Buildtech

Fabric Air Duct (Textile Air Dispersion) Sizing: Diameter, Velocity, Fabric Area, Mass & Hangers

Ten thousand cubic metres an hour at six metres a second needs a duct close to 800 mm across, and every metre of it is two and a half square metres of fabric.

Air From the ventilation design
m³/h
m/s

The velocity your design or the duct maker allows at the inlet; it sets noise and pressure.

mm

Diameters come in steps; the computed size is rounded up to the next one.

Duct From the layout and the fabric
m
%
g/m²
m

Duct Diameter

— mm

Computed from airflow and velocity, rounded up to the size step

Duct

Computed Diameter
— mm
Inlet Velocity in the Chosen Size
— m/s
Air Released per Metre (Even Spread)
— m³/h
Fabric incl. Seams
— m²
Fabric Mass
— kg
Suspension Points
— points

The diameter follows from continuity: airflow equals area times velocity. The design velocity, size step, seams allowance and hanger spacing are yours or the maker's; the tool has no typical value for any of them. Air released per metre assumes the duct lets the air out evenly along its length, which is how most fabric ducts are specified; nozzles and orifices that throw air further are the maker's design. Mass is the fabric only; rails, cables and end caps are extra. **This is a sizing estimate: pressure, throw and comfort are checked by the duct maker's software for the room.**

Fabric Air Duct (Textile Air Dispersion) Sizing: Diameter, Velocity, Fabric Area, Mass & Hangers — free, with the formula and a worked example, at Textile School.