Green Homes Special Series: Part Eight: Windows

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Today’s advanced materials, better science and new manufacturing processes make for high-performance window units. Those building new or wanting to replace inefficient windows with improved units have a lot of information to digest. Window Components U.S. Green Building Council spokeswoman Lauren Connelly says a window’s performance is determined by three parts: the glazing, the sash and the spacer system. Measuring performance means looking at such factors as how the window conducts heat and transmits light. Follow a few simple steps to increase your windows' energy efficiency. 1. Look for an Energy Star label. Energy Star is a joint program of the U.S. Environmental Protection Agency and Department of Energy (DOE). Its label confirms a window's energy efficiency based on its impact on heat gain and loss in cold weather and heat gain in warm weather for a given climate zone. The labels pertain to four climate zones: Northern—mostly heating; North/Central—heating and cooling; South/Central—cooling and heating; and Southern—mostly cooling. 2. Review the label from the National Fenestration Ratings Council (NFRC). The NFRC is an independent organization that rates and certifies energy performance in all windows. Its label lists several performance rankings. Understanding the ratings is key to making the right choice. The NFRC label contains a lot of information about a window’s energy performance. Photo courtesy of NFRC. NFRC Executive Director Jim Benney says, “It is important for consumers to understand the impact that windows have on their energy bills. By choosing the right windows for their climate, homeowners can save more than 30 percent on their annual energy costs. “The two most important measurements are the U-factor, which indicates the rate of heat lost through a window, and solar heat gain coefficient, which measures how well a product blocks heat caused by sunlight.” For example, he says dual-paned windows with low-e coatings are typically 20 to 25 percent better than uncoated dual-pane windows. Using gas-filling and warm edge spacers (low-conductance spacers to reduce heat transfer near the edge of insulated glazing) along with the top-of-the-line low-e coatings can reduce U-factors to 0.30, a 40 percent improvement.

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