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Ductulator
ASHRAE equal-friction duct sizing for field reference.
What is the supply airflow (CFM)?
1200CFM
Total supply cubic feet per minute from the air handler.
Target friction rate (optional)
0.08in. wg/100 ft
Industry standard: 0.08-0.10 in. wg/100 ft for supply ducts.
Target velocity (optional)
800FPM
Supply ducts: 700-900 FPM optimal, 600-700 FPM for return.
ROUND DUCT SOLUTION
20.00"
Diameter
4
FPM
1.79
Friction (in.wg/100ft)
Velocity too low
Increase duct size to reduce staticRECTANGULAR OPTIONS
2.0" x 0.5"
Area: 1.0 sq in
1200 FPM
De: 1.03"
1.5" x 1.0"
Area: 1.5 sq in
800 FPM
De: 1.33"
1.5" x 1.0"
Area: 1.5 sq in
800 FPM
De: 1.33"
1.0" x 1.0"
Area: 1.0 sq in
1200 FPM
De: 1.09"
De = equivalent diameter for friction lookup. Width x Height should match available ductwork stock.
Flex Duct Equivalent
18.5"
Conservative 1.5" reduction for friction loss. Verify actual flex ductwork friction data.
For reference; verify against project design. This calculator uses standard ASHRAE equal-friction sizing. Actual duct design must account for system static pressure, fittings, length, and local code. Always confirm final duct size and layout with a licensed HVAC designer or engineer.
Tip: Tap the browser print button (or Cmd/Ctrl+P) to save this calculation as a PDF field reference card.