Causes of Condensation on the Exterior of Windows

By Eric Benac

Condensation is a light buildup of water on a surface, which occurs often on windows on the inside and the outside. Many different causes are attributed to condensation on the outside of the window. Understanding why condensation accumulates on the outside of your window can help you treat this minor problem. Though it won't damage your windows, it is very unsightly.

Weather Changes

If you experienced a cool night followed by a warm morning and day, the outside of your windows may have excessive condensation, which happens most often during the spring and fall seasons when the weather fluctuates more often. Summer and winter are generally pretty steady with their temperatures, but spring and fall have shifting and unpredictable weather patterns. The rising temperatures raise the dew point outside the glass. The glass of your window may still retain some of the cold from the previous night. As a result, there is an imbalance between the dew point on the glass and the dew point outside the glass, which is corrected when condensation forms on the window.

Excessive Humidity

If the air outside of your window is excessively humid, it can create condensation on the outside of the window, which is true only if the humidity on the outside of the house is higher than humidity inside the house. Several reasons exist as to why the humidity might be higher outside than it is inside. The first reason is that it is simply a very still day outside. The reason this can cause excessive humidity is because wind helps the water in the air evaporate. Almost all of the water in the air is caused by evaporation. Blowing wind moves the water vapor in the air to a new position, which makes the area that originally contained that air more dry, which causes the moisture below this area to evaporate quicker as it rushes to fill in the area left by the newly dry air. The water vapor stays stagnant on still days, making it evaporate much more slowly. Excessively hot days can also cause more water to evaporate, creating more humidity. If you live near a body of water, you are likely to experience outside condensation on hot days.

Air Conditioning

Driving during the summer is sometimes difficult to endure without air conditioning; however, using excessive amounts of air conditioning can lead to condensation on the outside of your windows, which is also true if you use excessive air conditioning in your home. However, this is more likely to occur in your car, where the area to cool is much smaller. The essential reason for this is the excessive heat on the outside of the window. The temperature difference between the cooler window and the hotter air outside creates the same dew point imbalance as when the weather changes; however, this is caused by artificially lowering the temperature inside. Running your air conditioner at a lower speed and a slightly warmer temperature helps to avoid this problem.