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Replacement Windows: Measure Thrice, Order Once

Scott Gibson, Contributing Editor

I would like to replace all my windows with more energy efficient units. Without removing the original frames, how and where should I measure for the proper installation?

Identify the dealer you're going to buy the windows from and decide whether you're going to install the replacements yourself or have an installer do the whole job. If you opt to turn the job over to a local window dealer, the measurements aren't your problem. All you have to do is write the check.

But if you plan on installing the windows yourself to save a few dollars, ask the dealer or window fabricator exactly what you should measure--and that can vary depending on what type of replacement window you buy and who you buy them from.

Frame-and-sash replacements are a good option when the window frame, trim, and siding are in good condition. New window sashes are contained in a frame that fits inside the existing jambs. You remove the old sash stops and sash, tip in the new frame, and screw it in place. It's a little more complicated than that, but not too much.

With these windows, you measure the width and height of the existing window, jamb to jamb, in several places and use the shortest of the dimensions. If there's a bow in the frame and you happen to get your measurements there, the new frame might not fit.

You also must make sure the window opening is square. To do that, measure the diagonals of the window opening from corner to corner. If those dimensions are the same, the window is square. If not, you have to compensate by using a smaller replacement frame and making up the difference with trim or expanders at the head and bottom of the window. If you need some more help, check out this article on how to measure windows for replacement.

Depending on the fabricator, the new windows could come in increments of ¼ in or ½ in. It's better to order a window frame that's a little too small rather than get one that won't quite go into the opening.

Understanding all of these details in advance is a good reason to choose a dealer or fabricator. Whoever you select should provide you with precise instructions on where and how to measure the existing window to make sure the new frame fits. Be specific on whether you want a new frame along with a sash or the sash only.

Energy efficient windows can cut heating and cooling bills substantially. You may end up saving more than if you let your cash just sit in a high interest savings account. To get the most out of your investment, order windows that are appropriate for your climate. The U.S. Department of Energy's Energy Star website at www.energystar.gov makes specific recommendations for different climate zones in the U.S.

Two key values are the window's "U-value" and the "Solar Heat Gain Co-efficient." U-value is a measure of how well the window blocks the passage of heat; the lower the number, the better an insulator the window is. The heat gain co-efficient tells you how much solar energy the window lets through; the lower the number the less heat transmittance.

Energy Star recommendations are different depending on where you live, so check that before making a purchase.

About the Author
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.

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