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    What You Need to Know: Condensation on Windows


    (Photo: EPA)

    (Photo: EPA)

    What is Condensation?

    Condensation, which can appear as a light coating of water, water droplets, frost, ice, or some combination of the four, forms on any surface when the temperature (°F) of that surface is less than its dew point temperature. For example, if the temperature of the glass in a window is 50°F and the dew point temperature for the glass is 55°F, condensation will form on the surface of the glass. The dew point temperature of any surface is directly related to the amount of moisture that is in the air, which is called the relative humidity. It is also related to the temperature of the air in the room, which is known as ambient air temperature. As the relative humidity in a room increases, the dew point temperature also increases, which means that a surface is more likely to show moisture even at warmer temperatures.

    As the relative humidity starts reaching levels near 100%, moisture will form on almost any surface, no matter what the temperature of that surface. For example, bathroom and kitchen areas typically have higher humidity conditions at certain times of the day. On the other hand, surfaces in living or working areas where the relative humidity is low have lower chances for the formation of condensation

    The amount of humidity in the air can rise and fall depending upon the temperature of the air. Warm or hot air has the ability to hold much more water vapor than cool or cold air. So the humidity in air is relative. Relative humidity is defined as the percentage of water vapor in a given amount of air at a given temperature. When this percentage gets to 100 percent, the water vapor, a gas, changes from a gas to a liquid. Meteorologists refer to this complete saturation as the dew point.

    What does it mean when I have moisture on the inside of the storm window (or outside pane)?

    This indicates that the prime window is allowing air and moisture to leak out to the storm window where it condenses. Stopping these air leaks with caulk and weather stripping will stop the condensation and ultimately save your window. It is also important to understand that too little humidity is bad for your house. Manufacturers claiming that low humidity (15 percent) is best for windows may be covering for a poor quality product. Good windows should not have excessive condensation at normal humidity levels (30 percent to 40 percent).

    Moisture on the inside of a window pane is a sign that airborne water is trapped in the house due to poor air circulation and exchange.

    During the heating season, the indoor humidity level should hover around 30 percent to 40 percent. When indoor humidity exceeds 40 percent during cold weather, moisture problems begin to appear. One symptom of a high humidity level is condensation forming on cold surfaces.
    High levels of humidity are often the result of too much moisture vapor generated indoors.
    HEATING AND VENTILATION magazine provides builders with reference data on sources of water vapor. For instance, cooking for a family of four adds 4.5 pounds of moisture a day to a house. Each shower contributes half a pound; a weekly laundry, 30 pounds; human occupancy contributes 6 to 3 pounds per day; dish washing 1.2 pounds, etc.

    So you see that the modern living of a family of four can easily release 150 pounds, or more than 18 gallons of water per week into the air in your home!

    All of this moisture MUST eventually escape from your home. Storm window frames are made with a breathing hole that permits condensation to escape. These breathing holes often become plugged or puttied shut over time. When this happens, moist air becomes trapped and condensation appears. To fix the problem, unplug the holes.

    Where Does Humidity Come From?

    • Normal breathing and perspiration by a family of four adds a half pint of water to the air each hour.
    • Cooking can add up to four or five pints of water per day.
    • A shower can add another half pint.
    • Dishwashers, washing machines, and dryers can add several pints of water to the air.
    • Humidifiers which are adding too much humidity.
    • Poorly insulated crawl spaces which allow humidity to invade the home.
    • New homes will often emit excess humidity for the normal drying out of the building products. This is normal and will usually adjust itself within a year or less.

    In other words, if condensation is to be reduced, the source and amount of humidity in the air needs to be determined

    Steps to Reduce Excessive Humidity
    Recognize that the best way to stop condensation is to reduce the moisture in the inside air. Here are a few tips:

    • Vent gas burners and clothes dryers to the outside.
    • Dryer and kitchen range exhaust fans should never be vented to the attic.
      Install exhaust fans in the kitchen, bathrooms, and laundry rooms.
    • Controlling or covering other sources of humidity (radiator water pans, fish tanks, large numbers of plants, etc.).
    • Installing a dehumidifier.
    • Opening fireplace damper.
    • Ventilating the crawl space or basement: Install foundation vents or leave a basement window cracked in the fall or early winter to ventilate your basement or crawlspace.
    • Another positive measure is to connect a small duct from the outdoors to the return side of a forced-air heating system, so that fresh air is drawn into the house whenever the system is operating.
    • A damper placed in this duct will allow the home owner to control incoming air. A simpler method is to simply crack a window somewhere in the home.
    • Make sure your humidifier is working correctly. Turn it down as the weather becomes colder.
    • Vent all appliances and vents to the outside.
    • Vent attic and crawl spaces.
    • Cover the earth in your crawl space with a vapor barrier.
    • Run exhaust fans while cooking or bathing.
    • If you have a forced air furnace, make sure your home is properly ventilated by installing a fresh intake.
    • Don’t store firewood inside.
    • As a temporary solution, you may want to try opening your windows a little each day to allow the exchange of colder’ drier air with warmer more humid air. This should not effect your energy bill in any substantial manner.
    • Install energy efficient windows.

    Source: McCool’s Property Inspection

    Current Conditions in Addison, TX
    Water Restrictions: Stage 1 Restrictions

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