There was a time when the measure of a window was its ability to fit the architectural style of a house. That is still important today, but other factors now carry as much weight.
Simply put, the window is an integral part of the building envelope. Thus, along with the roof and walls, it’s part of the first line of defense against moisture, air, sound, and—most important for energy efficiency—heat gain and loss.
“The high prices for natural gas, electricity, and home heating fuel that followed the first oil embargo in the early 1970s made energy a high profile, pocketbook issue,” says the National Fenestration Rating Council (NFRC), a nonprofit organization that provides information about the energy performance of windows. “Many consumers became aware of R-values—a measurement of a product’s resistance to heat loss—and learned that materials (floors, walls, and roofs) with higher R-values are more energy efficient.”
Energy awareness may have started in the ’70s, but it has escalated in recent years with growing concerns about rising energy prices. “And this has affected windows. The state of affairs in the glazing market has changed quite a bit in the past few years,” says Brian Hedlund, product marketing manager for windows at Klamath Falls, Ore.–based Jeld-Wen. “Green [building] is tremendously important, and energy efficiency is a big deal.”
The average energy-efficient window uses a standard glazing package that includes low-E insulated glass, and it is more energy efficient than windows from 15 or even five years ago. But in conjunction with their glass-producing partners, window manufacturers are now able to offer glazing that increases energy efficiency or addresses specific situations.
Home buyers in different regions, for example, have different needs. In the North, a window’s U-factor, which measures how well a window prevents heat from escaping, is important. Buyers in warmer states, on the other hand, should be concerned with the solar heat gain coefficient, which measures how well a window blocks heat from the sun. And in the central regions, a window must do both. “There is no one option that is ideal for every climate,” says Tom Sinning, director of dealer sales for Warroad, Minn.–based Marvin Windows and Doors.
Because buyers and climates have different requirements, manufacturers have come up with ways to meet them. For example, Jeld-Wen says its high-performance low-E insulating glass is a good general purpose glazing because it “helps homes stay cooler in the summer and warmer in the winter.” But for warm regions, it offers LoE³-366.
“This glass features three transparent, microscopic layers of silver placed between layers of anti-reflective metal oxide coatings,” the company explains. The coatings block UV rays and reduce window heat gain.
Medford, Wis.–based Weather Shield Windows and Doors claims its Zo-e-shield is the world’s best energy-efficient glass, offering the lowest center-of-glass U-factors and solar heat gain coefficients. The line uses a combination of components such as warm-edge spacers, gas-filled airspaces, and laminated interlayers to fill various types of performance needs.
Earlier this year, Bayport, Minn.–based Andersen expanded its glazing options with SmartSun. Unlike standard solar glazing, SmartSun has an additional layer of silver that controls the amount of infrared energy transmitted, the company says.