Duct & Airflow Design Planner
Size a preliminary duct section and quantify velocity, friction loss and local resistance with transparent assumptions.
Screening range only. Starting values 2–12 m/s match this tool’s existing velocity warnings. They are not a cited code limit, and they do not change the pressure-drop result.
Engineering use case
For a 1.0 m³/s supply branch, compare a 500 mm round duct with a rectangular alternative. Use the resulting velocity and pressure drop to screen fan static pressure and identify sections that need a larger cross-section.
Method & limitations
Method: continuity V̇/A, hydraulic diameter 4A/P, Darcy–Weisbach Δp=f(L/Dh)ρV²/2, Blasius/Haaland-style turbulent correlation, and local loss Δp=KρV²/2. The screening velocity range is a warning only and does not change those formulas. Preliminary sizing only. The calculated velocity is not a recommended design size.
Formulas, source and scope
Formula source: site methodology / engineering assumption in this repository. No standard edition is pinned for this tool.
FAQ
What does the 1.0 m³/s, 500 mm example check?
It is a screening case for velocity and pressure drop, not a finished duct design. The velocity is flow divided by the entered area, about 5.09 m/s, and is not a recommended design size. The page starts with a 2–12 m/s screening range that you can edit; leaving that range adds a warning and does not change the pressure drop.
Which friction factor does the engine use?
Laminar 64/Re below Re 2300; 0.3164/Re^0.25 below Re 100,000; otherwise the Haaland-style expression written in the duct engine. Defaults are ε = 0.00015 m, ρ = 1.2 kg/m³, μ = 1.81e-5 Pa·s unless you override them in the engine input.