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February 27, 2012

Alli @ 8:23 am

Windows – Energy Efficency


Besides offering a view while washing dishes, windows provide natural light and reduce the need for electricity. The same applies to skylights, patio doors, and entry doors with glass panels. Maximizing the use of natural light to save energy and to make your home more comfortable is also called day-lighting. Day-lighting takes into account window placement and coverings as well as the windows themselves.

On the other hand, windows can be a major source of heat loss in winter and heat gain in summer, forcing you to overwork your furnace and your air conditioner. Old or poorly installed windows cause drafts or allow condensation to develop.

If you’re not replacing windows as part of your remodel, you should buy energy-efficient storm windows for winter and also add weatherstripping and caulk around windows to air seal them. In the summer months, outdoor vegetation and awnings can protect your home from heat gain. So can shades, blinds and window films.

Window Stickers to Watch

To find energy-efficient windows and skylights, look for products with stickers from the National Fenestration Rating Council (NFRC). The NFRC measures the following key properties: U-factor, solar heat gain coefficient (SHGC), air leakage (AL) and visible light transmittance (VT).

  • U-factor indicates the rate of heat loss of the entire window. (It’s the opposite of R-value, which indicates the insulating value of the window). The lower the U-factor, the more energy efficient it is. Along with SHGC, this is the most important number to watch.
  • SHGC measures how much of the solar radiation that hits the window will enter the home. It is expressed as a number between 0 (0 percent) and 1 (100 percent). The lower the SHGC, the more radiation blocked by the window.
  • AL measures the cubic feet of air infiltrating a square foot of the window area. The lower the number, the less air can get in your house. Casement, awning and fixed windows tend to be tighter than sliding, single-hung and double-hung windows.
  • VT indicates how much visible light passes through the window. It is expressed as a number between 0 and 1. The higher it is, the more light is transmitted—this is good for day-lighting.
Filed under: Go Green