Before you order the replacement sash kit, you'll need to measure the existing sash opening. Begin by measuring the width of the opening in the old window from jamb to jamb. Then, measure the sash opening height. Open the bottom sash and place a piece of scrap lumber in the opening to hold the window up and run the tape measure up the inside of the frame to the head jamb (Image 1) and down to the point where the exterior side of the sash meets the sill (Image 2). You can usually identify the bottom point by the existing paint mark.
The new kit should include jamb tracks, a pair of sashes, mounting clips, a parting stop and complete set of directions (Image 1). The steps shown in this project were for the particular sash-replacement kit shown. Individual steps may vary somewhat for different models, so read any instructions that included with the window kit you select.
Once you've received your kit and are ready to remove the old sash, begin with the window stops. Using a utility knife, score the side-stop all the way down the length of the window from top to bottom. Gently pry the old side stop off using the pry bar (Image 2). The stops can be reused or replaced with new ones -- if you intend to reuse the old ones, take care in removing them so they don't get damaged.
Then, remove the sash-parting stop. Since this area will later be covered by the new insert, you can break these pieces out with a pry bar (Image 3). After removing all of the old sash-parting stops, remove the upper sash by sliding it down and lifting it out (Image 4). If your window has a pulley system, you'll need to cut the pulley rope before removing the sash.
Finally, remove the the pulleys and weights from the window-frame cavity (Image 5).
Fill the empty cavity with insulation (Image 1); then nail the metal brackets, spaced evenly, down both sides of the window (Image 2). Start about 2" from the top and finish about 2" from the bottom.
Snap the vinyl jamb liners onto the brackets on the side of the window frame. Start at the top and use your hand to pound the liners into place (Image 1). When installing the jamb liner, make sure that the blind stop leaf (Image 2) is not folded under the jamb liner. This will ensure a tight seal over the blind stop.
Use small finishing nails to install the new stop-strip at the top of the frame (Image 3). Nail the strip in place with the weatherstripping facing outward.
Pull down and lock the metal clutches in the jamb liners with a screwdriver (Image 1). Place the top sash into the exterior track and ease it into place , lowering it into the clutches (Image 2). Swing the sash up until the top locks into the side-track. With the top sash in its tracks, it's safe to slide the sash up (Image 3).
The lower sash installs in the interior track in the same way. Once it's in the track, swing it up until it locks into place (Image 1). With the lower sash seated firmly in the track, slide it all the way down and set the lock (Image 2).