Windows & Doors Review: Peak PerformaceHigh-tech window glazings reduce energy costs and keep houses more comfortable.

Joseph Strama couldn't believe his eyes. His company, Woodland Logcrafters in Medford, Wis., was installing drywall on a stick-built house in 20-degree weather. The source of his surprise? Completely dry windows.

Normally, with so much heat and humidity from the drywall process, the windows would be dripping with condensation or even frost in the cold weather. But the Weather Shield windows he had installed, which feature the manufacturer's Zo-e-shield high-performance glazing with a gas-filled air space and low-conductive spacers, were nearly room temperature. "During the process, [the interior of the] windows was never wet," Strama says. "I was totally amazed."

Chalk up another convert to the newest generation of high-performance window glass. It's been decades since the introduction of insulated glass units and transparent low-emissivity (low-E) coatings, and window and glass manufacturers continue to improve the energy efficiency of their products while lowering the prices.

"Low-E coatings have gone from an upgrade product to where it is almost standard now," says David Koester, brand manager at Weather Shield. "Consumers know they should have low-E glass." In fact, a market study from the American Architectural Manufacturers Association (AAMA) and the Window and Window and Door Manufacturers Association (WDMA) found that low-E use in the residential market stands at about 56 percent as compared to clear, tinted, and reflective glasses, up from 51 percent two years prior. That number is actually closer to 70 percent for non-aluminum windows, according to Jeff Lowinski, vice president of technical services for the WDMA.

A lot of those low-E windows are being speced for retrofit applications, Koester says, where they are replacing windows that could be up to 25 or 50 years old. But with energy prices on the rise and green building a full-fledged trend, new-home buyers are asking for high-performance glazings as well.

"They're thinking about the cost of heating 4,000-, 5,000-, 10,000-square-foot homes," says Roger Widing, owner of Widing Custom Homes in Traverse City, Mich., which builds large, high-end homes. To upgrade from standard low-E glass to a glazing package with a gas fill and low-conductive spacers, "it's 3 or 4 percent more to do it, but in the long run it's worth it," he says.

SUPER WINDOWS
Window manufacturers are packing the most technology into what Alex Wilson, president of GreenSpec Directory publisher BuildingGreen, calls "super-high-performance windows." These top-of-the-line windows start with three panes of glass with multiple gas-filled insulating spaces. The units are filled with argon or krypton gas because it's heavier and denser than air, so it slows down the convection current in the window. Krypton performs better and has been coming closer in price to argon, Wilson says, but krypton should only be used in small air spaces — less than 1/2 inch between panes.

High-performance windows also have several low-E coatings applied to one or more of the glass surfaces facing the air space between the panes. The transparent silver coating is attached to the interior and/or exterior pane depending on climate.

The latest generation of window glass, like Cardinal's LoE3-366 and PPG's Solarban 70XL, feature three low-E coatings to further improve the window's solar-heat-gain-blocking properties. Perhaps most impressive, however, is that unlike previous generations, the new glass improves the window's visible light transmission. "It reduces the SHGC [solar heat gain coefficient], and it's only slightly darker in terms of a tint," says Brian Hedlund, a product marketing manager for Jeld-Wen, which began offering the 366 glass in March.

Extra-efficient windows also can offer savings elsewhere, Wilson points out. "If you go to the extent of designing a super-high-performance building envelope, you can often really downsize your heating and cooling system," he says. "You spend more on the envelope but reduce the cost of the mechanical equipment."

DIRECTIONAL CHALLENGE
To achieve optimal efficiency, windows should be speced depending on their location in the house and the customer's individual climate. Gary Lee, sales manager for California Energy Consultant Service, a window dealer and installer in Rancho Cordova, Calif., says the setting sun in the hot summer months in his area bakes the west side of an already-warm home. "One guy said, 'I've got three windows on the west side. Can we change the glass in just those three windows?'" Lee says. Even though the customer already had new low-E windows, "it's worth the money for them to upgrade even after the fact."

In fact, he says at least half of his customers upgrade their windows for comfort reasons, rather than energy efficiency. "They say, 'Now we can sit at that table with the window behind it,'" he says. "You don't feel the heat or the cold."

Other clients are excited about protecting the interior of their homes from the damaging effects of sunlight. While laminated glass has always been able to block 99.9 percent of UV light, new high-end low-E glass can block up to 95 percent or more of UV light, reducing fading of carpet, draperies, upholstery, and artwork.

An added bonus of high-tech windows: Northern builders have discovered that high-efficiency window glazings allow their customers to keep the humidity at a more comfortable level without having to wipe the window sills for frost and condensation. "Even at 25 to 32 degrees, there was virtually no moisture on the windows," Strama says.