News and Events: Our Blog

The Stack Effect and Your Home

Thursday, March 12th, 2015 by Stacie Ellis

When you heat outside air that comes into your home, it becomes lighter than colder air.  This is why hot air rises to the top of your house and leaks out of many dozens of places—both small and large.  Since your attic is vented, think of the attic as being outside.  For all of the air that leaks out the top of your attic, that same amount of air must be replaced by being sucked in at the bottom of your home.  This is what’s known as “The Stack Effect.”

The air that leaks out of your home is a waste of heat, comfort, and money.  The air that leaks in is cold in the winter, hot and humid in the summer, and brings along dust and other allergens.  In order for you to be comfortable in your home, you have to either heat or cool this air, both of which cost money.  But once the money and energy is spent to make the air comfortable, it leaks out the top of your home, and the cycle starts all over again.  So what can be done about this problem?

The Stack Effect is unavoidable.  It’s a law of nature that’s bound to happen.  But there are steps you can take to limit the amount of air that is leaking out of your home, therefore saving you money in the long run.  By sealing air leaks in the top of the house, you can make rooms in the lower levels less drafty without actually doing anything to the bottom half of the house.

The average home has hundreds of places where air leaks out.  How do you decide which holes are more important to seal than others?  Well, the amount of air going through a hole depends on two things—the size of the hole and the amount of pressure difference on each side of the hole.  The warm air that rises in your home creates positive pressure pushing air out the holes at the top.  New air leaks into your home at the bottom due to the negative pressure caused by the air leaking out of the top.  And somewhere in the middle, there is a place where there is no pressure—the “neutral pressure plane.”

If you were to drill a hole in the wall at the exact point of the neutral pressure plane, air would leak neither in or out because there is no pressure pushing the air one way or the other.  The farther the leaks get from the neutral pressure plane, the more pressure there is, and the more air leaks in or out.  So sealing holes at the very top and bottom of your home are much more important than sealing the same sized hole near the middle.  Reducing the number of leaks at the top and bottom of your home will reduce drafts and overall air leakage and improve the comfort of your home.  And that is the best way to beat The Stack Effect.

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