Learn what causes window condensation, when it's a problem, and how to prevent it. Expert tips for maintaining clear, efficient windows.
Window condensation occurs when warm, moist air contacts a surface that is below its dew point. There are three types of window condensation, and each has different causes and implications. Interior condensation forms on the inside surface of the glass and is the most common type, especially during cold weather. It is caused by excess humidity inside the home from cooking, showering, humidifiers, and even breathing. Exterior condensation forms on the outside surface and actually indicates that your windows are performing well — the glass is insulating so effectively that the outer pane stays cool enough for morning dew to form.
Condensation between the panes of a double- or triple-pane window is the most serious type, as it indicates a failed seal that has allowed the insulating gas to escape and moisture to enter. This type of condensation cannot be wiped away and typically requires replacing the insulated glass unit or the entire window. If you notice persistent fog or moisture trapped between your glass panes, it is a sign that the window seal has failed and the window's energy performance has been significantly reduced.
Preventing interior condensation involves controlling indoor humidity levels and improving air circulation. Use exhaust fans in kitchens and bathrooms, run a dehumidifier during humid months, and keep air circulating near windows with ceiling fans or open blinds. Upgrading to high-performance windows with lower U-factors and warm-edge spacers also helps, as the interior glass surface stays warmer and is less likely to reach the dew point. Our Condensation Guide helps you diagnose the type of condensation you are experiencing and provides practical solutions for every scenario.