Removing old windows and installing new ones as a DIY project will only work when the new one is the same size and shape as the old one and the existing one is square. To determine if your window opening is square, measure 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. You’ll be stuck with drafts, condensation, and high utility bills if that happens. Next, score head stop and gently pull it loose with pliers. Set aside for later use. If you wish to remove the surrounding trim, use a utility knife to slice through any paint or caulk between the interior casing and the wall. Use a flat pry bar and a scrap piece of wood to remove the casing. If you’ll reuse the casing, use slip-joint pliers to remove the screws. Tip: After removing a stop or other trim pieces, use pliers to pull the nails through the back of the piece. Doing so reduces the odds that it will split or fracture. Fold the jamb liner at a 90-degree angle underneath the sash. Repeat with the upper sash, folding the jamb liner across the top of the sash. Attach the jamb liners to the liner brackets. Each liner should pop into place. Reattach the inside stops. Set the nails and fill the holes with wood putty. Caulk the seams and touch up with paint. Removing Old Windows from the Exterior A metal or vinyl window may have a flange nailed to the sheathing and covered with siding; in that case, you must cut back the siding. Molding that rests on top of the siding is the easiest to remove.
