for Cold Climate Housing and much more

Last Updated: , Created: Saturday, October 31st, 2009

PROFESSIONAL SERVICES -- removing the fog from thermal pane windows.


When condensation shows up inside a thermal pane double window (between the two pieces of glass), you know that the seals around the edge have been compromised, allowing moisture to get inside. These cannot really be re-sealed so the standard response to this problem is to replace the glass unit. That is expensive.




If the window frame and the mechanisms are in good shape you may want to consider changing just the thermal glass unit rather than the entire window. There are glass repair shops that can help you to decide if this is your best option. 

See the comments section at the bottom of this article to write and read about these professional services.



Alternatively you might want to consider a new and growing service that takes something that we used to do with great fear of breaking glass (see my web entry on moisture in windows), drill some holes to let the sun dry out the window.

In fact the professional services process does much more than just drilling holes in the windows. They wash out the space inside the thermal pane window and put in a permanent valve that keeps the window clear even though the seals are broken. They can even fix scratches on the glass just like you have done to the windshield of your car. The process won't bring every old foggy window back to life, for instance when the moisture has etched into a Low-E coating on the inside, that cannot be repaired. That is one reason to have windows repaired as soon as you see the first signs of moisture inside between the two pieces of glass.

You will probably find this service more expensive than you expected so before you ask for an estimate for this clearing and venting process, get an estimate for the cost of replacing the glass unit or replacing the whole window so you will know which choice of the three is most economical in your case. Although it is generally less expensive than replacing the entire window, it is not worthwhile doing if the rest of the window is reaching retirement.

Yes windows will be slightly less efficient with a vent valve installed than if that space were effectively filled with special insulating gasses -- but it will be more efficient than a window filled with humidity as moisture inside the window actually conducts heat towards the outdoors.

One of the great aspects of this process is that it works continually, so if more moisture wants to sneak into the window, it is kept clear, and it keeps an even efficiency over time equal to a newly installed window that did not have insulating gas.



Remember to do your financial math. If the window or door frame is really shot, don't bother to spend the money on getting the glass clear. If you have several years service left in the frame and hardware, then an investment in clearing the window should be worth it. In one place at one time (prices change all the time) having a new thermal pane installed in a patio door cost about $350, while having the old one professionally cleared with a 10 year guarantee was about $200. A whole new patio door installed was close to $1,000.



The whole process was started by Crystal Clear Window Works out of Ottawa here in Canada.  They have since gone out of business and left a lot of noise behind about a lot of lower cost poor workmanship in the field that drove them out of business.   I have not yet found a company that I have confidence to recommend and although the process is great, one must demand several references of any proposed services.  By the way, if they suggest drilling holes on the inside house side of a thermal pane window, they just don't know what they are talking about in a cold climate. The holes must be on the dominantly cold side -- which means the snow side in Canada -- the house air conditioned side in Florida. 

If you have had a good experience with a thermal pane cleaning company, please share that with us in the comments below.


Keywords: Condensation, Humidity, Moisture, Glass, Fog, Frame, Patio Doors, Windows, Products, Cleaning, Seals, Financial, Scratches, Investment, Valves, Problems

Article 2069

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Gretchen on September 05, 2023 15:42

which side of the window are you drilling in your article? my window is a triple glaze and I drill the hole on the outside?

Hello Gretchen,

When clearing water from a double pane window by vent holes, in a cold climate you always drill through the outside pane of glass (the opposite in Florida). If you put the hole on the inside, it will actually draw more household moisture into the air space, rather than expel the moisture out.

But a triple pane window is a more complex situation. You have two air spaces, one we can call the inner air space, the other you can call the outer air space. If you have moisture in the inner air space, the vent system will not work for you at all because you cannot vent the inner space to the outdoors.

Technically, if your have moisture in the outer air space, you could introduce vent holes on the outside as with a double pane window and clear that space. But it is probably not worth the cost because moisture in any air space is an indication that the spacer seals between the pieces of glass are failing for one reason or another and it will probably not be long before the second air space will fill with moisture as well.

I doubt that venting thermal air spaces to prolong the life of a triple pane window is a viable option.

Sorry about that


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