Air distribution · Duct sizing
What duct size for 3,000 CFM?
3,000 CFM needs a 22-inch round duct at the standard 0.10 in/100 ft friction rate — the exact diameter works out to 21.1 in, at 1,136 fpm. For long or quiet runs, step up to 26 inches.
Size by design friction rate
| Friction (in/100 ft) | Exact ⌀ | Standard size | Velocity (fpm) |
|---|---|---|---|
| 0.05 | 24.2 in | 26 in | 814 |
| 0.08 | 22 in | 24 in | 955 |
| 0.10 | 21.1 in | 22 in | 1,136 |
| 0.15 | 19.4 in | 20 in | 1,375 |
Rectangular options
Rectangular ducts equivalent to the 21.1-inch round requirement. Only buildable shapes are listed — nothing narrower than 4 inches or beyond a 4:1 aspect ratio.
| Duct size | Equivalent ⌀ |
|---|---|
| 33 × 12 in | 21.1 in |
FAQ
- What size duct do I need for 3,000 CFM?
- A 22-inch round duct at the standard 0.10 in. w.c. per 100 ft friction rate — the exact calculated diameter is 21.1 in, and the next standard size up is 22 in. Air moves through it at 1,136 fpm.
- What if the run is long or noise matters?
- Design at a lower friction rate. At 0.05 in/100 ft the same 3,000 CFM needs a 26-inch duct — larger, but quieter and with less pressure loss over a long run.
- How many tons of cooling is 3,000 CFM?
- At the standard 400 CFM per ton, 3,000 CFM corresponds to about 7.5 tons. Humid climates design closer to 350 CFM per ton, dry climates up to 450.
Other airflows: 2,500 CFM · 4,000 CFM · any airflow · standard sizes