The Stack Effect

As warm air rises in a home, it leaks out of the upper levels. New air must enter your home to replace the air that has escaped. In fact, in a tight home, about half of the air escapes each hour out of the upper levels. This creates suction at the lower levels to draw in replacement air. In older homes, the air exchange rate can be as high as two exchanges per hour.

What this stack effect does is create airflow in your home from bottom to top. So air from the crawl space is drawn upwards into the first floor living area and then into the second floor. Of course, it dilutes with other air in your home, but building scientists say that up to 50% of the air you breathe on the first floor is air that came from your crawl space.

Therefore, whatever is in your nasty crawl space air (mold spores and humidity) is in the living area of your home and can negatively affect your family. If there is mold or mildew in the crawl space, mold spores are floating around upstairs that your family is breathing in.

So this idea that we put in crawl space vents and expect that air will flow in through vents on one side of the house and out through the vents on the other side, does not happen. What actually happens is air enters the vents in the front, enters the vents in the back, and enters the vents on the sides of the home and then it goes UP!

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