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Glossary of window efficiency terms to help when you shop


As you shop for windows, you’ll hear lot of jargon about glazing, spacers and cladding. You might be hoping to qualify for the new federal energy-efficiency tax credit, which requires low U-factors and solar heat gain coefficients.

Here is a glossary of window efficiency terms that might help you understand the gobbledygook:

Energy Star is a government label for energy-efficiency. If you buy qualified Energy Star windows before May 31, you can claim a federal tax credit on 30 percent of the cost of the window, minus installation, up to $1,500.

U-factor measures how well the window prevents heat from leaking from indoors to the outside. To qualify for the federal tax credit after June 1, a window must have a U-factor of no more than .30.

Solar heat gain coefficient measures how well a window blocks the hot sun from getting into your house. The lower the solar heat gain coefficient, the less solar heat the window lets in. In Arizona, solar heat gain coefficient is a bigger deal for windows than U-factor because it’s so hot here. After June 1, only windows with a solar heat gain coefficient of .30 or less will qualify for the federal tax credit.

Cladding refers to the window frame. A solid wood frame won’t hold up well under the Arizona sun. All-vinyl or all-aluminum frames never require painting, but vinyl can deteriorate in the sun, and aluminum absorbs so much heat that the inside of the frame gets as hot as the outside.

Glazing refers to the number of panes of glass the window has.

One-pane, single-glazed windows do little to keep the weather outside and the air-conditioned air inside. Double-glazed windows with a small air space between the panes are the smartest buy for Arizona homeowners. The air acts as an insulator to keep hot air out of the house and air-conditioned air in.

Double-hung or single-hung windows have top and bottom sections or “sashes.” Double-hung windows allow you to slide both the bottom sash and the top sash up and down, while single-windows have only one movable sash so just the bottom part moves.

Thickness of air space between the panes of glass in part determines the energy efficiency of double-glazed windows. A thin air space doesn’t insulate as well as a thick one. For maximum energy efficiency, look for windows with an air space of 5/8 of an inch.

Low-emissivity (or low-e) coatings are thin, transparent coatings of silver or tin oxide that allow light, but not heat, to pass through a window.

Tinted glass and tinted window films can prevent heat from wafting through your windows when it’s hot outside. But unless you want colored windows, there’s no need to pay extra for tinting.

Edge spacers hold the panes of glass apart and add an airtight seal to an insulated glass window.

Rosie Romero has been in the Arizona homebuilding and remodeling industry for 35 years. He has a radio program from 10 a.m. to noon Saturdays on KNST-AM (790). For more do-it-yourself tips and for Arizona’s most-trusted contractor referral network, go to rosieonthehouse.com or call (888) ROSIE-4-U during the show. The Rosie on the House column appears every Friday.


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