How to Replace Single-Pane Glass Inserts With Dual-Pane Glass

Measure the jamb-to-jamb width of your existing window. Record the measurement. Measure the sash opening height. To measure, open the lower sash. Place the base of your tape measure at the point where the exterior side of the lower sash meets the window sill. Extend your tape measure up through the lower sash to the jamb at the top of the window. Record the measurement.

Measure the window sill angle. Place the sill angle finder on the window sill and rotate the inner wheel until the bubble is level. Record the angle reading on the device’s dial. You will need the width, opening height and sill angle measurements to order your double-pane sash insert kit.

Remove the old single-pane window sash inserts. To do this, score the interior side window stops from top to bottom on both side of the window. Gently pry up the interior side stops with the hammer and pry bar. Work carefully to prevent damage to the side stops if you intend to reuse them. Lift out the old single-pane lower sash and discard it.

Pry up the sash-parting stop from both sides and the top of the window and discard. Pull down the old single-pane upper sash, lift it out of the window and discard it. If your old window used pulleys and weights for sash balance, cut the pulley ropes before removing the sashes. Remove and discard the sash pulleys and sash weights.

Pack the sash weight cavities with insulation. Install the sash kit’s jamb liners on both sides of the window according to the manufacturer’s directions. In most windows, the jamb liners are nailed or clipped into place.

Insert the new upper double-pane window sash into the exterior jamb track and seat it firmly into place. Install the new sash-parting stops on both sides and the top of the window. Push the upper sash all the way to the top. Insert the new lower double-pane window sash into the interior jamb track, close it firmly against the sill and close the window lock.

Replace the original side stops, securing them with finishing nails. If the original stops cannot be reused, replace them with new side stops to fit your window. Secure the side stops with finishing nails. Set the nails below the surface with the nail punch. Fill the holes with putty. Paint the window trim if necessary.