Air distribution · Duct sizing
What duct size for 2,000 CFM?
2,000 CFM needs a 20-inch round duct at the standard 0.10 in/100 ft friction rate — the exact diameter works out to 18.1 in, at 917 fpm. For long or quiet runs, step up to 22 inches.
Size by design friction rate
| Friction (in/100 ft) | Exact ⌀ | Standard size | Velocity (fpm) |
|---|---|---|---|
| 0.05 | 20.7 in | 22 in | 758 |
| 0.08 | 18.9 in | 20 in | 917 |
| 0.10 | 18.1 in | 20 in | 917 |
| 0.15 | 16.7 in | 18 in | 1,132 |
Rectangular options
Rectangular ducts equivalent to the 18.1-inch round requirement. Only buildable shapes are listed — nothing narrower than 4 inches or beyond a 4:1 aspect ratio.
| Duct size | Equivalent ⌀ |
|---|---|
| 30 × 10 in | 18.3 in |
| 24 × 12 in | 18.3 in |
FAQ
- What size duct do I need for 2,000 CFM?
- A 20-inch round duct at the standard 0.10 in. w.c. per 100 ft friction rate — the exact calculated diameter is 18.1 in, and the next standard size up is 20 in. Air moves through it at 917 fpm.
- What if the run is long or noise matters?
- Design at a lower friction rate. At 0.05 in/100 ft the same 2,000 CFM needs a 22-inch duct — larger, but quieter and with less pressure loss over a long run.
- How many tons of cooling is 2,000 CFM?
- At the standard 400 CFM per ton, 2,000 CFM corresponds to about 5 tons. Humid climates design closer to 350 CFM per ton, dry climates up to 450.
Other airflows: 1,600 CFM · 2,500 CFM · any airflow · standard sizes