ACCA Manual D • 0.1 in. wg Friction1600 CFM • 4 TonsStandard Residential (<900 FPM)
1,600 CFM Duct Size: 4.0 Ton HVAC Main Supply Trunk
Calculated duct sizing specifications for 1600 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 Size16" RoundSpiral / Snaplock Pipe
Air Velocity1146 FPMFeet Per Minute
Cooling Tonnage4 Tons@ 400 CFM / Ton
Register / Grille14x24Face Dimension
Equivalent Rectangular Duct Sizing Schedule
Exact rectangular sheet metal dimensions offering equivalent airflow resistance to a 16" round pipe
| Height (Depth) | Width | Cross Area | Air Velocity | Aspect Ratio | SMACNA Status |
|---|---|---|---|---|---|
| 12" Deep | 26" Wide | 312 sq in | 738 FPM | 2.2:1 | Optimal (<2:1) |
| 14" Deep | 22" Wide | 308 sq in | 748 FPM | 1.6:1 | Optimal (<2:1) |
Air Terminal & Grille Sizing Guidelines
Recommended face velocities to prevent whistling diffuser vanes
Supply Register Specifications
Recommended Grille Size:14x24 Supply Plaque / Dual 16x25 Return Grilles
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 4.0-ton AC moves 1,600 CFM. A single 16-inch round duct is tight; 18-inch round or 12x26 rectangular ducting is recommended to prevent static pressure choking.
- Return air must be sized with equal care: 4 tons of air requires dual return air drops or a 20x25 high-capacity media filter.
Frequently Asked Duct Sizing Questions
What duct size is required for a 4-ton system?
A 4-ton system (1,600 CFM) requires an 18-inch round duct or a 12x26 rectangular trunk.