Fogged Glass / Condensation / Seal Failure
Moisture or fog on a window does not automatically mean the window has failed. The first question is where the moisture is located: on the interior surface, exterior surface, or between the panes.
A Simple Test
If the moisture can be wiped off the glass, it is surface condensation rather than moisture trapped between the panes. It may be an interior or exterior condition.
Interior Condensation
Interior condensation occurs when warm, humid indoor air contacts glass that is cold enough to reach the dew point. Indoor humidity, outdoor temperature, glass temperature, window coverings and airflow all affect condensation. Even a high-performing window can develop interior condensation during very cold West Michigan weather if indoor humidity is high.
Exterior Condensation
Exterior condensation can occur on cool, humid mornings when the outside surface of the glass falls below the outdoor dew point. Efficient windows can experience this because less indoor heat reaches the exterior pane. It often disappears as temperatures or sunlight change.
True Insulated Glass Seal Failure
When the seal around an insulated glass unit fails, moisture can enter the sealed space. Fogging, haze, water droplets or mineral deposits between the panes cannot be wiped from either surface.
Does a Failed Seal Mean the Whole Window Must Be Replaced?
Not always. Depending on the manufacturer, age, warranty and window construction, the insulated glass unit or sash may be replaceable without replacing the entire window.
Related Window Terms
Insulated Glass Unit • Low-E Glass • Argon • Glass Spacer • U-Factor • Indoor Humidity • Dew Point