Air Duct Components - Minor Dynamic Loss Coefficients

Calculate minor or dynamic pressure losses in air duct systems caused by changes in air direction, restrictions, or velocity changes. Uses the formula: Δp_minor_loss = ξ ρ v² / 2

Component or Fitting	Minor Loss Coefficient (ξ)
90° bend, sharp	1.3
90° bend, with vanes	0.7
90° bend, rounded radius/diameter duct <1	0.5
90° bend, rounded radius/diameter duct >1	0.25
45° bend, sharp	0.5
45° bend, rounded radius/diameter duct <1	0.2
45° bend, rounded radius/diameter duct >1	0.05
T, flow to branch (applied to velocity in branch)	0.3
Flow from duct to room	1
Flow from room to duct	0.35
Reduction, tapered	0
Enlargement, abrupt	variable
Enlargement, tapered angle < 8°	variable
Enlargement, tapered angle > 8°	variable
Grilles, 0.7 ratio free area to total surface	3
Grilles, 0.6 ratio free area to total surface	4
Grilles, 0.5 ratio free area to total surface	6
Grilles, 0.4 ratio free area to total surface	10
Grilles, 0.3 ratio free area to total surface	20
Grilles, 0.2 ratio free area to total surface	50

Calculator

Inputs

Minor Loss Coefficient (ξ) (-)

Air Density (ρ) (kg/m³)

Air Velocity (v) (m/s)

Results

Minor Pressure Loss (Δp)-- Pa