Stack Effect
The stack effect is the natural draught created when warm, less dense air or gas rises through a vertical flue or building, drawing cooler air in at the bottom. It drives chimney draught and influences building ventilation and heat loss.
Buoyancy makes hot gas rise: in a chimney this self-induced draught pulls combustion air through a burner without a fan, and in a tall building it drives air upward and out through the top while cold air infiltrates lower floors. The driving force grows with stack height and the temperature difference between inside and outside. The stack effect helps natural-draught burners but also causes uncontrolled infiltration and heat loss in poorly sealed buildings.