What causes condensation on windows?

Written By: Stephanie Vanderbilt, Owner

Reviewed By: Coastal Windows & Exteriors

Last updated: September 14, 2026

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Condensation on windows forms when warm, moist air touches a surface cooler than the dew point. An InstallationMasters-certified installer with 7,000+ installations completed since 2011, Coastal Windows & Exteriors is a woman-owned exterior remodeling company serving 730+ towns across Massachusetts, New Hampshire and Maine, specializing in energy-efficient replacement windows that help homeowners tell harmless surface fog from the between-the-pane fogging that signals a failed seal. Where the moisture appears on the glass tells you most of what you need to know.

What Homeowners Need to Know:

Warm meets cold: condensation on windows forms when humid air touches cooler glass. Book a free in-home estimate if it persists.
Three spots: it appears inside the glass, outside the glass, or between the panes.
Indoor humidity: cooking, showering, and humidifiers add moisture that lands on cold glass.
Exterior normal: outside condensation on efficient windows is normal and clears after sunrise.
Between panes: fog sealed between panes signals a failed seal, detailed in this broken window seal guide, not surface humidity.

Which Approach Fits Your Situation:

Top Recommendation: A free in-home estimate if condensation appears between the panes and won’t clear. Schedule your free estimate today.

Best for indoor humidity: Reduce moisture sources like cooking steam, showers, and houseplants before assuming a window problem.

Smart for exterior fog: No action needed, since it clears naturally and signals efficient glass.

Ready to figure out what your window condensation means? Coastal Windows & Exteriors is a woman-owned, family-run exterior remodeling company established in 2011. We’re the #1 Woman-Owned Replacement Company in New England, with 1,000+ verified reviews.

Request a free window estimate from Coastal Windows & Exteriors.

Browse our complete windows FAQ guide from Coastal Windows & Exteriors.

Explore the Coastal Windows & Exteriors Windows Exterior Remodeling Home Improvement Help Center.

Still have questions about what causes condensation on windows? See the areas we serve and talk to your local window contractor.

Last Updated: September 2026

Sources:

Water condenses on a window surface when its temperature falls below the dew point of the surrounding air, and condensation on the outside of a window is generally less of a concern than condensation on the inside surface. NFRC Consumer Guide to Windows, NFRC’s consumer guidance on window condensation and dew point physics. (Accessed July 2026)
Seal failure leads to the loss of insulating gas and can result in condensation from moisture penetrating between the panes. NFRC Consumer Guide to Windows, Guidance on Window Durability, NFRC’s technical guidance on insulating glass unit seal failure. (Accessed July 2026)

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