Triple pane window construction consists of three layers of glass. Between the center layer and each of the outer layers is a layer of gas, such as argon or krypton. Called fill gases, they insulate the glass, reducing the amount of energy lost through the home's windows. Triple pane windows create a barrier between the warm dry air inside your home, and cold, more moist air on the outside. Condensation, or fog, on these windows indicates that they are no longer doing their job.
Fogging of triple pane windows is the result of one side of the glass being a different temperature and moisture level than the opposite side of the same glass. The sweat that forms when this happens can be damaging to your home's exterior at worst, and at best, blocks or clouds your view through the offending window. Window glass responds to environmental factors the same way as a glass full of ice water sweats outwardly on a hot day.
The presence of fog on the outside of the window indicates that the triple pane window technology has failed. In new windows, it could be anything from a manufacturer's defect to improper installation procedures. In older windows, it is usually caused by a leaking seal. As these windows age, the seals may break down and allow air and humidity in between the panes, while at the same time releasing the insulating gas and resulting in fogging.
Sometimes the fog occurs on the inside of the triple pane window. It is almost always caused by too much moisture inside the home. With new homes this is a common problem as the new building materials are still in the process of drying out. In older homes, adjusting the humidity inside the house to reduce the relative humidity should solve the problem.
Sometimes your location can affect how much fog appears on the windows. For instance, parts of the United States where average winter temperatures are 35 degrees Fahrenheit or lower see more condensation problems due to the large discrepancy between indoor and outdoor temperatures. Areas with warmer winters do not usually have problems with fogging windows. Triple pane windows are an ideal choice for colder climates because their technology reduces the instance of outdoor fogging.