Is it really possible to defog an insulated glass window?

Disclaimer: The views and opinions expressed in this article are those of the author. Examples of analysis performed within this article are only examples. They should not be utilized in real-world analytic products as they are based only on very limited and dated open source information. Assumptions made within the analysis are not reflective of the position of any one but the author.
Window with clouded insulated units
Window with clouded insulated units

I regularly get calls from customers that have cloudy insulated units. Most of them ask one of the following questions:

  1. Does the whole window need to be replaced?
  2. Can you replace the glass only?
  3. Can you remove the “fog”, “dirt”, “moisture” from the inside of the existing glass?

Before I comment on the above questions, I will define a typical insulated unit.

The majority of insulating glass units consist of two lites of glass enclosing a hermetically sealed air space.The lites are held apart by a spacer around the perimeter. The spacer contains a moisture-absorbent material called a desiccant that serves to keep the enclosed air free of visible moisture. The entire perimeter of the assembly is sealed.

Window with visble moisture
Window with visble moisture

A window is considered “foggy” or failed when there is visible moisture between the glass.

  1. Does the whole window need to be replaced?  In most cases, no.  There are some windows that have very specialized framing or glass that needs to be replaced by the original manufacturer.Can you replace the glass only?
  2. Can you replace the glass only?  This it what can be done in about 90 -95% of windows.  It can usually be done with only minor finish touch-up required on the frame.
  3. Can you remove the “fog”, “dirt”, “moisture” from the inside of the existing glass? Not cost effectively.   Several times a month,  a customer tells me that someone they know had someone come out and drill some holes in the glass and clean it out. I always tell them to call that person and ask them who did it.  The response is they forgot who or that they are out of business. There is no company that I am aware of in the Chicago area that does this process.

I found several patents describing the process.

System for alleviating in-vault condensation in double-glazed windows

Method of treating a glazing panel

I will now critique the process and show that even if it would work, it is not cost effective or practical.  In fact the Canadian company that owned and used the former patent is no longer in business.

  1. Both methods require drilling holes in the glass. It is a messy process and it is impossible to do in tempered glass.  All doors and many other locations require the use of safety glass.  Most safety glass is tempered. The latter patent recognizes this issue and then describes a method in which a hole is drilled through the side of the frame through spacer.  There are many problems with this solution.

 a. This could possibly damage the structural integrity of the frame.        b. You now are drilling through the metal band and desiccant.  This      will cause some to fall between the panes of glass.                                  c. Not all windows can open to get to the side.

2. After the holes are drilled, a “cleaning solution” is to be inserted in the unit.  This really confounds me as I fail to understand how this will be able to clean the entire inner surface.  It also will get the metal spacer wet and the desiccant will absorb it.  As anyone who as ever cleaned windows knows, this will most likely leave streaks.

3. If you get past the above problems, you have the issue of how to plug the holes.  Imagine how the window with numerous lites that leads this post would look with all these little holes in the glass.

There does not seem to be a company in the Chicago area that does regularly does this work.  This indicates to me that either the process does not work, or is not a feasible business!


Why do my windows have condensation?

Water or frost on windows is condensation. Condensation is formed when warm moist air comes in contact with cooler dry air. An example of this is when a bathroom mirror “steams up” after a hot shower. Just like that mirror, the inside or outside of your window can sweat or fog because of temperature differentials.
Faulty windows do not cause condensation. Glass is usually the first place you notice condensation because glass surfaces have the lowest temperature of any surface in a house.
The moisture in the air causes condensation. The reason you may observe more condensation in your home is because of modern energy-efficient homebuilding techniques and products.
The insulation and construction materials used today are designed to keep cold air outside. This is especially true of new windows. While energy-efficient designs and weather-stripping keep cold air outside, they also keep warm moist air inside. Older window designs were less efficient and consequently allowed moisture to escape.
If you didn’t have as much condensation before replacing your old windows, it’s probably because they were drafty. Good windows and insulation all create barriers to the air exchange of a home. When combined with the additional water vapor (moisture) from showers, cooking, or from clothes dryers not vented to the outside, the result is excess moisture and a high relative indoor humidity level.

The key lies in controlling the humidity inside your home. First, let’s understand where the moisture comes from. During the hot humid summer, your house absorbs moisture. The same principle applies to a newly constructed or remodeled home, due to the abundance of moisture from the building materials used in construction.
During the beginning of the winter when you start to heat your home, condensation occurs. After a few weeks, your home will begin to dry out and you’ll see less condensation. Opening a window briefly is a quick temporary solution. The drier cold air will enter the room while the moist air is allowed to escape.
Other solutions that may reduce condensation include:
• Cracking open a window or door daily to air out your house.
• Opening a window or running exhaust fans longer in the kitchen, bathroom and laundry room.
• Opening drapes and blinds, allowing air to circulate against windows.
• Turning off any humidifying devices in your home.
• Installing and using a dehumidifier.

If you live in a northern climate, the above steps, as well as the following points, may be relevant:
• Adding storm windows or replacing existing single-pane windows with insulated windows.
• Keeping plants in a sunroom or in rooms that are infrequently used during extreme cold weather.
• Adding waterproofing protection to basement floors and walls.
• Removing radiator pans until sweating has been eliminated.
• Making sure that open-faced gas heaters are connected to a chimney and using them as little as possible.

Window condensation should only occur when there are extreme temperature differences between indoor and outdoor spaces. In addition, there should only be a fairly small amount of water on the glass. Condensation will be seen on the inside of a window during winter months, and will present itself on the outside of a window during summer months.
If you find condensation between the two layers of glass in an insulated window, the airtight seal has probably been broken and the glass will need to be replaced.

Is it really possible to defog an insulated unit?