The stack effect describes the natural movement of air through a building due to temperature and pressure differences between interior and exterior spaces. Warm air rises and escapes through upper openings while cooler air enters through lower openings, creating a vertical air circulation pattern. This effect increases energy loss and can account for 20-40 percent of uncontrolled air leakage in older buildings.
Physical Mechanism
The stack effect occurs when interior air is warmed, becomes less dense, and rises toward the ceiling. As this air escapes through upper cracks, openings, or unsealed penetrations, pressure inside the building decreases, drawing cooler exterior air in through lower gaps and openings. The greater the temperature difference between inside and outside, the stronger the stack effect becomes.
Control and Mitigation
Sealing air leaks at the top and bottom of the thermal envelope, maintaining balanced ventilation systems, and proper ductwork sealing reduce stack effect losses. Weatherstripping, caulking, and air barrier materials effectively minimize uncontrolled air movement.