HVAC/R AI Pro
Duct sizing
HVAC Field Guide
How to size ductwork correctly
Correct duct sizing keeps airflow, noise, comfort, and equipment performance in balance. Poor sizing can make good equipment perform badly.
Field workflow
What this guide covers.
Learn how to size ductwork correctly using airflow requirements, static pressure, friction rate, and practical HVAC design principles.
Start with airflow
Duct sizing starts with the required CFM for the space and system. Guessing from old duct sizes can repeat the same performance problems.
Account for resistance
Friction rate, effective length, fittings, filters, coils, and layout restrictions all affect the duct size needed to move air properly.
Avoid common mistakes
Undersized ducts raise static pressure and reduce airflow, while oversized runs can reduce velocity and create comfort issues. Use real measurements and manufacturer data when possible.