How to Fix a Foggy Window Between Panes

Foggy windows between panes indicate seal failure in double or triple-pane windows. You can either replace the glass unit or the entire window, as the seal cannot be effectively repaired.

1. Confirm Seal Failure First. Check if the fog is actually between the panes by cleaning both sides of the window thoroughly. If moisture remains visible after cleaning, the seal has failed and moisture is trapped between the glass layers.
2. Get Exact Measurements. Measure the width, height, and thickness of the insulated glass unit. You'll need these dimensions to order a replacement. Most units are 1/2 inch to 1 inch thick for double-pane windows.
3. Safely Extract Stops. Carefully pry off the interior window stops using a putty knife or pry bar. Work slowly to avoid cracking the wood. Number each piece so you can reinstall them in the correct order.
4. Lift Sash Carefully. Lift out the window sash containing the fogged glass unit. Have someone help you as glass units are heavy and awkward to handle. Set it on a padded surface to prevent damage.
5. Free the Old Unit. Remove the glazing compound or rubber gaskets holding the glass in place. Carefully lift out the failed insulated glass unit. Note how the glass sits in the frame for proper reinstallation.
6. Set New Glass. Place the new insulated glass unit into the sash frame exactly as the old one was positioned. Apply new glazing compound or install new gaskets to secure the glass firmly in place.
7. Test Operating Function. Place the sash back into the window frame, ensuring it operates smoothly. Test the window's opening and closing function before proceeding to the final step.
8. Restore Stop Trim. Nail the window stops back in place using finish nails. Use the numbers you wrote earlier to ensure correct placement. Fill nail holes with wood putty and touch up paint as needed.