Glossary · Testing & air leaks
Stack effect
Also called: chimney effect · stack pressure · thermal buoyancy
Warm indoor air rises and escapes near the top of a house, pulling cold outside air in near the bottom; it's strongest on cold days.
What it means
Warm air is lighter than cold air, so in winter it pushes out through leaks in upper floors and the attic while replacement air is drawn in through the basement and lower floors, including the rim joist area. The bigger the indoor-outdoor temperature difference, the taller the house and the leakier it is, the stronger the effect.
Why it matters in an audit
It explains why sealing the attic and basement matters most, why upper floors feel stuffy and lower floors drafty, and why radon tends to be higher in the colder months.