The Importance of Proper Duct Design

The air duct network is the main artery for distributing conditioned air. Incorrect design leads to high noise, unbalanced air distribution, and high operating costs.

Equal Friction Method

The most commonly used method in commercial design. It relies on selecting a constant friction rate (typically 0.8 – 1.0 Pa/m) for all sections of the network.


Metal air duct network installed in the ceiling of a commercial building

Design Steps

  1. Determine the airflow rate for each space (m³/h)
  2. Draw the network map and identify the critical path
  3. Select duct dimensions from a Friction Chart
  4. Calculate the total pressure drop for the critical path
  5. Select the fan based on: flow rate + total pressure + efficiency

Recommended Air Velocities

Duct Location Recommended Velocity
Main Duct 5 – 8 m/s
Branch Ducts 3 – 5 m/s
At Outlets (Diffusers) 1.5 – 3 m/s