Choosing the Right Window: Energy-Efficient Windows and Frames

The right window is both energy efficient and beautiful to behold.


Andersen Windows' 400 series double-hung windows are Energy Star with a low-E coating.

Content Tools

Arguably your home’s most direct meeting place with the outdoors, windows let in daylight and allow for ventilation—while enhancing the ambiance of your living space. Unfortunately, poor-quality or aging windows can be a liability, making your home susceptible to sweltering summer sun and chilly winter drafts.

Windows can be responsible for losing 15 to 30 percent of a home’s total heating load and more than 50 percent of its cooling load, depending on their material, size and placement. Uninsulated windows that fit poorly or are damaged may contribute even more to energy loss. Understanding window components—including glass and frame types—can help you make a wise, long-term investment.

Got glass?

Glass is a relatively benign, recyclable material made from silicon dioxide (sand).  The simplest way to improve a window’s efficiency is to choose multiple layers of glass (called “glazing” in the window industry). You can choose from double-, triple- and even quadruple-glazed options.

In addition, most window manufacturers inject gas between the sheets of glass to help improve the window’s insulating properties. Argon, krypton or carbon dioxide—all nontoxic, odorless gases—have significantly lower heat transference than air. Unlike past double-glazed versions that developed a haze, today’s quality windows are sealed well, and many carry warranties against such defects.

Lightly tinted glass reduces heat gain in hot climates, and the newest types offer better visibility and color perception. Even more effective are low-emissivity (low-E) coatings such as silver oxide, which reduce ultraviolet light penetration but let in as much as 95 percent of the visible light. Low-E coatings protect furniture from fading, and they control heat loss by reflecting infrared energy (warmth) back inside.

The great frame-up

When choosing window sashes and frames, energy efficiency should be the first priority, but also consider the material’s sustainability and effect on human health. 

Traditional  wood-framed  windows are solid and made from a natural, renewable material. They resist condensation when used with double or triple glazing. High-quality wood windows can last a century or more, but only if regularly maintained with finishes or paints. (Low-VOC coatings don’t outgas as many toxic chemicals.) To ensure that the wood has come from sustainably managed forests, find a frame that’s certified by the Forest Stewardship Council (FSC). The number of manufacturers that use FSC wood is limited but growing; visit for sources.

Fiberglass windows, common in commercial buildings but rare in homes, have ecological pros and cons. Fiberglass is made from glass, but the manufacturing process is more energy intensive and the end product isn’t easily recycled. On the other hand, fiberglass is stronger and more insulating than solid wood. It’s also more expensive.

Although aluminum and steel frames are inexpensive and potentially recyclable, they’re mediocre choices for an energy-efficient home. Both are poor insulators and encourage condensation.

The worst option for an eco-friendly home is vinyl (polyvinyl chloride, or PVC). Although PVC-vinyl is relatively inexpensive and has better insulative properties than metal, it’s a known carcinogen that’s linked to human illness and environmental mayhem. When vinyl is burned or incinerated, it gives off toxic dioxins that accumulate in human tissue and the environment. Although unplasticized PVC (abbreviated as uPVC) and PVC-free windows have been introduced, these plastics still rely upon energy-intensive manufacturing and petroleum byproducts.

Composite windows—a combination of vinyl, wood, metal or even recycled plastic—are becoming common. Some companies put wood on the window’s interior side so it can be painted to match the décor, but they use vinyl on the outside. Others put vinyl cladding over solid wood. Even so-called solid-wood windows may contain glazing spacers or tracks made from another material.

Other energy-saving options

Salvaged windows are economical and available in many construction exchanges and reuse shops. Avoid buying older windows (pre-1970s) that might be less energy efficient or covered with lead paint.

If your budget won’t cover whole-house replacement of single-glazed windows, consider storm windows. They’re not as insulating as replacements, but they do improve energy efficiency. In addition, window coverings such as insulating blinds or shutters help regulate temperatures.

And here’s good news: There’s currently a tax break for homeowners who replace their windows with more energy-efficient models by December 31, 2007. Check the Department of Energy website for details:

A Cleaner Look: Window Frames

Solid wood

Pros: Insulates well, can paint to match décor
Cons: Will rot without regular paint or finish
Cost: $$$

Solid Vinyl

Pros: Won't scratch, cleans easily
Cons: Health and environmental toxin
Cost: $ to $$


Pros: Durable, recycles easily, inexpensive, won't rust
Cons: Attracts condensation, insulates poorly
Cost: $


Pros: Strong enough for very large windows, recyclable
Cons: Attracts condensation, insulates poorly
Cost: $$ to $$$


Pros: Durable, made from glass
Cons: Not easily recyclable
Cost: $$$


Pros: Can be very energy efficient (depends on model)
Cons: May include vinyl components
Cost: $$ to $$$


wood windows

Efficient Windows Collaborative
standards and labeling

Energy Star
efficiency standards

Integrity Windows from Marvin
fiberglass windows

J. S. Benson Woodworking & Design
FSC-certified wood windows

FSC-certified wood windows

fiberglass-clad wood windows

National Fenestration Rating Council
window ratings

wood windows

Weather Shield
wood windows