DIY Replacement Windows

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Finding a Square

Installing a window yourself will only work when the replacement window is the same size and shape as the old one and when the existing window opening is square. To determine whether your window opening is square, measure it diagonally one way (from the upper left corner to the lower right corner) and then the other (from the upper right corner to the lower left corner). If the opening is square, the two measurements will be the same, give or take 1/8 inch. The slightest deviation from square can prevent the sash from closing and the weather stripping from sealing properly. If that happens, you'll be stuck with drafts, condensation, and high utility bills.