HVAC · Air side
800 CFM needs a 14 in round duct
At the common 0.08 in. wc per 100 ft residential friction rate, galvanized steel, standard air. Every number here is computed from the ASHRAE / Manual D equal-friction duct model on each build, not looked up.
800 CFM duct sizing (0.08 in. wc/100 ft)
| Property | Value |
|---|---|
| Airflow | 800 CFM |
| Round size | 14 in |
| Velocity | 748 fpm |
| Friction | 0.059 in. wc/100 ft |
| Rectangular equivalents | 22×8, 18×10, 14×12 |
These are static reference figures at the residential design rate. For your own airflow and friction rate, run the interactive duct size calculator, or convert a shape with the round-to-rectangular converter.
FAQs
What size duct do I need for 800 CFM?
800 CFM needs a 14 in round duct at the common 0.08 in. wc per 100 ft friction rate (galvanized steel, standard air). That runs at about 748 fpm. Rectangular equivalents that carry the same airflow at the same friction are 22 by 8 in, 18 by 10 in, 14 by 12 in.
What is the rectangular equivalent for 800 CFM?
22 by 8 in, 18 by 10 in, 14 by 12 in all share the equivalent diameter of the 14 in round, so they move 800 CFM at the same friction. Use the round-to-rectangular converter to match any depth your space allows.
What friction rate is this based on?
0.08 in. wc per 100 ft, the standard residential design target that ACCA Manual D Appendix 3 tables assume. At a looser 0.10 in. wc per 100 ft you can often drop a size; your own rate is available static pressure times 100 divided by total effective length.