Paritian

Engineering

Stack Effect Calculator (Chimney Effect in Buildings and Flues)

The pressure difference and the airflow that warm air rising in a building, stairwell or chimney creates between a low and a high opening, from the height and the two temperatures.

Results

Stack-effect pressure difference 7.2 Pa
Airflow driven by the stack effect 1.088 m³/s
The same airflow per hour 3916 m³/h
Air speed through the openings 2.18 m/s
How it changes
Stack-effect pressure differenceOutdoor air temperature -20 – 20. Stack-effect pressure difference: 15.2478 → 0.321152Stack-effect pressure difference05101520-20-1001020Outdoor air temperature (°C)

The dashed line marks the value you entered.

What this tool does

Warm air is lighter than cold, so in a tall space it rises and leaks out at the top while cold air is drawn in at the bottom — the stack, or chimney, effect. The pressure it creates is Δp = ρ_out × g × h × (1 − T_out ÷ T_in), with temperatures in kelvin: with 21 °C inside and 0 °C outside, every 10 m of height gives about 9 Pa. It is why lift shafts whistle in winter and why doors on the ground floor of a tall building are hard to open. The airflow formula assumes equal low and high openings and ignores wind and mechanical fans, which in real buildings often matter more.

Formula

Δp = ρ_out × g × h × (1 − T_out ÷ T_in) · Q = Cd × A × √(2 g h (T_in − T_out) ÷ T_in) (temperatures in kelvin)

Variables

SymbolMeaningUnit
hVertical distance between the lower and upper openingsm
tiIndoor air temperature°C
teOutdoor air temperature°C
aFree area of each opening (inlet and outlet equal)m²
cdDischarge coefficient Cd (about 0.65 for sharp-edged openings)—
DPStack-effect pressure differencePa
QAirflow driven by the stack effectm³/s
QHThe same airflow per hourm³/h
VAir speed through the openingsm/s

Worked example

  • Vertical distance between the lower and upper openings8 m
  • Indoor air temperature21 °C
  • Outdoor air temperature0 °C
  • Free area of each opening (inlet and outlet equal)0.5 m²
  • Discharge coefficient Cd (about 0.65 for sharp-edged openings)0.65
  • Stack-effect pressure difference7.2 Pa
  • Airflow driven by the stack effect1.088 m³/s
  • The same airflow per hour3916 m³/h
  • Air speed through the openings2.18 m/s

Limitations

  • The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
  • The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.