Ventilation ducts are selected based on velocity criteria.

Unit resistance in Pa/m is calculated using the Darcy-Weisbach formula. Absolute roughness is assumed for galvanized steel.

The provided selections should be analyzed by the designer and adjusted according to the specific project situation.

Velocity criterion for duct selection is 5.5 m/s

Recommended air velocity at intake not more than 2.5 m/s

Recommended air velocity at outlet not more than 4.0 m/s

For ducts in industrial facilities, air velocities can be higher, in the range of 6-10 m/s

For ducts at diffusers, lower velocities of 3-4 m/s are recommended