Duct Components
The straight-run pieces that carry the flow.
What a Duct Component Is
A Duct component is one straight run of duct: a single piece with a constant cross-section carrying a known airflow. You chain duct components (with elbows, tees, and transitions between them) from the fan to each terminal. Each one contributes straight-run friction loss, and its length feeds the fittings around it.
Duct Inputs
Length
The straight-run length in feet. Do not include equivalent lengths for fittings. DuctStatic calculates fitting losses directly from loss coefficients, not equivalent lengths.
Duct Shape
Round: Enter the inside diameter in inches.
Rectangular: Enter width and height in inches. The calculator uses hydraulic diameter internally: Dh = 2WH / (W+H)
These inputs use the default English view (feet, inches); the header toggle switches the form to SI (m, mm).
Material
Select the duct material. This determines the absolute roughness used in the friction factor calculation (you can override ε with a custom value if needed).
- Galvanized steel (spiral/seam). Roughness of approximately 0.09 mm. The default for most commercial HVAC.
- Galvanized steel (longitudinal seam). Slightly higher roughness.
- Flexible duct. Significantly higher roughness. Expect considerably more friction loss per foot.
- Fiberglass duct board. Intermediate roughness.
- Smooth (aluminum, PVC). Lowest roughness.
Material also drives the acoustics: flexible duct attenuates sound more than unlined sheet metal, and an internally lined duct adds the absorption of acoustical lining per octave band. See Calculation Method → Sound.
How Friction Loss is Calculated
For each duct run, DuctStatic computes:
- Air velocity from flow and cross-sectional area
- Reynolds number from velocity, hydraulic diameter, air density, and viscosity
- Darcy friction factor via the Colebrook-White equation (iterative Newton-Raphson; laminar flow uses
f = 64/Re) - Friction loss:
ΔP = f × (L/Dh) × (ρV²/2)
See Calculation Method for the full explanation.