How to Defog a Thermal Pane Window

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Defog a thermal pane window for maximum window performance.

Thermal pane windows are the industry standard for new home construction, and many older home have existing windows updated to thermal pane. Thermal pane windows have two panes of glass and provide more insulation than regular windows. Occasionally, these double pane windows fog up between the panes. Excessive moisture in the home, clogged breather holes and improperly sealed windows can fog. Defogging these windows comes with proper window maintenance.

Windows with Breather Holes

Step 1

Remove the interior pane of glass from your windows. Locate the locking clips on the sides, top and bottom of your windows and put into the unlock position. Pop the interior pane of glass out and set it aside. You may need to use a flat-head screwdriver to gently dislodge the pane before removing.

Step 2

Wipe off any moisture from the remaining pain of glass. Use a hairdryer to make sure the corners and seams are free from moisture. Repeat this step with the interior portion of the window.

Step 3

Clean the breather holes located at the top right and left of the inside of the window. These look like small slits in the wood or other material your windows are made of. For stubborn debris lodged in the holes, try a can of compressed air to dislodge and remove with the vacuum.

Step 4

Leave the interior pane of glass off the window for at least an hour to allow for thorough drying. When completely dry, replace the interior pane of glass and secure the locking clips.

Windows Without Breather Holes

Step 1

Prepare the area in front of each window before defogging by taping down a beach towel or small blanket on the floor to catch any excess glass from drilling.

Step 2

Mark the upper right hand corner of the window with a black marker. One small mark is sufficient.

Step 3

Use a 1/8-inch drill bit designed for drilling glass and drill a small hole on the mark in the corner of the window.

Step 4

Roll up the blanket or towel and remove carefully. Sweep away or vacuum any remaining small pieces of glass that may have dropped out of the towel.

Step 5

Wait for the window to completely defog. When the window is clear, place a piece of tape over the hole and poke tiny holes in it with a needle to allow the moisture inside the window to continue to escape. You can also leave the hole open if it's in an unnoticeable location.


Prevent thermal pane windows from fogging by running a dehumidifier in the house at all times, especially in the winter. Keep ceiling fans running at all times to help move moisture away from windows.

Keep your thermal pane window breather holes clear by performing regular maintenance on the windows a few times each year.

Make sure your windows are properly sealed and locked to prevent unwanted moisture build-up. Check to see if the seals are both clean and dry before locking.


Check your window manufacturer’s warranty before drilling any holes in your windows. This method is primarily for windows no longer covered under warranty. If your windows are still fairly new and under warranty, call your manufacturer for the best way to defog your windows. A technician will come out and examine your product for defects.