Hood Airflow Requirement Calculator

Work out hood airflow requirement instantly with clear inputs, formula shown and shareable results.

About Hood Airflow Requirement Calculator

For an enclosing hood, airflow is simply face area times the required face velocity, typically 0.5 m/s for a fume cupboard and up to 1.0 m/s for open booths. The connecting duct is then sized on transport velocity, which must be high enough to keep dust and mist entrained, usually 10 to 20 m/s.

Formulas

Hood airflow

Q = face area x face velocity

Duct size

Duct area = Q / duct velocity; diameter = sqrt(4A / pi)

Worked example

With the default values below, Hood Airflow Requirement Calculator returns Hood airflow required of 0.3600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hood widthminimum 0.05 m: 1.2 m
Hood opening heightminimum 0.05 m: 0.6 m
Required face velocityminimum 0.05 m/s: 0.5 m/s
Design duct velocityminimum 1 m/s: 10 m/s

Results

Hood airflow required: 0.3600 m³/s
Airflow in cubic feet per minute: 763 CFM
Hood face area: 0.720 m²
Duct diameter required: 214.1 mm

Step by step

1Values used
2Hood airflow
3Duct size
4Hood airflow required= 0.3600 m³/s
5Airflow in cubic feet per minute= 763 CFM
6Hood face area= 0.720 m²
7Duct diameter required= 214.1 mm

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 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Hood and duct design must follow a recognised industrial ventilation standard and be verified by measurement on commissioning.

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

Preliminary estimate only. Hood and duct design must follow a recognised industrial ventilation standard and be verified by measurement on commissioning.

Frequently Asked Questions

How is the Hood Airflow Requirement figure worked out?

Q = face area x face velocity. For an enclosing hood, airflow is simply face area times the required face velocity, typically 0.5 m/s for a fume cupboard and up to 1.0 m/s for open booths.

Why is duct velocity so much higher than face velocity?

Face velocity only has to capture contaminant at the opening. Duct velocity must keep particles suspended along the whole run, otherwise dust settles and eventually blocks the duct.

What values do I need to enter?

This calculator takes 4 inputs: Hood width, Hood opening height, Required face velocity, Design duct velocity. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.