# Duct Velocity

### Air Duct Velocity - Imperial Units

Air velocity in a ventilation duct can be calculated in imperial units as

v_{ i }= q_{ i }/ A_{ i }

= q_{ i }/ [ π (d_{ f }/ 2)^{ 2 })]

= q_{ i }/ [ π ((d_{ i }/ 12) / 2)^{ 2 })]

= (576 / π) ( q_{ i }/ d_{ i }^{ 2 })

= 144 q_{ i }/ (a_{ i }b_{ i }) (1)

where

v_{ i }= air velocity (ft/min)

q_{ i }= air flow (ft^{ 3 }/min)

A_{ i }= area of duct (ft^{ 2 })

d_{ f }= diameter of duct (ft)

d_{ i }= diameter of duct (in)

a_{ i }= width of duct (in)

b_{ i }= width of duct (in)

#### Example - Air Flow Velocity in a Duct

The velocity in a * 12 inch * duct with air flow * 1000 cfm * can be calculated as

* v _{ i } = (576 / π ) (1000 cfm) / (12 in) ^{ 2 } ) *

* = 1273 (ft/min) *

#### Air Flow Velocity Calculator - Imperial Units

Air velocity can be calculated with the calculator below. Add air volume - * q * - and diameter - * d * - (or length * a * and * b * ).

or alternatively

### Related Mobile Apps from The Engineering ToolBox

- free apps for offline use on mobile devices

### Air Duct Velocity - SI Units

Air velocity in a duct can be calculated in SI units

v_{ m }= q_{ m }/ A_{ m }

= q_{ m }/ (π (d_{ m }/ 2)^{ 2 })

= 4 q_{ m }/ (π d_{ m }^{ 2 })

= q_{ m }/ (a_{ m }b_{ m }) (2)

where

v_{ m }= air velocity (m/s)

q_{ m }= air flow (m^{ 3 }/s)

A_{ m }= area of duct (m^{ 2 })

d_{ m }= diameter of duct (m)

a_{ m }= width of duct (m)

b_{ m }= width of duct (m)

#### Example - Air Flow Velocity in a Duct

The velocity in a rectangular * 0.5 m x 0.5 m * duct with air flow * 1 m ^{ 3 } /s * can be calculated as

* v _{ m } = (1 m ^{ 3 } /s) / ((0.5 m) (0.5 m)) *

* = 4 (m/s) *

#### Air Flow Velocity Calculator - SI Units

Air velocity can be calculated with the calculator below. Add air volume - * q * - and diameter - * d * - (or length * a * and * b * ).

or alternatively

### Air Ducts - Velocity Diagram

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

The default values are for air flow * 400 cfm (680 m ^{ 3 } /h) * , duct size

*8 in (200 mm)*and velocity

*1150 fpm (5.8 m/s)*.

Download and print Air Ducts - Velocity Diagram!

- make 3D HVAC models with the Engineering ToolBox Sketchup Extension

## 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 - 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.

### Air Ducts - Sizing

Required duct area vs. air flow.

### Air Ducts - Velocity Diagram

Air flow volume, duct size, velocity and dynamic pressure.

### Circular Ducts - Dimensions

Standard size of circular ventilation air ducts.

### Colebrook Equation

Friction loss coefficients in pipes, tubes and ducts.

### Duct Sizing - the Equal Friction Method

The equal friction method for sizing air ducts is easy and straightforward to use.

### Ducts - Cross-Sectional Area vs. Diameter

Circular ducts sross-sectional areas.

### Ducts - Sheet Metal Gauges

Thickness of sheet metal used in ductwork.

### Ducts or Pipes through Steel Joists - Maximum Sizes

Maximum sizes of ducts or pipes through K series joists.

### Ducts Sizing - the Velocity Reduction Method

The velocity reduction method can be used when sizing air ducts.

### Ductwork - Seal Classes

Ductwork air leakage classes.

### Exhaust Outlets - Capturing Air Velocities

Capturing air velocity in front of an exhaust outlet - online exhaust outlet velocity calculator.

### Fluid Flow - Hydraulic Diameter

Calculate hydraulic diameter for pipes and ducts.

### HVAC Ducts - Air Velocities

Recommended air velocities in HVAC 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

### Velocity Units Converter

Convert between speed and velocity units like *m/s, km/h, knots, mph and ft/s*.