Relative Humidity

Crawl Spaces Have a High Relative Humidity

The air in a crawlspace is naturally cool, maintaining an average temperature of fifty degrees because of its tendency to draw its temperature from the earth around it. Although a crawlspace has a high relative humidity, cooler air holds less moisture than warm air. As a matter of fact, when you run a dehumidifier, it works by cooling the air on a coil so that the relative humidity rises until the moisture is forced out.

In the summer, when the crawlspace vents let warm, humid air in, the air in the crawlspace cools the outside air. As the air cools, it can hold less and less moisture, and the relative humidity raises up dramatically. If the cooling air has more moisture than it can hold, where is that moisture going to go?

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