Window Condensation: Causes, Types, and Solutions

Interior condensation forms on the inside surface of windows when warm, humid indoor air contacts the cold glass. It is most common in winter when indoor heating raises moisture levels.

Common sources of indoor humidity include cooking, showering, laundry, breathing, and houseplants. New construction materials also release moisture as they cure.

Solutions for interior condensation: reduce humidity with exhaust fans and dehumidifiers, improve air circulation near windows, and upgrade to insulated glass with warmer interior surfaces.

Exterior condensation forms on the outside of windows on cool, clear mornings. It occurs when the outside glass surface is colder than the dew point of the outdoor air.

Exterior condensation is actually a sign that your windows are working well. Highly insulated windows keep the outer pane cooler, which is why newer, better-insulated windows may show exterior condensation that older windows did not.

Exterior condensation evaporates naturally as the air temperature rises during the day. No action is needed.

Condensation between the panes of double or triple-pane glass indicates a failed seal. When the seal breaks, the insulating gas escapes and moist air enters the gap.

Between-pane condensation cannot be cleaned because the moisture is trapped inside the sealed unit. The insulated glass unit (IGU) must be replaced.

IGU replacement is straightforward and does not require replacing the entire window frame. A new sealed unit is measured, ordered, and installed in the existing frame.