Recommended Air Velocities in Ducts

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

Air Flow Rate Maximum Velocity

(m3/h) (CFM) (m/s) (ft/min)

< 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)

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