Allowable Velocity in Ventilation Ducts

For a given airflow rate, the smaller the duct cross‑section, the higher the air velocity and consequently the greater the noise generated. Conversely, increasing the duct size reduces air velocity, which may compromise proper air delivery. Therefore, an optimal velocity must be determined—one that is not so low as to hinder airflow, nor so high as to produce excessive noise that disrupts occupant comfort. Naturally, these acceptable velocity and noise levels vary depending on the building type and its specific use.

Permissible air velocities in supply and return ducts (in fpm) based on building application are obtained from the table below: