ACCA Manual D • 0.08 in. wg Friction300 CFM • 0.75 TonsWhisper Quiet (<700 FPM)
10-Inch Flex Duct CFM Capacity & Sizing Guide
Calculated duct sizing specifications for 300 CFM of conditioned airflow. Sized via the Equal Friction Method and Huebscher equivalent rectangular equation to maintain static pressure and eliminate air rush noise.
Round Duct Size10" RoundSpiral / Snaplock Pipe
Air Velocity550 FPMFeet Per Minute
Cooling Tonnage0.75 Tons@ 400 CFM / Ton
Register / Grille8x14Face Dimension
Equivalent Rectangular Duct Sizing Schedule
Exact rectangular sheet metal dimensions offering equivalent airflow resistance to a 10" round pipe
| Height (Depth) | Width | Cross Area | Air Velocity | Aspect Ratio | SMACNA Status |
|---|---|---|---|---|---|
| 8" Deep | 12" Wide | 96 sq in | 450 FPM | 1.5:1 | Optimal (<2:1) |
Air Terminal & Grille Sizing Guidelines
Recommended face velocities to prevent whistling diffuser vanes
Supply Register Specifications
Recommended Grille Size:8x14 Register or 12x12 Return Grille
Maximum Target Velocity:500–700 FPM at register face
Diffuser Throw:Spread toward outside walls
Return Air Intake Rules
Return Velocity Target:<450 FPM through filter face
Filter Surface Requirement:Minimum 2 sq ft per Ton
Return Friction Target:0.05 – 0.08 in. wg / 100 ft
HVAC Sheet Metal & Installation Directives
- A 10-inch flex duct moves 300 CFM quietly at 550 FPM, making it the perfect feeder for two branched 6-inch bedroom runs via a wye splitter.
- Keep bends to a minimum bend radius of at least 1.0 times duct diameter (10-inch radius).
Frequently Asked Duct Sizing Questions
How many CFM can a 10-inch flex duct deliver?
A 10-inch flex duct delivers 280 to 350 CFM depending on friction rate and run length.