What Exactly is Stack Effect?

Stack effect is the movement of air into and out of buildings, chimneys, or other containers, resulting from air buoyancy.  Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences.  To put it more simply, air leaks out at the top, which causes air to leak in at the bottom of anything that is contained.

This is especially true when applied to your home—as warm air rises and leaks out of the upper levels, new air enters in through your basement to replace what was lost.  With low air pressure on the lower levels, the home sucks on the ground, then blows air out of the upper levels due to a higher air pressure.

In the average home, about half of the air in the escapes each hour out of the upper levels.  In older homes, the air exchange rate can be as high as full air exchange per hour.  So why is this necessarily a bad thing?  Well, studies have shown that 50% of the air you breathe on the first floor in your home is air that came from the basement.  Therefore, whatever is in the air in your basement may be affecting you more than you think.

Many people think that if their basement is leaky or moldy it doesn’t matter because they never use it anyway.  However, if there is high humidity downstairs, then there is even higher humidity upstairs than there would be otherwise.  If there are mold spores or damp odors in the basement, then there are mold spores or damp odors upstairs.  Studies have shown that prolonged exposure to mold can actually cause asthma, as well as irritate people with existing asthma and mold allergies.

Since stack effect is a phenomena that will always occur, sealing off your basement as well as getting rid of any mold or odors is the best way to ensure that your family will be breathing healthy air in your home.