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 www.FSCUS.org for sources.