Ductwork and recommended air velocities
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 Rate | Maximum 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
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- Maximum friction rate less than 0.4 inches W.G./100 ft
- Velocity 2000 - 3500 ft/min (10 - 18 m/s)
Shafts
| Air Flow Rate | Maximum 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 Rate | Maximum 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
Airflow 2 4 16 Equals
| Air Flow Rate | Maximum 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)
| Applications | Recommended max. Velocity (ft/min) | |||
|---|---|---|---|---|
| Main Ducts | Branch Ducts | |||
| Supply | Return | Supply | Return | |
| Apartments | 1000 | 800 | 600 | 600 |
| Banks | 2000 | 1500 | 1600 | 1200 |
| Hospital rooms | 1500 | 1300 | 1200 | 1000 |
| Apartments, Hotel rooms | 1500 | 1300 | 1200 | 1000 |
| Industrial | 3000 | 1800 | 2200 | 1500 |
| Libraries | 2000 | 1500 | 1600 | 1200 |
| Meeting rooms, cafeterias | 2000 | 1500 | 1600 | 1200 |
| Offices | 2000 | 1500 | 1600 | 1200 |
| Residences | 1000 | 800 | 600 | 600 |
| Restaurants, stores | 2000 | 1500 | 1600 | 1200 |
| Auditoriums, churches, cinemas, theaters | 1300 | 1100 | 1000 | 800 |
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
- Air Ducts - Velocity Diagram - Air flow volume, duct size, velocity and dynamic pressure
- Air Flow and Velocity due to Natural Draft - Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference
- Duct Velocity - Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator
- Ductwork Seal Classes - Ductwork prone to air leakages
- Pressure Classifications of Duct Systems - Duct systems are commonly divided into three pressure classifications
- Speed and Velocity Converter - Convert speed and velocity units - m/s, km/h, knots, mph and ft/s
- Spiral Ducts - Dimensions - Standard dimensions of spiral ducts - Imperial units
- Velocity Classification of Ventilation Ducts - Recommended air velocities in ventilation ducts
Tag Search
- en: ducts air velocity speed ductwork
Flexible Duct Friction Loss Calculator
1. Enter Friction Loss Per 100' of duct (inches of water), Duct Airflow (CFM), Duct Length and the number of bends.
2. Read Duct Diameter (inches) and Duct Velocity (FPM).
1. Enter Round Duct Diameter (inches), Duct Airflow (CFM), Duct Length and the number of bends.
2. Read Friction Loss Per 100' of duct (inches of water) and Duct Velocity (FPM).
Sheet Metal Duct Friction Loss Calculator
1. Enter Duct Airflow (CFM), Duct Velocity (FPM), Duct Length and the number of bends.
2. Read Round Duct Diameter (inches) and Friction Loss Per 100' of duct (inches of water).
Airflow 2 4 16 Inch
1. Enter Friction Loss Per 100' of duct (inches of water), Duct Airflow (CFM), Duct Length and the number of bends.
2. Read Duct Diameter (inches) and Duct Velocity (FPM).
1. Enter Round Duct Diameter (inches), Duct Airflow (CFM), Duct Length and the number of bends.
2. Read Friction Loss Per 100' of duct (inches of water) and Duct Velocity (FPM).
Equivalent Rectangular Duct
2.4 Naruto
1. Enter Round Duct Diameter.
2. Enter the Desired Length of the Rectangular Duct.
Airflow 2 4 16 As A Decimal
Equivalent Round Duct Diameter
1. Enter the Length of the Rectangular Duct.
2. Enter the Width of the Rectangular Duct.