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