One of the questions we are often asked at Hometown is about condensation — moisture that appears on the inside or outside of the glass surfaces of windows and doors. Moisture on the surface of the glass can be annoying — blocking your view, dripping, or pooling. And condensation isn’t strictly a problem associated with old, drafty windows and doors, but can even affect brand new, energy-efficient products under the right conditions. Understanding what causes condensation to form can help homeowners prevent it.

Exterior Condensation on Windows and Doors

Condensation on the exterior of windows or doors, or dew, is a natural atmospheric phenomenon. When air humidity levels are high, moisture will condense on any surface of a temperature lower than the dew point of the air. You may see this form of condensation on your automobile, lawn furniture, or on streets and lawns, especially on spring and fall mornings, when cool nights follow warm days.

Just like the moisture that forms on a glass of ice water on a hot day, this type of condensation results from warm air, saturated with moisture, coming into contact with cooler surfaces. The cooler the air, the less moisture it can hold, so the cooled air next the surface of the glass causes the moisture to come out of the air and condense. In Indiana and the surrounding region, this type of condensation is more common in the spring and fall because nights are cooler, causing the surfaces to cool down. As the sun comes up and the air temperature rises, those cooler surfaces become a perfect place for condensation to form.

While this type of condensation might be annoying or inconvenient, it really isn’t anything to worry about. Typically, it will burn up as the surfaces heat up.

Interior Condensation on Windows and Doors

Condensation on the inside surfaces of your windows or doors, however, can be not only bothersome but possibly an indicator of other problems. Interior condensation technically happens by the same process and under the same conditions as the exterior — humid air condenses on surfaces that are cooler than the air temperature. But inside the home, overly humid air can cause more problems than just moisture on windows and doors.

Excessive humidity will produce a “damp” feeling in the home. You may notice papers wrinkling, discoloration of fabric surfaces, warping of wood floors or moldings, peeling or blistering paint, sweating pipes, mold, mildew, or a “musty” smell in the air. If you notice condensation on the inside surfaces of your windows and doors or pooling in the corners of the frames, it may be because the relative humidity of your home is too high. Humidity higher than 65% can even cause difficulty breathing for people who suffer from allergies or asthma.

Moisture is introduced to your home’s air in a variety of ways:

  • In new construction, building materials put off a great deal of moisture. This gradually diminishes as the home ages.
  • Baths and showers — an average shower adds a half-pint of moisture into the air.
  • Cooking — the preparation of 3 meals per day adds as much as 4 or 5 pints of water vapor to the air.
  • People — normal respiration and perspiration of a family of four adds about a half-pint of moisture into the air.
  • Daily Activities — anything that uses water, such as dishwashing, laundry, mopping, etc. produces water vapor.
  • Other factors — houseplants, gas appliances, kerosene heaters, or the burning of any fossil fuels all produce water vapor.
  • A family of four may introduce as much as 18 gallons of water per week to the hair in their home!

All this water increases the relative humidity of the air in the home. For the comfort of those who live there and to minimize potential damage to the structure itself, humidity in the home should be regulated to a desirable range. Just as too much humidity can be bad, so can air that is too dry. We’ve all experienced a ZAP! when we grab a doorknob after walking across a carpet. Static electricity, and dry or itchy skin can result from relative humidity that is too low. Experts generally agree that an indoor humidity level in the range of 30% – 50% is both comfortable and healthy.

Measuring and Controlling Humidity

Besides just paying attention to the signs of humidity that is higher or lower than the ideal range, you can measure more precisely with an inexpensive device called a hygrometer. A hygrometer can be purchased at a hardware store for as little as $5 – $15. Relative humidity fluctuates with the seasons, the temperature, and activities of daily living. If you have a newer, programmable thermostat, it may include a hygrometer. Some HVAC systems also include humidifier/dehumidifier features to maintain the relative humidity in your home in a desirable range.

If the relative humidity in your home is too high, here are some things you can do about it:

  • Consider the use of a dehumidifier.
  • Make sure the attic and crawl spaces are adequately vented. A house that is too weather-tight traps humidity inside instead of allowing it to escape. The home needs to breathe a little! Ironically, as building products (including windows and doors) have improved in energy efficiency, houses not only keep outdoor air out, but also trap warm moist air in.
  • Run an exhaust fan (properly vented to the outdoors) in the bathroom whenever showering.
  • Make sure all gas appliances such as the clothes dryer and furnace are properly vented to the outside.
  • Install a vapor barrier over the earth in the crawl space.
  • Do not store firewood indoors.
  • Use an exhaust fan (properly vented to the outdoors) in the kitchen whenever cooking or running the dishwasher.
  • Drawn drapes and closed blinds trap cold air against a window or door, possibly causing condensation. If you have noticed condensation on your windows or doors, leave the curtains and blinds open when possible. Consider using a fan to circulate air near windows or doors where condensation has been an issue. Bay or bow windows are more susceptible to condensation as airflow near them may be somewhat restricted.

If your relative humidity is too low (more likely in the winter months in central Indiana), you can easily introduce more moisture into your home:

  • Use a humidifier.
  • Place open containers of water on registers, window sills, or even on candle warmers.
  • Get some houseplants.
  • Hang your clothes to air dry.
  • Open your dishwasher when the clean cycle is over and allow dishes to air dry.

If there is Condensation on Your Windows and Doors

  • If the condensation is outside — don’t worry about it.
  • If the condensation is inside, and only occurs occasionally, when conditions are just right, go ahead and towel it off because prolonged exposure to moisture may damage wood frames, but it probably isn’t really anything to worry about too much.
  • If the condensation is inside and occurs regularly, then perhaps it is time to consider some of the humidity control measures discussed. If you think the issue has more to do with too much cold air getting through your aged windows and doors than it does with excess humidity, then give us a call for a free, no-obligation quote on replacement.

Because condensation is such a common concern among homeowners, Andersen Corporation has created this informative brochure, Guide to Understanding Condensation.