ACCA Manual D • 0.1 in. wg Friction1000 CFM • 2.5 TonsWhisper Quiet (<700 FPM)
1,000 CFM Duct Size: 2.5 Ton HVAC Main Trunk Line
Calculated duct sizing specifications for 1000 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 Size14" RoundSpiral / Snaplock Pipe
Air Velocity935 FPMFeet Per Minute
Cooling Tonnage2.5 Tons@ 400 CFM / Ton
Register / Grille10x22Face Dimension
Equivalent Rectangular Duct Sizing Schedule
Exact rectangular sheet metal dimensions offering equivalent airflow resistance to a 14" round pipe
| Height (Depth) | Width | Cross Area | Air Velocity | Aspect Ratio | SMACNA Status |
|---|---|---|---|---|---|
| 8" Deep | 26" Wide | 208 sq in | 692 FPM | 3.3:1 | Acceptable (<3:1) |
| 10" Deep | 20" Wide | 200 sq in | 720 FPM | 2.0:1 | Optimal (<2:1) |
| 12" Deep | 18" Wide | 216 sq in | 667 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:10x22 Supply Trunk / 20x20 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 14-inch round metal duct or 10x20 rectangular duct is the industry benchmark for 2.5 tons (1,000 CFM).
- Maintain an aspect ratio under 3:1 on rectangular ductwork to prevent excessive friction loss and turbulence.
Frequently Asked Duct Sizing Questions
What size duct is required for 1,000 CFM?
A 14-inch round duct or a 10x20 rectangular sheet metal trunk is recommended for 1,000 CFM.