Between 25 to 50 percent of energy used in a home goes right out the window – literally. In most homes, windows provide the biggest openings between indoor and outdoor air, and the biggest opportunity for valuable energy to escape.

To assist homeowners with upgrading from old, drafty windows, the federal government is offering tax credits under a new act signed into law in late 2010. Available until Dec. 31, 2011, the tax credit is for up to 10 percent of the purchase price, excluding labor and materials for installation, and is capped at $200 for qualifying windows and skylights, and $500 for exterior doors.

Qualifying windows, doors and skylights must meet the Energy Star rating. According to Energy Star, installing windows, doors and skylights with the Energy Star label shrinks energy bills – and carbon footprints – by about 7 to 15 percent, compared to non-qualified products.

“Tax credits offer homeowners immediate savings, but the benefits of Energy Star rated windows are long lasting,” says Erin Johnson, window expert from Edgetech I.G. “Research shows that in cold climates, energy-efficient, dual-pane windows with low-e coatings can reduce heating bills by as much as 34 percent. In warm climates, they can cut cooling costs by 38 percent.”

Understanding Energy Star

While previous tax credits used a standard qualification for all states, the new tax credit is dictated by Energy Star requirements, which vary depending on four climate zones: Northern, North-Central, South-Central, Southern.

North and North-Central zones have stricter U-value requirements, which is the rate heat is lost through a window. In Southern and South-Central zones, the solar heat gain coefficient (SHGC) is more important because it signifies how well windows block the sun’s heat from warming the indoors and counteracting air conditioning.

“For both U-value and SHGC, the lower the number the better the performance,” Johnson says. “Requirements vary, so it is important to check Energy Star’s website to find windows that qualify in your zone. However, to ensure the best long-term value, you should really look at all factors that make up the window from the glass and framing to the spacer system.”

Window components that promote efficiency

True energy-efficient, sustainable windows hold such characteristics as low-conductivity gas fillings (argon or krypton), low-e coatings and nonconductive spacer systems that separate the glass panes. The spacer system is a key element to promoting sustainability in window systems because it provides the seal between the indoor and outdoor air. If that seal fails, condensation will occur and the gas filling will leak and no longer be effective.

“Nonconductive spacers, such as the Super Spacer warm edge spacer system, are known to provide a lasting seal, ensuring the window will retain its energy-efficient benefits for many years,” says Johnson.

The outside materials also play a role in efficiency and sustainability.

“Homeowners are better off looking for nonconductive components, framing and sashes,” Johnson says. “Wood, composite and fiberglass frames are time-tested and are proven to be the most sustainable and energy efficient, standing up to a wide range of temperatures, UV light and the deteriorating effects of condensation.”

Edgetech I.G., an Energy Star partner, is educating homeowners, legislators and companies worldwide on energy conservation and sustainable building practices. To learn more about choosing energy-efficient windows or federal tax credits visit www.sustainaview.com or www.energystar.gov.