ACCA Manual D • 0.08 in. wg Friction200 CFM • 0.5 TonsWhisper Quiet (<700 FPM)
200 CFM Duct Size: Large Master Bedroom / Open Bonus Room
Calculated duct sizing specifications for 200 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 Size7" RoundSpiral / Snaplock Pipe
Air Velocity748 FPMFeet Per Minute
Cooling Tonnage0.5 Tons@ 400 CFM / Ton
Register / Grille6x12Face Dimension
Equivalent Rectangular Duct Sizing Schedule
Exact rectangular sheet metal dimensions offering equivalent airflow resistance to a 7" round pipe
| Height (Depth) | Width | Cross Area | Air Velocity | Aspect Ratio | SMACNA Status |
|---|---|---|---|---|---|
| 6" Deep | 10" Wide | 60 sq in | 480 FPM | 1.7:1 | Optimal (<2:1) |
| 8" Deep | 8" Wide | 64 sq in | 450 FPM | 1.0:1 | Optimal (<2:1) |
Air Terminal & Grille Sizing Guidelines
Recommended face velocities to prevent whistling diffuser vanes
Supply Register Specifications
Recommended Grille Size:6x12 or 4x14 Supply Register
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 7-inch round metal pipe or 8-inch flex duct delivers 200 CFM smoothly with minimal friction loss.
- Where 7-inch pipe is unavailable locally, use an 8-inch round duct with a manual balancing damper at the takeoff collar.
Frequently Asked Duct Sizing Questions
What size duct delivers 200 CFM?
A 7-inch round metal duct or an 8-inch round flex duct is ideal for 200 CFM (equivalent to 0.5 tons of cooling capacity).