ENGINEERING – THERMODYNAMIC & HVAC CALCULATOR
Stack Draught
A precise tool.
What is the Stack Draught & How does it work?
The stack (or chimney) effect is a natural ventilation phenomenon that occurs when there is a temperature difference between the indoor and outdoor air. Warm air inside a building becomes less dense and rises, creating a pressure difference that drives airflow through openings. The magnitude of this pressure difference depends on the height of the vertical air column and the density contrast, which is directly related to the temperature difference. As the temperature difference increases, the density difference grows, enhancing the driving force for the draught. Engineers use the stackβdraught calculation to size vents, chimneys, and passive cooling devices. By estimating the pressure difference and resulting air velocity, designers can predict natural ventilation rates without mechanical assistance.
\Delta P = g ; H ; (\rho_{out} – \rho_{in})
ΞP = pressure difference (Pa); g = gravitational acceleration (9.81β―m/sΒ²); H = height of the vertical column (m); Ο = air density (kg/mΒ³)
Parameters
Result
β
Frequently Asked Questions
How does temperature difference affect stack draught?
The greater the temperature difference between indoor and outdoor air, the stronger the stack draught effect.
What is stack draught in engineering terms?
Stack draught refers to the natural airflow driven by the density difference of warm indoor air rising compared to cooler outdoor air.
Can you explain how stack height influences stack draught?
Higher stack heights increase the vertical air column, amplifying the stack draught effect for a given temperature difference.
What factors can reduce stack draught effectiveness?
Obstructions, wind direction, and insufficient opening sizes can all reduce the effectiveness of stack draught in ventilating a building.
How does stack draught contribute to energy efficiency?
Stack draught helps in naturally venting warm air out of buildings, reducing heating costs by allowing cooler outdoor air to enter.
Is stack draught the same as chimney draft?
Yes, stack draught and chimney draft are essentially the same phenomenon, describing natural airflow driven by temperature differences.
How can I calculate the pressure difference due to stack draught?
Use the formula ΞP = ΟgΞh, where ΞP is the pressure difference, Ο is the density difference of air, g is acceleration due to gravity, and Ξh is the height of the stack.
Results are for informational purposes only and do not constitute professional advice.