Air Duct Velocities

Ductwork and recommended air velocity

Flow velocity in air ducts should be kept within certain limits to avoid noise and unacceptable friction loss and energy consumption. Low velocity design is very important for the energy efficiency of the air distribution system. Doubling the duct diameter reduces the friction loss by factor 32.

Low and Medium Pressure Loss Ducts

  • Maximum friction rate 0.1 - 0.2 inches W.G./100 ft
  • Velocity 1500 - 2000 ft/min (8 - 10 m/s)
Air Flow RateMaximum Velocity
(m3/h)(CFM)(m/s)(ft/min)
< 300 < 175 2.5 490
< 1000 < 590 3 590
< 2000 < 1200 4 785
< 4000 < 2350 5 980
< 10000 < 5900 6 1180
> 10000 > 5900 7 1380

High Pressure Loss Ducts

  • Maximum friction rate less than 0.4 inches W.G./100 ft
  • Velocity 2000 - 3500 ft/min (10 - 18 m/s)

Shafts

Air Flow RateMaximum Velocity
(m3/h)(CFM)(m/s)(ft/min)
< 5000 < 2950 12 2350
< 10000 < 5900 15 2950
< 17000 < 10000 17 3350
< 25000 < 14700 20 3940
< 40000 < 23500 22 4300
< 70000 < 41000 25 4900
< 100000 < 59000 30 5800

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

Corridors

Air Flow RateMaximum Velocity
(m3/h)(CFM)(m/s)(ft/min)
< 5000 < 2950 10 2000
< 10000 < 5900 12 2350
< 17000 < 10000 15 2950
< 25000 < 14700 17 3350
< 40000 < 23500 20 3940

User Areas

  • Offices, receptions, lounges and similar
Air Flow RateMaximum Velocity
(m3/h)(CFM)(m/s)(ft/min)
< 5000 < 2950 10 2000
< 10000 < 5900 12 2350
< 17000 < 10000 14 2750
< 25000 < 14700 16 3150

Typical Air Velocity Guidelines

Low Velocity Duct Systems

  • typical 400 - 2000 ft/min (2 - 10 m/s)
ApplicationsRecommended
Maximum
Velocity
(ft/min)
Cafeterias 1800
Stores, restaurant, shops, banks 1500
Offices, libraries, class rooms 1200
Apartments, hotel rooms 1000
Auditoriums, churches, cinemas, theaters 800
Residences 600

Medium Velocity Duct Systems

  • typical 2000 - 2500 ft/min (10 - 12.5 m/s)

High Velocity Duct Systems

  • typical 2500 - 3000 ft/min (12.5 - 15 m/s)

Related Topics

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

Related Documents

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