How to Replace Glass Thermal Windows

The presence of thermal windows increases the energy efficiency of your home, with each multiple-paned window sash adding a bit more insulation. This only works however, when the windows are whole and set well within the frames of the window sashes. You can replace the glass pane in a damaged thermal window by pulling out the old one and inserting the new one. One of three methods is used to hold the glass in place: rubber gasket, adhesive tape or caulk. Each requires a slightly different method of replacement, but each technique can be accomplished by a do-it-yourself homeowner.

Step 1

Remove the window sash containing the damaged thermal windowpane from the window frame. Follow the window manufacturer's instructions, because removal methods vary by brand. Place the sash on a flat work surface.

Step 2

Examine the window sash to determine the method used to seal the glass into the frame. Gasket-sealed windows have a rubber gasket surrounding the window in a screwed-together frame. Adhesive-sealed windows have vinyl, wood or aluminum strips along the edge of the windowpane that hold it in place on the frame, using adhesive tape. Caulk-sealed windows typically are wooden and use wood strips glued into place with caulk to hold the windowpane in the frame.

Step 3

Disassemble a gasket-sealed window sash by removing two screws located at opposite corners of the sash. Leave the other two corners joined to maintain the shape of the window frame during the replacement process. Pull the frame apart carefully, tapping gently at the frame pieces with a rubber mallet to pry the corners apart and get to the windowpane. Take the glass from the pane and remove the rubber gasket.

Step 4

Take apart an adhesive-sealed window sash by removing the adhesive-taped strips using a putty knife. Pry the strips away from the frame by placing the edge of the knife between the frame and the strips where the adhesive tape secures the pieces together. Pull the pane from the frame once you remove the strips.

Step 5

Dismantle a caulk-sealed window sash by prying up the caulked-in-place wooden strips, using a putty knife. If the installer stapled the wooden strips into place, they may crack as you remove them. Glue the cracked strips together with wood glue for reuse in the frame. Remove the glass from the frame once you’ve removed the wood strips.

Step 6

Measure the glass pane with a measuring tape to determine its exact dimensions, so you can obtain the correct replacement size. Make sure the new windowpane is an exact size match.

Step 7

Place the new thermal glass pane into the window sash frame and secure it using the appropriate method for your window.

Install the rubber gasket around the edge of the pane, then reassemble the sash frame around it, securing the frame with the frame screws.

For an adhesive-mounted pane, stick double-sided adhesive tape along the inside edge of the frame where the glass sits. Remove the protective paper from the other side of the tape and lower the pane into the frame, pressing it into place against the tape. Replace the stops that you pried away during the disassembly process.

For a caulk-sealed window, squeeze caulk onto the back strip on the frame where the glass will sit. Place the glass into the frame, onto the caulk. Lay a second line of caulk on the edge of the pane. Place the pried-off strips onto the pane edge, against the edge of the sash frame. Staple the strips back in place, taking care to staple into the side of the frame and not into the glass pane.

Step 8

Replace the sash in the window frame.


  • Wear work gloves during the replacement process to protect your hands in case of broken glass.
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