Energy Star

Conserve energy.

Besides improving the value and comfort of your home, installing new windows can be the most significant energy-efficient upgrade available. There are many factors to consider when replacing the windows in your home with energy-efficiency in mind.

Low-E and Low-E2 glass is now an industry standard. A window that does not have Low-E glass will have significantly higher thermal penetration, enough to feel a difference while inside near the window.

Double-paned windows are also commonplace. Major factors contributing to energy-efficiency are the thickness of the glass and the airspace between the glass panels. This airspace can optionally contain Argon gas. It's important to note that Argon gas will dissipate at a rate of approximately 10% per year. On the interior side of the insulated unit, a protective film is applied that helps with the reflective qualities of the glass, which in turn, prevents the fading of interior furnishings.

The most energy-efficient window frame is wood because of its natural insulation factors. Vinyl, fiberglass, and aluminum clad windows are wood-framed with a vinyl, fiberglass, or aluminum "wrapper", which can balance maintenance and insulating factors. Since the weather here in the Bay Area is fairly mild, vinyl and fiberglass frames are a popular practical choice since they are more resilient to oxidation and rust.

Be sure to check out the Efficient Windows Collaborative for detailed information.