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  • Moisture beading up on your windows and distorting the view may be annoying. But it means you can breathe a sigh of relief, confident that your home is well weatherproofed.

    Definition

    Condensation is the conversion of vapor to liquid. It happens when a parcel of air cools to the dew-point temperature at which air can no longer hold water vapor.

    Exterior Condensation

    When moist air outdoors hits cool window glass, condensation collects on the exterior surface. A cool night after a warm, humid day in spring presents perfect conditions for this.

    What Exterior Condensation Means

    A window collecting exterior condensation is providing good insulation, keeping the heat inside instead of conducting it outdoors. Exterior condensation frequently forms on low-emissivity (Low-E) coated windows, which can reduce heat loss by up to 50 percent.

    Interior Condensation

    Excess humidity inside the house causes condensation to form on the coolest portions of the wall, typically the windows.

    What Interior Condensation Means

    The more interior condensation, the higher indoor humidity. On the plus side, this indicates a home well sealed against indoor/outdoor airflow. But excessive humidity indoors can lead to mold.

    Reducing Interior Humidity

    Ensure moist air has an escape route by opening your fireplace damper and using exhaust fans in the kitchen, laundry and bathrooms. Open windows for a few minutes each day to air out your home.

    Source:

    Arctic Climatology and Meteorology Glossary: Condensation

    Arctic Climatology and Meteorology Glossary: Dew Point

    Gorell Windows & Doors: Understanding Condensation

    More Information:

    Efficient Windows Collaborative: Window Technologies: Low-E Coatings

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