Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

# 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.

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 q1.9 / de5.02                               (1)

where

Δh = friction or head 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 head loss calculator below is based on formula (1):

Air Volume Flow - q - (cfm)

Equivalent duct diameter - de - (inches)

Duct Length - (feet)

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)
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 Volume Flow - q - (m3/s)

Equivalent duct diameter - de - (m)

Duct Length - (m)

### 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).

Air Duct Velocity

## Related Topics

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

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro .Add the Engineering ToolBox extension to your SketchUp from the SketchUp Pro Sketchup Extension Warehouse!

Translate

## Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

## Citation

• Engineering ToolBox, (2003). Air Ducts - Major Friction Head Loss, Online Calculator. [online] Available at: https://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html [Accessed Day Mo. Year].

Modify access date.

. .

close

3 10