Flexible Duct Calculator

Based on Friction Loss:

  • Enter Friction Loss (inches of water), Duct Airflow (CFM), Duct Length  and the number of bends.
  • Read Duct Diameter (inches) and Duct Velocity (FPM).

Based on Duct Diameter:

  • Enter Round Duct Diameter (inches), Duct Airflow (CFM), Duct Length and the number of bends.
  • Read Friction Loss (inches of water) and Duct Velocity (FPM).

Equivalent Rectangular Duct:

  • Enter Round Duct Diameter.
  • Enter the Desired Length of the Rectangular Duct.

Equivalent Round Duct Diameter:

  • Enter the Length of the Rectangular Duct.
  • Enter the Width of the Rectangular Duct.

Maximum Recommended Supply Velocity:

Foot per Minutes
Main Duct
Branch Duct
Residential
9000
600
Commercial
1300
900
Industrial
1800
1000

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