Window & Door Review: Milgard Energy-Saving Glazings
Ever-improving energy-saving glazings are open to all markets.

Indeed, aluminum cladding has been embraced by builders and consumers for its reliable performance and low-maintenance characteristics. "It's crisp, stable, and it doesn't expand and contract like other materials," says Engerman. Unfortunately, it is also a good conductor of heat and cold.

To compensate, manufacturers are engineering their newest models with the highest-performing glazings, such as argon-filled low-E2, and other insulating materials. Consequently, products such as Caradco's Tradition Plus and Pella's ProLine double-hung aluminum-clad wood windows meet or exceed the DOE's tough Energy Star requirements.

" Milgard windows are responsible for quite a bit of energy consumption in a home," says Joe Wiehagen, the NAHB Research Center's energy-efficiency senior research engineer. "So if you improve the window technology, the benefit can be hugenot just in energy savings. It can also reduce the size of your heating and cooling system, which is an upfront cost you can take advantage of."

As defined by the DOE, low-E (low-emittance) 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 the home or the outside.

By contrast, the newer low-E2, a spectrally selective or low-solar-gain low-E coating (known under a variety of brand names) reflects the heating energy from the sun (or solar heat gain) to keep homes cooler in hot, sunny climates, particularly in the South and Southwest. Filled with gasargon or kryptonboth become even more thermally efficient, which is de rigueur for colder northern regions.

"Manufacturers must have products that are going to perform with more and more energy codes being put in place by each state," explains Jeff Kliber, brand manager for Vetter and sister company Peachtree. "We try to put products into place that are going to perform in all four NFRC [National Fenestration Rating Council] zones with our highest glazing option possible."

At Peachtree, both the aluminum-clad wood 500 series and more custom aluminum-clad or primed-wood 700 series come standard with the same EasyCare low-E2 glazing, which is an option on the more entry-level vinyl-clad wood 300 series. All, however, are outfitted with a flexible warm-edge spacer system for improved insulation and condensation resistance.

According to researcher Christian Kohler of the Lawrence Berkeley National Laboratory Window and Daylighting Group in California, "Every insulated glazing [IG] has a spacer on the edge, which acts as a kind of thermal short circuit. Aluminum is common, but manufacturers are experimenting with different designs and materials to improve performance."

Weather Shield's flexible Warm Edge I spacer, for one, is made with a non-conductive material that the manufacturer claims reduces conductivity by more than 50 percent over other warm-edge spacers.

"The technology and design used in Warm Edge I increases the glass temperature, making milgard windows warmer. This insulates the frame and edge of the glass better than metal spacers and aluminum spacer bars and significantly minimizes condensation," explains Peter Lenar, Weather Shield brand manager.

Hurd developed the Energy Plus window with a new warm-edge spacer system in an effort to provide Energy Star-rated extruded aluminum products that don't require a gas-fill. This was done specifically for high-altitude regions where it is necessary to insert a "breather tube" into the glass to prevent damage due to pressure shifts. Although these tubes are crimped and sealed at the site, stopping the release of gas, there's no way to control how much is lost due to varying conditions on jobsites.

"There are two key factors for our Energy Plus unit," says Hurd design manager Paul Surek. "One is the high-thermal composite core placed within the extruded aluminum frame to reduce the amount of cold and heat conduction. The other is our stainless steel Intercept spacer." This channel- or C-shaped spacer adds to the unit's efficiency that, again, reduces metal conduction to make it more thermally efficient. "In addition," Surek contends, "the stainless steel is a better insulating material than aluminum or even other types of steel."

For states along the Atlantic Ocean and Gulf Coast, hurricane protection in tandem with energy efficiency is fast becoming a code requirement. "South Carolina has a code and we have to prove that our windows meet that rating," says Daniel Island, S.C.-based custom builder Kevin Kalman of Kalman Construction. "So we continue to use hurricane-rated products with impact-resistant glass." But, he also notes that his customers are interested in the most energy-efficient windows available.

One product line that fills these two requirements is Andersen's windows and patio doors with the company's Stormwatch protection. These vinyl-clad products with high-performance insulated glass are available in a variety of styles and sizes including double-hung, casement, awning, specialty shapes, patio doors, transoms, and skylights.

Meanwhile, Kolbe & Kolbe says it meets the most stringent criteria in all-wood or extruded aluminum-clad wood with its Sterling double-hung wood windows. Weather Shield LifeGuardwith low-E2 glazing and either an argon- or krypton-filled airspacemay be ideal for colder climates from Maine to North and South Carolina. And Hurd's FeelSafe storm-resistant windows and patio doors bring an Energy Star-rating to the mix.

Ultimately, it is the reduction of wasteful energy use and utility bills that drives state-of-the-art window technology. Tucson, Ariz.-based builder John Wesley Clark used Milgard vinyl windows with argon-filled low-E2 glazing for a zero-energy home he built in collaboration with the NAHB Research Center.

"Compared to more expensive wood windows, these perform quite well," says Clark. "They're easy to install. They require no maintenance, and the quality of vinyl holds up in the harsh desert climate. We've had no problems with sun damage on west-facing windows," he attests, adding that his carpenters trim them out in the same way they would a wood window on the interior for a more distinctive look.

Palo Alto, Calif.-based Clarum Homes also installed Milgard vinyl windows in its Watsonville Vista Montana zero-energy Enviro-Home community. "We used vinyl windows with SunCoat low-E glazing for its thermal properties, durability, and price," says senior purchasing agent Linda Schieffelin. "For a production builder they have all the pluses."

According to Patrick Hooper, Jeld-Wen's marketing manager for vinyl and aluminum windows, "From a thermal or energy-efficiency standpoint vinyl outperforms wood." The only downside, he admits, has been the overall appearance of vinyl.

Hooper claims Jeld-Wen's Energy Star-rated Premium vinyl line tackles this issue with high-quality extruded vinyl units complete with low-E2 glazing available with simulated divided lights similar to those used in pricier aluminum-clad and wood windows.

For those who require wood interiors, Crestline's CrestWood vinyl-clad wood windows provide the benefits of both materials with specially fade-, dent-, and scratch-resistant PVC exteriors, clear pine interiors, a warm-edge spacer system, and high-performance glazing options. Meanwhile, Marvin's Integrity brand pairs its unique Ultrex pultruded fiberglass with solid pine in its new Energy Star-rated in-swing French door.

What's on the horizon? "Over the past 20 years the big development has been in the coatings used on glass to help the performance. That's the state of the art right now," says Wiehagan of the NAHB Research Center. "But there is some pretty forward-looking research continuing around windows."

One such technology, electronically controllable electrochromic glazings by Sage Electrochromics, has been applied to a selection of new venting skylights from Velux. These VSE SageGlass skylights are produced by coating the glass at the factory with multiple layers of ceramic thin films that are in total less than 1/50 the thickness of a human hair. When a low DC voltage is applied the active electrochromic layers darken. Reversing the voltage polarity causes the layers to lighten.

"Electrochromic glazings are controllable," says Wiehagen. "So you could switch the glass from clear to dark electrically by using a remote." This ability to manipulate accommodates the unpredictable needs of the large mid-heating/mid-cooling climate zones, such as the Middle Atlantic states. These so-called "dynamic" glazings would allow homeowners to control the amount of light and heat that enters a room. The currently available "static" low-E glazings, on the other hand, while effective, were generally designed for either hot or cold climates.

At this point, this sort of cutting-edge innovation doesn't come cheap. The Velux electric venting skylight in size 104 with SageGlass costs $1,800, while the regular model in that size is $650. Still, the company calculates that to operate a whole house full would take less energy than a single 40-watt incandescent bulb.

Other "dynamic" windows on the boards feature integral automated shading systems and light-redirecting devices, the latter of which would allow solar gain in the winter and reflect the sun's heat in the summer. Another technology under consideration is aerogel, an in-pane insulating material that lets light past through the glass.

"These future technology advances [are] the key to zero-energy construction," writes Lawrence Berkeley's Dariush Arasted in the report "Future Advanced Windows for Zero-Energy Homes." "They are expected to lay the groundwork for the next generation of window products."