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Recommended Air Velocities in Ducts

Ducts and recommended air velocities

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Air flow velocity in ducts should be kept within certain limits to avoid noise and unacceptable friction loss and energy consumption.

Low and Medium Pressure Ducts

  • Maximum friction rate 0.1 - 0.2 inches W.G./100 ft
  • Velocity 1,500 - 2,000 ft/min (8 - 10 m/s)
Air Flow Rate Maximum Velocity
(m3/h) (CFM) (m/s) (ft/min)
< 300 < 175 2.5 490
< 1,000 < 590 3 590
< 2,000 < 1,200 4 785
< 4,000 < 2,350 5 980
< 10,000 < 5,900 6 1,180
> 10,000 > 5,900 7 1,380

High Pressure Ducts

  • Maximum friction rate less than 0.4 inches W.G./100 ft
  • Velocity 2,000 - 3,500 ft/min (10 - 18 m/s)

Shafts

Air Flow Rate Maximum Velocity
(m3/h) (CFM) (m/s) (ft/min)
< 5,000 < 2,950 12 2,350
< 10,000 < 5,900 15 2,950
< 17,000 < 10,000 17 3,350
< 25,000 < 14,700 20 3,940
< 40,000 < 23,500 22 4,300
< 70,000 < 41,000 25 4,900
< 100,000 < 59,000 30 5,800

It is common to keep main duct velocity above 20 m/s (3940 ft/min).

Corridors

Air Flow Rate Maximum Velocity
(m3/h) (CFM) (m/s) (ft/min)
< 5,000 < 2,950 10 2,000
< 10,000 < 5,900 12 2,350
< 17,000 < 10,000 15 2,950
< 25,000 < 14,700 17 3,350
< 40,000 < 23,500 20 3,940

User Areas

  • Offices, receptions, lounges and similar
Air Flow Rate Maximum Velocity
(m3/h) (CFM) (m/s) (ft/min)
< 5,000 < 2,950 10 2,000
< 10,000 < 5,900 12 2,350
< 17,000 < 10,000 14 2,750
< 25,000 < 14,700 16 3,150

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

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