Understanding and Preventing Window Condensation

Preventing window condensation problems is one of the keys to insuring the long life of your windows. Condensation is caused when the surface of the window is cooler than the dew point of air that comes in contact with the window, and this can occur either on the window’s surface or between panes. Surface condensation is typically not as serious, but can cause damage to the glass or frame as well as the interior of the house. Condensation between the panes can be harder to prevent in certain climates and generally requires complete window replacement.

Here are some tips and info from American Exteriors to help you address window condensation and prevent it when possible.

Surface Condensation

It’s counterintuitive, but condensation you can touch on the surface of the window (the season determines which side) is usually a sign of energy efficiency in the home. “Tight” homes have fewer drafts, and moisture and heat are better contained, causing the temperature of the glass to be at or below room temperature during the winter and above room temperature in the summer.

Condensation during the winter, which occurs on the interior of the home, can be destructive and lead to mold, decay, and paint problems due to excess moisture in the home.

If the condensation is minor, warming the window surface by opening drapes or raising the indoor temperature slightly can solve the problem.You can also help prevent condensation by reducing the relative humidity inside your home. This can be done by keeping your house well ventilated. Make sure the exhaust fans in your kitchen and bathrooms are up to date and run them when necessary. A dehumidifier also helps to reduce moisture in the air.

Condensation Between Window Panes

One especially damaging form of window condensation occurs between the panes of double and triple hung windows. These types of windows consist of two or three panes of glass with a spacer between them. The space between the panes is filled with insulating air or gas.When the seal on a thermal window pane fails, the air between the panes is pumped out and heat is allowed to get between the glass.Often this happens when humid air is drawn in as the window cools.

During the day, sunlight heats the window causing the air inside to expand.At night, when the temperature cools down and the sun is not shining on the window, the air cools, causing contraction.This process, known as solar pumping, is a normal occurrence in windows, but it puts pressure on the seal, which causes it to eventually fail.The seal failure is what causes condensation. Left uncorrected, this type of condensation can cause “river bedding,” where vapors form droplets that run down the window, ultimately etching grooves in the glass. It can also cause silica haze, in which saturated silica appears as white snowflake-like deposits on the glass. This type of damage requires window replacement.

The best method for preventing condensation between panes is to install quality replacement windows.

Have questions about window condensation or replacing your windows? Join the conversation with American Exteriors on Facebook.

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