed to identify and promote energy-efficient products to reduce greenhouse gas emissions. The Energy Star Web site provides useful information on thousands of these products, including windows.

DOE's "Consumer's Guide to Energy Efficiency and Renewable Energy" has excellent information on energy-efficient windows, doors, and skylights.