Sizing Circular Ducts

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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 generation of noise.

ductwork velocity method

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

Maximum Air Volume Flow (m³/h)
Diameter (mm)	Area (m²)	Comfort systems			Industrial systems			High 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

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