Sizing Circular Ducts

A rough guide to maximum air volume capacity of circular ducts in comfort, industrial and high speed ventilation systems

Maximum air velocity in the ducts should be kept below certain limits to avoid unacceptable noise generation.

ductwork velocity method

The values from the table below can be used for rough sizing of ducts in comfort, industrial and high speed ventilation systems.

Maximum Air Volume Flow (m3/h)
Diameter
(mm)
Area
(m2)
Comfort systemsIndustrial systemsHigh speed systems
Main ducts Secondary ducts Connecting ducts Main ducts Secondary ducts Connecting ducts Main ducts Secondary ducts Connecting ducts
Speed (m/s)
5.5 4 2 10 6.5 4 14 9 6.5
63 0.003 62 45 22 112 73 45 157 101 73
80 0.005 99 72 36 181 118 72 253 163 118
100 0.008 155 113 57 283 184 113 396 254 184
125 0.012 243 177 88 442 287 177 618 397 287
160 0.020 398 289 145 723 470 289 1013 651 470
200 0.031 622 452 226 1130 735 452 1583 1017 735
250 0.049 971 707 353 1766 1148 707 2473 1590 1148
315 0.078 1542 1122 561 2804 1823 1122 3926 2524 1823
400 0.126 2487 1809 904 4522 2939 1809 6330 4069 2939
500 0.196 3886 2826 1413 7065 4592 2826 9891 6359 4592
630 0.312 6169 4487 2243 11216 7291 4487 15703 10095 7291
800 0.502 9948 7235 3617 18086 11756 7235 25321 16278 11756
1000 0.785 15543 11304 5652 28260 18369 11304 39564 25434 18369
1250 1.227 24286 17663 8831 44156 28702 17663 61819 39741 28702

Related Topics

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

Related Documents

  • Friction Loss in Air Ducts - Friction loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - imperial and SI units
  • Duct Velocity - Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator
  • Air Ducts - Friction Loss Diagram - A major loss diagram for air ducts - Imperial units ranging 10 - 100 000 cfm
  • Air Ducts Sizing - The ductwork of ventilation systems are often sized with either the Velocity, the Constant Pressure Loss (or Equal Friction Loss) - or the Static Pressure Recovery Methods
  • Equal Friction Method - The equal friction method for sizing air ducts is easy and straightforward to use
  • Design of Ventilation Systems - Design procedure for ventilation systems - air flow rates, heat and cooling loads, air shifts according occupants, air supply principles

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