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# 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 (df / 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 (ft3 /min)

A i = area of duct (ft2)

df = 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

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### Air Duct Velocity - SI Units

Air velocity in a duct can be calculated in SI units

vm = qm / Am

= qm / (π (dm / 2)2)

= 4 qm / (π dm2)

= qm / (am bm )                                  (2)

where

vm = air velocity (m/s)

qm = air flow (m3 /s)

Am = area of duct (m2)

dm = diameter of duct (m)

am = width of duct (m)

bm = 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 m3 /s can be calculated as

vm = (1 m3 /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 m3 /h) , duct size 8 in (200 mm) and velocity 1150 fpm (5.8 m/s) .

Air Ducts Friction Loss

## Related Topics

### • Ventilation Systems

Design of 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.

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