Window Condensation

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For homeowners, condensation on the inside or outside of their windows can be a troubling sight, but they may not fully understand the cause or implications of it. Not only is this phenomenon unattractive, it also poses serious health risks and can damage the window over time.

If you’ve ever wondered why condensation forms on your windows or how to stop it, take a look at our answers to some of the most common questions below.

What causes condensation on the outside of windows?

This is a common sight during spring and fall, when a warm day transitions to a cooler night.

How does Low-E glass impact condensation on the outside of a window?

Low-E glass is designed to maintain comfortable conditions inside by reducing heat loss through the window, in some cases cutting heat transfer by 50 percent. As the glass reflects the heat energy back into the room, the temperature of the glass exterior falls, which can lead to condensation. But in this case, the presence of moisture outside actually signals that the glass is performing properly.

How does condensation form on the inside of a window?

Condensation on the inside of a window is usually a sign of excessive humidity in the home. Due to high levels of moisture in warm air, it can often result in condensation when coming into contact with a cooler surface, such as a window pane during winter.

Are windows responsible for condensation?

No. Properly sealed and installed windows minimize heating and cooling loss, which is a leading cause of condensation. This reduced air leakage ensures that humid air remains inside. When condensation appears on well-insulated windows, it could mean that moist interior air has not been allowed to escape, but homeowners can take a number of steps to control this process.

How do I stop condensation from forming on my windows?

You can reduce condensation on your windows by promoting air flow and reducing humidity inside your home. When the temperature outside begins to fall, you may need to take certain measures to control humidity levels inside. Some of these measures include:

  • Using an exhaust fan in the kitchen, bathroom and other rooms where high levels of moisture are often present.
  • Turning off or turning down humidifiers when they aren’t needed.
  • Ensuring that all ventilation channels leading outside are unobstructed.
  • Allowing air to circulate freely through your home for short periods every day.
  • Venting clothes dryers and gas appliances to direct moisture outside.
  • Opening the fireplace damper occasionally to allow moist air to escape

If your home’s windows are not well-insulated or haven’t been properly installed, your ability to control condensation will be limited. Over time condensation on windows can contribute to mold growth—a destructive presence hidden inside window and wall openings.

Mold is increasingly being linked to child asthma, as well as increases in general respiratory illness, allergies and outbreaks of fungal disease.