Friction loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - imperial and SI units
The major loss, or friction loss, in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed
Δp = (0.109136 q1.9) / de5.02 (1)
Δp = friction (head or pressure loss) (inches water gauge/100 ft of duct)
de = equivalent duct diameter (inches)
q = air volume flow - (cfm - cubic feet per minute)
For rectangular ducts the equivalent diameter must be calculated.
Air Ducts Friction Loss Calculator - Imperial Units
The friction loss calculator below is based on formula (1):
Pressure loss and air flow velocity for some common duct sizes and air flow volumes can be taken from the table below:
|Pressure Loss (inches water gauge per 100 feet duct)|
|Air velocity (ft/min)|
|Air Volume |
|Duct Size (inches)|
Air velocity should not exceed certain limits to avoid unacceptable noise generation.
Air Ducts Friction Loss Calculator - SI Units
The friction loss calculator is based on formula (1) with input and output values modified for SI units.
Air Ducts - Velocity and Friction Loss - Excel Template
This Excel template can be use to calculate velocity and friction loss in air ducts.