Stack effect is the movement of air into and out of buildings,
chimneys,
flue gas stacks, 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. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the "chimney effect", and it helps drive
natural ventilation,
infiltration, and fires (see
Kaprun disaster and
King's Cross fire).