In winter, warm indoor air is lighter than cold outdoor air, so a tall building acts like a chimney: pressure is positive near the top and negative near the bottom, with a neutral plane in between. That drives infiltration at lobbies and lower floors and exfiltration at the top. Stack effect makes elevator doors whistle and lobby doors hard to open in tall buildings, and it reverses weakly in cooled buildings in summer.
Stack effect is so strong on cold days you can barely pull the lobby doors open, and the top floors are roasting.
Also heard as
- chimney effect
Related terms
Infiltration
Outdoor air that sneaks into a building through gaps in its shell, pushed by wind, stack effect and fans rather than by design.
Building pressurization
Controlling the air pressure inside a building relative to outdoors, usually by bringing in more outdoor air than is exhausted.
Building envelope
The walls, roof, floor, windows and doors that keep conditioned indoor space apart from the outdoors.