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Friction Head Loss in Air Ducts - 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):

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)
Air velocity (ft/min)
Air Volume (cfm)	Duct Size (inches)
Air Volume (cfm)	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.

Pressure vs. head

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

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Air Ducts - Friction Loss Diagram - Major loss diagram for air ducts - SI units
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Tag Search

en: air ducts head friction pressure loss rectangular circular

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