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Duct Pressure Drop Calculator
Calculate the friction pressure drop in ductwork. Enter the airflow, duct diameter, and total length to determine the pressure loss the fan must overcome.
Duct Pressure Drop Explained
As air flows through a duct, friction between the air and duct walls causes a pressure drop. The pressure drop per metre depends on the air velocity, duct diameter, and surface roughness.
For system design, the total pressure drop is the sum of straight-run friction losses plus fitting losses (elbows, transitions, branches, grilles). Fitting losses are often expressed as equivalent lengths of straight duct.
Frequently Asked Questions
What is an acceptable duct pressure drop?
Typically 1–3 Pa/m for low-pressure residential systems and 3–8 Pa/m for medium-pressure commercial systems. Total system pressure drop should be within the fan's rated static pressure.
How do I reduce duct pressure drop?
Use larger duct diameters, minimise elbows and transitions, use smooth-radius bends, and keep velocities moderate (3–5 m/s). Each fitting adds equivalent length pressure loss.
Duct Pressure Drop Calculator
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