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HVAC Ducts - Air Velocities

Recommended air velocities in HVAC ducts.

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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.

air velocity calculator

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)

HVAC Ducts - Maximum Air Velocities
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

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

Shafts

HVAC Ducts - Maximum Air Velocities - 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

HVAC Ducts - Maximum Air Velocities - 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

HVAC Ducts - Maximum Air Velocities - User Areas
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)

HVAC Ducts - Maximum Air Velocities - Low Velocity Systems
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)

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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.
Duct Systems - Pressure Classifications
Duct systems are commonly divided into three pressure classifications.
Duct Velocity
Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator.
Ductwork - Seal Classes
Ductwork air leakage classes.
Natural Draft - Air Flow Volume and Velocity
Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference.
Spiral Ducts - Dimensions
Standard dimensions of spiral ducts - Imperial units.
Velocity Classification of Ventilation Ducts
Recommended air velocities in ventilation ducts
Velocity Units Converter
Convert between speed and velocity units like m/s, km/h, knots, mph and ft/s.

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