SEE CLEARLY: Different climates will call for different window options after the Department of Energy tightens Energy Star criteria. Left, Marvin's Ultimate Casement window comes with low-E coating options for different U.S. regions. Right, Andersen's latest offering, the 100 series, is made specifically for Western U.S. inhabitants.

SEE CLEARLY: Different climates will call for different window options after the Department of Energy tightens Energy Star criteria. Left, Marvin's Ultimate Casement window comes with low-E coating options for different U.S. regions. Right, Andersen's latest offering, the 100 series, is made specifically for Western U.S. inhabitants.

Important updates in the window world depend on location, location, location.

The Department of Energy (DOE) is changing Energy Star criteria for windows by remapping climate zones and tightening requirements by region. The Energy Star label was designed to help consumers recognize efficient products. But, today, too many windows meet the requirements, and some regions have even stricter codes than Energy Star, the DOE says.

"Energy Star needed to tighten criteria in order to remain the distinction for 'best-in-class' energy efficiency and to continue driving the production of more efficient products," DOE spokesperson Chris Kielich said in an e-mail.

In response, manufacturers are highlighting energy efficient packages that let customers choose the right options for their areas, and developing products for specific regions.

No numbers are final yet because the criteria are in the draft phase. But the DOE and manufacturers have a pretty good idea of where the criteria are headed. The criteria will take effect by Sept. 1, 2009, at the earliest.

Before understanding the changes, a dealer must grasp two things: U-factor and solar heat gain coefficient (SHGC). U-factor shows how much temperature transfers through a window, whether winter air against a window makes a room cold or summer heat increases air-conditioning bills. The lower the U-factor, the more insulation a window provides. SHGC measures how well a window blocks heat from sunlight. The lower the coefficient, the less heat from sunlight a window lets into a home.

In the heating-dominated North, criteria will require windows to meet a minimum annual energy performance, ensuring cold temperatures don't transfer through windows and sunlight can help heat a home. This means windows must have either a moderate U-factor with a moderate or high SHGC, or a low U-factor to compensate for a low SHGC. Windows with moderate U-factors and low SHGC will no longer make the cut.

A low U-factor will generate the most savings in the central United States, Kielich says. The South experiences many sunny, sweltering days, so low U-factor and low SHGC will help keep homes cooler there, she says. Energy Star's new criteria will require lower U-factors and SHGC in both areas.

The Pacific Northwest will get a separate zone because the area has more stringent building codes. Windows there will need to have lower U-factors.

The changes will roll out in two phases. Most manufacturers can meet the first phase without a major product redesign, according to the DOE. During the second phase, manufacturers may have to move past simply having low-E coatings to using inert gasses instead of air to fill the gaps between window glass, and companies may need to make triple-pane windows instead of double pane.

Some manufacturers are preparing for the first phase by letting consumers choose the properties they want their windows to have. Marvin's new window, the Ultimate Casement, includes argon gas to provide lower U-factors. The window is offered with a two- or three-coat low-E system to provide either a moderate SHGC, for places in the North, or a low SHGC, for the South. Milgard offers its new 3D and 3D Max energy packages that let builders customize packages to specific regions. Simonton also offers different options for different markets.

Other manufacturers are developing products for specific regions of the country. Andersen's latest window, the 100 series, specifically designed for the West, will roll out through the region in 2009. The company also offers SmartSun glazing that lets light, but not heat, transmit through windows. That glazing is most popular in the South.

"The days [of offering] one glass package nationwide are gone," says Christopher Burk, product manager with Simonton.

–Victoria Markovitz