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 in. 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 in. 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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