Air distribution · Duct sizing
What duct size for 1,600 CFM?
1,600 CFM needs a 18-inch round duct at the standard 0.10 in/100 ft friction rate — the exact diameter works out to 16.6 in, at 905 fpm. For long or quiet runs, step up to 20 inches.
Size by design friction rate
| Friction (in/100 ft) | Exact ⌀ | Standard size | Velocity (fpm) |
|---|---|---|---|
| 0.05 | 19.1 in | 20 in | 733 |
| 0.08 | 17.4 in | 18 in | 905 |
| 0.10 | 16.6 in | 18 in | 905 |
| 0.15 | 15.3 in | 16 in | 1,146 |
Rectangular options
Rectangular ducts equivalent to the 16.6-inch round requirement. Only buildable shapes are listed — nothing narrower than 4 inches or beyond a 4:1 aspect ratio.
| Duct size | Equivalent ⌀ |
|---|---|
| 25 × 10 in | 16.9 in |
| 20 × 12 in | 16.8 in |
FAQ
- What size duct do I need for 1,600 CFM?
- A 18-inch round duct at the standard 0.10 in. w.c. per 100 ft friction rate — the exact calculated diameter is 16.6 in, and the next standard size up is 18 in. Air moves through it at 905 fpm.
- What if the run is long or noise matters?
- Design at a lower friction rate. At 0.05 in/100 ft the same 1,600 CFM needs a 20-inch duct — larger, but quieter and with less pressure loss over a long run.
- How many tons of cooling is 1,600 CFM?
- At the standard 400 CFM per ton, 1,600 CFM corresponds to about 4 tons. Humid climates design closer to 350 CFM per ton, dry climates up to 450.
Other airflows: 1,400 CFM · 2,000 CFM · any airflow · standard sizes