Wonder Glass: Energy-efficient low-E glazing has many benefits, but for a price.
When low-emittance window glazings first appeared in the 1980s, many builders and remodelers were hesitant to use them.
Faced with costs of $40 to $50 per window more than clear glass, Dale Dornburg, president of Webster, Wis.-based A New Look in Construction, says he and other pros questioned whether the expense was worthwhile.
“Everyone's pretty skeptical when something comes out on the market,” Dornburg says. “It's like … is it worth the money?”
Twenty years later, about 50 percent of all residential glass is low-E, with that number increasing each year, says Dariush Arasteh, a deputy group leader with the Windows and Daylighting Group at federally funded Lawrence Berkeley National Laboratory in California.
Many manufacturers now offer low-E as standard. And even though they still cost more, pros like Dornburg are buying.
As defined by the U.S. Department of Energy, low-E coatings are highly reflective, transparent coatings applied to the window glazing. Because they are designed to reflect long-wavelength infrared radiation, less heat is transferred through the window, either from inside or outside the home.
Work on low-E glass began in 1976, when the federal government issued several grants through Lawrence Berkeley to a series of small firms tasked with researching potential methods for applying low-E films. Southwall Technologies developed the technology, and by 1980, was working closely with several major window manufacturers.
In 1983, Cardinal IG began applying a soft coat of low-E to the glass it provided Andersen, creating pressure for others to follow suit. By 1985, 5 percent of the market was low-E, according to industry reports.
Early low-E coatings were designed primarily for colder climates, where heat loss is a problem. But by the early 1990s, the government and manufacturers developed “spectrally selective” coatings that also admit daylight but block the transmission of ultraviolet and infrared heat.
These newer low-solar-gain double low-E coatings reflect the heating energy from the sun to keep homes cooler in hot, sunny climates. When filled with argon or krypton gas, the product is even more thermally efficient, manufacturers claim.
Steve Beetch, vice president of Schmidt Siding & Windows in Mankato, Minn., says the advances have improved appearances. Early low-E glazings were prone to scratches and had a blue, gray, or bronze tint, but today's coatings often are not visible, Beetch claims.
Pros cited a number of advantages to the product, including the prevention of floor and upholstery fading, increased flexibility in the placement of HVAC systems, environmental friendliness, and reduced heating and air-conditioning costs.
“I don't think there's a downside other than they may cost more than a typical window,” says Joe Wiehagan, senior research engineer with the NAHB Research Center in Upper Marlboro, Md.
Ed Cook, president of Historic Traditions, says he uses low-E windows to attract buyers to the high-end speculative homes built by his Fort Worth, Texas-based company.
“It's still a marketing tool somewhat for me,” Cook says. “If I can walk a potential buyer through a house and explain to them that on the southwest exposure we've gone to the expense of installing low-E … it helps sell the house.”
