Know the language of windows

It’s also helpful to familiarize yourself with terms that appear on many window labels:

Glazing is simply the glass used in the window. The number of layers of glazing (single, double, or triple) don’t necessarily equal greater efficiency; the presence or absence of the other items in this list affects a window’s total energy performance, says Petermann. Glazing coatings can substantially affect a window’s U-factor, or degree of insulation against the outdoors.

Low-E stands for low emissivity, the window’s ability to reflect rather than absorb heat when coated with a thin metallic substance. Low-E coatings add up to 10% to the price of a window.

If your windows are in relatively good shape but you’d like better insulation, you can buy and apply Low-E films to your windows. They’re effective, but not as much as those put between glazing layers during manufacture. Look for the NFRC rating on these films, Petermann says. Low-E films start at about 50 cents per square foot, but you may want to check into the cost of having them professionally installed for large or complicated applications.

Gas fills typically consist of argon or krypton gas sandwiched between glazing layers to improve insulation and slow heat transfer. They often won’t work at high altitudes because differences in air pressure cause them to leak out.

Spacers separate sheets of glass in a window to improve insulating quality; the design and material are important to prevent condensation and heat loss.

Frame materials include vinyl, wood, aluminum, fiberglass, and combinations of. They each have different strengths: Vinyl windows are good insulators and are easy to maintain, but contract and expand with temperature changes, affecting the window’s air leakage; wood offers a classic look but is similarly affected by moisture changes and needs regular maintenance; fiberglass is very stable and low-maintenance but can be expensive; and aluminum is lightweight, stable, and a good sound proofer but is a rapid conductor of heat, making it a drain on energy efficiency.

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