About The Duct Friction Rate Calculator

The Duct Friction Rate Calculator estimates air velocity, Reynolds number, Darcy friction factor, and pressure loss per meter for a circular equivalent duct. It is useful for early HVAC duct sizing when airflow, equivalent diameter, roughness, and air density are known.

How to Use the Duct Friction Rate Calculator Online

1. Enter the airflow in m^3/h.
2. Enter the equivalent duct diameter in millimeters.
3. Set the absolute roughness and air density for the duct and operating condition.
4. Run the calculation and review velocity, flow regime, friction factor, and friction rate.

Choosing Options Correctly

Use an equivalent diameter when adapting rectangular ductwork to this simplified circular model. Keep roughness in millimeters and density in kg/m^3 so the Pa/m result remains consistent.

Common Use Cases

• Estimate duct friction rate during preliminary HVAC layout.
• Compare airflow impact across alternate duct sizes.
• Provide pressure-loss inputs for fan static pressure checks.

Quick FAQ

What is duct friction rate?
It is the pressure loss per unit duct length caused by air moving through the duct.

Does this include fittings?
No. Elbows, transitions, dampers, coils, filters, and diffusers add separate pressure losses.

Why does duct size matter?
Smaller ducts raise velocity and friction, which can increase fan power and noise.

Can this size a full duct system?
No. Full duct design needs layout, fittings, balancing, acoustics, and fan static pressure checks.