By Phillip Schmidt, Networx
Most experts agree that condensation or fogging inside of a double-pane window technically is not a fixable problem -- at least not in the sense that your window can be restored to its original level of performance. Presently, there are two different ways to deal with condensation: either replace the window (you can usually replace only the glass unit and not the whole window) or hire a local company to drill holes in the outer pane, clean the windows from the inside and install one-way air vents to help prevent future condensation.
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If your condensation problems are in a sliding glass door or a window that is likely to have tempered glass (for example, if the window has more than 9 sq. ft. of glass area and is less than 18 inches above the floor), your only option is replacement. This is because it's essentially impossible to drill tempered glass without breaking it. You should assume that all doors with double-pane glass areas large enough to fit a 3-inch sphere through them are made with tempered glass (or in some cases, laminated safety glass).
Replacing Double-pane Windows
Double-pane windows, also called "insulated" or "thermal" windows, are made with two panels of glass sandwiched over a spacer and sealant, creating a space between the panes that is filled with air or with a gas, usually argon or krypton. It is this sealed space that gives the window most of it's thermal performance. The spacer may also contain a desiccant material to help absorb and moisture in the air within the sealed space. Condensation in a thermal window typically indicates a failure of the seal between the glass panels and/or saturation of the desiccant.
Because a breached seal allows fresh air and water vapor to enter the window space, a condensation problem simply becomes a function of nature. Condensation is also a sure sign that gas-filled windows are no longer so. And since there's no way to re-seal an insulated window, replacement of the glass is the only option for restoring maximum thermal performance, in addition to solving the condensation problem. As mentioned, most glazing on insulated windows can be replaced as a unit, which saves you the expense and remodeling work of replacing the entire window, frame and all.
If your windows are still under warrantee, the first step is to contact the supplier or manufacturer, since replacement may be free. If the warrantee has expired, it's still a good idea to consult with the manufacturer to discuss the recommended replacement options. Many local glass companies can also fabricate new window units in any size.
While insulated window restoration companies may claim that their processes can restore most of your window's thermal performance (in addition to eliminating condensation), these claims remain hotly disputed.
Restoring Insulated Windows
The only way to rid a thermal window of condensation is by removing the moist air in between the panes and replacing it with dry air. And there's a professional service based on this very technique. Thermal window restoration or repair companies come to your house and drill a small hole (3/8-inch or so) at one top and bottom corner of the affected window. They spray various liquid solutions onto the inside faces of the panes through the top hole and suck them out through the bottom hole. Once the window is clean and dry, the holes are sealed with little vent plugs that allow air and water vapor to escape the window cavity but don't let them back in.
Will this process work for your windows? It might. Or it might not. There are numerous consumer accounts in both directions. In any case, restoration companies commonly claim that their process costs 1/3 to 1/2 as much as glass replacement. And don't even consider a service that doesn't offer a money-back guarantee.
Deciding Which Way to Go
This can be a tough call, and you should examine your options carefully. If you decide to try restoration and it doesn't work, you won't really devalue the window further, since it has already failed. On the other hand, if the restoration isn't satisfactory and the company doesn't make good, you'll be out the cost of restoration and will still be faced with paying for new glass. Of course, if thermal performance is a high priority, replacement is clearly the best option.
Source: http://www.networx.com/article/how-to-fix-condensation-in-double-pane-w
