Duct Design Basics: Getting Airflow Right the First Time

A perfectly sized chiller or AHU can still deliver a disappointing result if the ductwork feeding it is undersized or poorly laid out. Duct design doesn't get the attention it deserves, but it's often the difference between a system that performs on paper and one that performs in the building.

The most common mistake is sizing ducts for a rough rule of thumb instead of actual calculated air volumes. Undersized ducts increase static pressure, force fans to work harder, raise noise levels, and quietly increase energy consumption for the life of the system.

Sharp bends and abrupt transitions are another frequent culprit — every 90-degree elbow and sudden reduction adds resistance that has to be accounted for in the fan selection, or you end up with rooms at the end of a duct run getting far less air than the ones near the AHU.

Material and insulation matter too. Poorly insulated ducts running through unconditioned spaces bleed cooling capacity before it even reaches the room, and leaky joints can waste a significant share of total airflow.

We follow SMACNA sizing standards on every project and pressure-test ductwork before handover, because a duct system is invisible once the ceiling goes up — but its effects are not.