Every year we get more calls on window condensation. Let me be clear, I am not talking about condensation between the two sheets of glass that make up the IG (insulated glass) unit. This is referred to as a “seal failure” and is addressed in the window warranty. This article is about condensation that can be wiped off of the window. Though condensation can occur on both the inside and outside face of the window, most complaints come from condensation on the inside pane of glass and that is what we will address in this article.

Most homeowners that call with this issue are sure the condensation is caused by a failure or problem with the window. They could not be further from the truth. The reason one can experience more condensation on their new windows then was experienced with the old drafty ones is the old drafty windows allowed humidity to escape. New windows have a much tighter seal so the water vapor can no longer escape through the window. Condensation is an indicator the window is working properly not failing.

First, to understand the issue one must first understand condensation. Condensation is the change of the physical state of matter from gaseous phase into a liquid phase. In this case water.
The amount of condensation one might experience on the inside pane of glass of a window is a direct result of the humidity level in the building (home). All air contains some level of moisture. All homes have occasional condensation such as a little fogging on the window and is no cause for concern. On the other hand, excessive window condensation, frost, peeling paint, even moisture spots on the ceiling and walls can be signs of excessive condensation which can potentially cause extensive damage to a home.

With modern building techniques we are constantly striving to make homes more energy efficient and air tight. In older homes with old inefficient windows, old poorly insulated walls and ceilings and old siding, air leaking and infiltration is a common trait. These traits are terrible for energy efficiency but helped keep the humidity levels down. When homeowners changed out the windows, insulated the walls and ceiling, caulk and seal joints and added better siding, the air leaks are dramatically reduced, energy efficiency is greatly increased but unfortunately interior humidity levels can also be increased. The first place a homeowner will usually see the effects of this increased humidity level is on the glass of the windows and mirrors because moisture doesn’t penetrate these surfaces. So naturally homeowners blame the new windows.

The water vapor (humidity) will condensate when the temperature surrounding the water molecule reaches the dew point (saturation level). The higher the humidity levels the higher the dew point temperature where condensation will occur. The modern family of 4 can easily release 150lb or 18 gallons of water per week into the air of the home through cooking, showers, laundry, dish washing, cleaning and human occupancy. Indoor plants, laundry that is drying indoors, interior painting, and crawl spaces with no vapor barriers, all contribute to high vapor levels. You can stop or at least minimize condensation by monitoring the amount of water vapor in the home by applying the following steps. Air out your home periodically, and opening windows for just a few minutes a day. You make sure that there is nothing blocking the foundation or attic ventilation of the home. You should insure you have exhaust fans in the kitchen and bathrooms and use them after humidity-producing activities to vent the moisture. You should check to see that they exhaust outside and not into the attic. If these normal ventilation methods are not sufficient, you may have to contact a heating and air specialist for additional forced venting or dehumidifying systems.