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# Air Ducts - Major Friction Head Loss, Online Calculator

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.

### 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:

Air Ducts - Major Friction Head Loss
Air Volume
(cfm)

Head Loss (inches water gauge per 100 feet duct)
Air velocity (ft/min)
Duct Size (inches)
4568101216
100 0.65 0.21 0.09 0.02 0.01
1146 733 509 286 183
200 0.8 0.32 0.08 0.02 0.01
1467 1019 573 367 255
400 1.19 0.28 0.09 0.04 0.01
2037 1146 733 509 286
800 0.34 0.14 0.03
1467 1019 573
1600 0.12
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 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 m 3 /h) , duct size 8 in (200 mm) and friction loss 0.28 inH2O/100ft (2.3 Pa/m) .

Air Duct Velocity

## 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 - Imperial units ranging 10 - 100 000 cfm.

### Air Ducts - Friction Loss Diagram

A major friction loss diagram for air ducts - SI units.

### 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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