High-Performance Windows: Page 3 of 3

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Triple-pane unit from Optiwin
Modern high-performance windows—like this triple-pane unit from Optiwin that achieved the German Passivhaus certification— combine excellent sealing, thermal breaks in the frame, and specialized coatings.
High-tech windows are an integral part of an efficient building envelope
High-tech windows are an integral part of an efficient building envelope, with casings and glazings working with other architectural features to improve building performance.
ntus Windows’ Eforte aluminum- and wood-framed window combines interior aesthetics and exterior durability.
Triple glazing provides some of the lowest window U-factors, but frame features affect overall performance, too. Intus Windows’ Eforte aluminum- and wood-framed window combines interior aesthetics and exterior durability for excellent efficiency.
SeriousWindows’ suspended-film technology matches or exceeds the performance of triple-glazed windows.
SeriousWindows’ suspended-film technology matches or exceeds the performance of triple-glazed windows, while minimizing weight and cost.
Casement windows capture the most air for ventilation when opened and seal tighter than other types of operable windows.
Casement windows capture the most air for ventilation when opened and seal tighter than other types of operable windows.
Modern, high-tech vinyl-framed windows like this one from SeriousWindows offer good thermal performance, low maintenance, and longevity.
Modern, high-tech vinyl-framed windows like this one from SeriousWindows offer good thermal performance, low maintenance, and longevity—at a lower cost than other frame materials.
High-performance window by Unilux from Germany
In the past, high-performance windows (like this Unilux from Germany) were difficult to get stateside. Today, these types of windows are more readily available through U.S. distributors.
Triple-pane unit from Optiwin
High-tech windows are an integral part of an efficient building envelope
ntus Windows’ Eforte aluminum- and wood-framed window combines interior aesthetics and exterior durability.
SeriousWindows’ suspended-film technology matches or exceeds the performance of triple-glazed windows.
Casement windows capture the most air for ventilation when opened and seal tighter than other types of operable windows.
Modern, high-tech vinyl-framed windows like this one from SeriousWindows offer good thermal performance, low maintenance, and longevity.
High-performance window by Unilux from Germany

Probably the best windows for passive solar gain come from Germany, where building codes require higher-performance techniques than in the United States, and where the Passivhaus movement—which focuses on eliminating mechanical heating and cooling systems—is strong. Some reputable manufacturers are Internorm, Optiwin, Pazen EnerSign, and Unilux. These manufacturers offer triple-pane windows with U-factors in the 0.10 to 0.15 range combined with SHGC above 0.50. These units are expensive, however, at upwards of $100 per square foot of window space (not including shipping). What is available depends on what dealers are nearby. Remember that you only need low U-value, high SHGC windows for the south side of your home if you are building a passive solar home, so it may make sense to use a combination of windows from different manufacturers to keep costs reasonable. German manufacturers benefit from having ready access to low-iron glass (almost all iron oxide has been removed for clarity), developed primarily for that country’s booming PV market.

North American windows can be half the price of European ones, and shipping and lead times are substantially reduced, although design, operation, and energy efficiency are generally reported to be a notch below their German counterparts, according to NFRC certifications. There are dozens of window manufacturers, so a comprehensive review isn’t within the scope of this article. Accurate Dorwin, Duxton, Fibertech, Inline Fiberglass, and SeriousWindows are reputable North American manufacturers. U-values typically range from 0.15 to 0.30 for higher-quality windows.

So, where to begin? If you’re interested in highly energy-efficient windows, you probably won’t find them at your big-box hardware store, although acquainting yourself with the prices of average windows will give you a starting point. The best place to start is the Window Selection Tool on the Energy Efficient Windows Collaborative website. This is a location-specific tool that will generate a window availability list based on criteria such as triple-pane or a high SHGC. Your window purchase can rival buying a car in cost and complexity, and the more legwork you do for your specific project and location, the better off you’ll be.

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Stephen Hren is a builder and writer. He is the author of Tales from the Sustainable Underground and coauthor of A Solar Buyer’s Guide for the Home and Office (see www.earthonaut.net).

Energy Efficient Windows Collaborative • efficientwindows.org • Window industry info

Passivhaus windows • bit.ly/HPwindows • Sourcing low U-value, high SHGC windows

National Fenestration Rating Council • nfrc.org • List of window manufacturers

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