Smoke Control Airflow Calculator

Work out smoke control airflow instantly with clear inputs, formula shown and shareable results.

About Smoke Control Airflow Calculator

Smoke control fans move hot gas, which occupies far more volume than the same mass of cool air. The cold air flow needed to hold a design velocity through the opening is area times velocity, and multiplying by the ratio of absolute temperatures gives the volumetric rate the fan must actually handle: at 300 °C that is nearly double.

Formulas

Cold flow

Q cold = opening area x design velocity

Hot flow

Q hot = Q cold x (T smoke + 273) / (T ambient + 273)

Worked example

With the default values below, Smoke Control Airflow Calculator returns Hot smoke extract rate required of 3.910. Change any input above and every figure here is recalculated in your browser.

Inputs used

Opening area to be protectedminimum 0.01 m²: 2 m²
Design air velocity through the openingminimum 0.1 m/s: 1 m/s
Smoke layer temperatureminimum 20 °C: 300 °C
Ambient temperatureminimum -20 °C: 20 °C

Results

Hot smoke extract rate required: 3.910 m³/s
Equivalent cold air flow: 2.000 m³/s
Extract rate per hour: 14,077 m³/h
Thermal expansion ratio: 1.955

Step by step

1Values used
2Cold flow
3Hot flow
4Hot smoke extract rate required= 3.910 m³/s
5Equivalent cold air flow= 2.000 m³/s
6Extract rate per hour= 14,077 m³/h
7Thermal expansion ratio= 1.955

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Smoke control design must be carried out by a qualified fire engineer using recognised plume and layer models.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Smoke control design must be carried out by a qualified fire engineer using recognised plume and layer models.

Frequently Asked Questions

How is the Smoke Control Airflow figure worked out?

Q cold = opening area x design velocity. Smoke control fans move hot gas, which occupies far more volume than the same mass of cool air.

Why does the fan have to be rated for temperature?

It handles the hot gas directly. Smoke extract fans are certified for continuous operation at elevated temperature, typically 300 °C for two hours or 400 °C for one hour.

What values do I need to enter?

This calculator takes 4 inputs: Opening area to be protected, Design air velocity through the opening, Smoke layer temperature, Ambient temperature. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.