Installing the right windows in your house reduces the amount of energy you use in heating and cooling your home. It is not only an eco-friendly thing to do, but will save you money on your utility bills over time. The exact window you choose depends largely upon where you live. The U.S. Department of Energy and the Environmental Protection Agency have divided the country into four climate zones, each with different heat-transfer requirements. Windows that meet these requirements come with an Energy Star label that designates the window as approved for a certain region.
The northern zone encompasses most of the country, from Alaska and Maine as far south as mid-New Mexico and Arizona. The north-central zone starts in the middle of New Jersey and in Northern California, and continues south. The south-central zone includes the rest of California on the west coast, but begins in the middle of North Carolina on the east coast, extending to the southern Georgia border and the middle of Texas. Everything south of that point is in the southern zone, including Hawaii and the Florida Keys. Visit the Energy Star website to find your zone before you shop for windows. (See References 1)
Your zone, the U-Factor and the Solar Heat Gain Coefficient of your windows are interrelated. The U-Factor refers to the amount of heat that can pass through the window from inside to outside. In colder climates, this should be minimal to help with heating; in warmer climates, this helps with cooling. The SHGC refers to the amount of heat that can pass through the window from the outside to the inside, and should be the opposite of the U-Factor. For example, a house in Vermont is in the northern zone, so the windows should have a U-Factor of 0.30 or less to minimize heat loss, but a SHGC of over 0.35 to allow as much solar heat in as possible. On the other hand, a home in Florida should have windows with a U-Factor of 0.60 to allow heat to leave the home, but a SHGC of 0.27 or less to minimize the incoming heat. (See References 1 and 2)
Energy-efficient windows have multiple panes of glass -- usually two, but sometimes three or more -- with each additional pane providing extra impact resistance. Air or nontoxic gases, such as krypton and argon, fill the spaces between the panes, to help with insulation. Spacers placed in the frame between the panes keep the panes apart. To provide higher insulation capabilities, do not use metal spacers. Chemicals that reflect infrared and ultraviolet light coat the panes to help with energy savings, and keep your furniture from fading. (See References 2)
There are several framing materials available for energy-efficient windows, each with advantages and disadvantages. Fiberglass frames offer good insulation on their own, and can have foam filling for added protection. Aluminum frames are durable, and typically made from 15-percent recycled content (see References 2). Wood frames may be preferred in historic neighborhoods, with the outside covered in vinyl or aluminum to cut down on weathering. You can even use different materials for different parts of the frame to optimize performance for your particular home.