Chart
Duct velocity chart
Air velocity decides whether a duct is quiet and efficient or loud and starved. This chart shows the velocity for round duct at a given size and airflow, so you can keep a run inside the comfortable range for its job.
| CFM \ size | 8" | 10" | 12" | 14" | 16" |
|---|---|---|---|---|---|
| 200 | 573 | 367 | 255 | 187 | 143 |
| 400 | 1,146 | 733 | 509 | 374 | 286 |
| 800 | 2,292 | 1,467 | 1,019 | 748 | 573 |
| 1,200 | 3,438 | 2,200 | 1,528 | 1,123 | 859 |
For any size or airflow, the console returns the exact velocity along with the round, rectangular, and flat-oval sizes.
Recommended velocity ranges
Common guidance keeps residential supply trunks around 700–900 feet per minute, with branches and returns a step slower to stay quiet; light commercial supply often runs 1,200–1,500 feet per minute. Higher velocity packs the same air into a smaller duct, but at the cost of more noise and static pressure — and, past a point, an undersized run the blower can't overcome.
Velocity, size, and airflow are locked together by
velocity = 183.3 · CFM / D²,
so doubling the airflow through the same duct doubles the velocity. To size from
a velocity target instead of reading the chart, use the
CFM-to-duct-size
chart or the console, which
also flags when a result runs too fast for its application.