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Air Ducts - Major Friction Head Loss, Online Calculator

Head loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - Imperial and SI units.

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The major loss, or friction loss, in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed

Δh= 0.109136 q^1.9 / d_e^5.02 (1)

where

Δh = friction or head loss (inches water gauge/100 ft of duct)

d_e = equivalent duct diameter (inches)

q = air volume flow - (cfm - cubic feet per minute)

For rectangular ducts the equivalent diameter must be calculated.

Pressure vs. head

Air Ducts Friction Loss Calculator - Imperial Units

The head loss calculator below is based on formula (1):

Air Volume Flow - q - (cfm)

Equivalent duct diameter - d_e - (inches)

Duct Length - (feet)

Load Calculator!

Head loss and air flow velocity for some common duct sizes and air flow volumes can be taken from the table below:

Head Loss (inches water gauge per 100 feet duct) Load Calculator!
Air velocity (ft/min) Load Calculator!
Air Volume (cfm) Load Calculator!	Duct Size (inches)
Air Volume (cfm) Load Calculator!	4	5	6	8	10	12	16
100	0.65	0.21	0.09	0.02	0.01
100	1146	733	509	286	183
200		0.8	0.32	0.08	0.02	0.01
200		1467	1019	573	367	255
400			1.19	0.28	0.09	0.04	0.01
400			2037	1146	733	509	286
800					0.34	0.14	0.03
800					1467	1019	573
1600							0.12
1600							1146

Air velocity should not exceed certain limits to avoid unacceptable noise generation.

Air Ducts Friction Loss Calculator - SI Units

This pressure loss calculator is based on formula (1) with input and output values modified for SI units.

Air Volume Flow - q - (m³/s)

Equivalent duct diameter - d_e - (m)

Duct Length - (m)

Load Calculator!

Pressure vs. head

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Air Ducts - Velocity and Friction Loss - Excel Template

This Excel template can be used to calculate velocity and friction loss in air ducts.

Air Ducts - Friction Loss Diagram

The chart below can be used to estimate friction loss in air ducts.

The default values are for air flow 400 cfm (680 m³/h), duct size 8 in (200 mm) and friction loss 0.28 inH2O/100ft (2.3 Pa/m).

Download and print Air Ducts Friction Loss Diagram!

Air Duct Velocity

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Related Topics

Ventilation - Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

Related Documents

Air Duct Velocities - Typical air duct velocities in applications like ventilation systems or compressed air systems.
Air Ducts - Friction Loss Diagram - A major friction loss diagram for air ducts - SI units.
Air Ducts - Friction Loss Diagram - A major friction loss diagram for air ducts - Imperial units ranging 10 - 100 000 cfm.
Air Ducts - Velocity Diagram - Air flow volume, duct size, velocity and dynamic pressure.
Duct Sizing - the Equal Friction Method - The equal friction method for sizing air ducts is easy and straightforward to use.
Duct Systems - Pressure Classifications - Duct systems are commonly divided into three pressure classifications.
Duct Velocity - Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator.
Ducts Sizing - the Velocity Reduction Method - The velocity reduction method can be used when sizing air ducts.
Ductwork - Seal Classes - Ductwork air leakage classes.
Equivalent Diameter - Rectangular vs. Circular HVAC Ducts - Rectangular equivalent diameter for air flows between 100 - 50000 cfm.
Fluid Flow - Equivalent Diameter - Convert rectangular and oval duct geometry to a equivalent circular diameter - online calculator with imperial and SI-units.
Fluid Flow - Hydraulic Diameter - Calculate hydraulic diameter for pipes and ducts.
Sizing Circular Ducts - A rough guide to maximum air volume capacity of circular ducts in comfort, industrial and high speed ventilation systems.
Spiral Ducts - Dimensions - Standard dimensions of spiral ducts - Imperial units.
Velocity Classification of Ventilation Ducts - Recommended air velocities in ventilation ducts

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