Dr-Fix-It! Equivalent HVAC Duct Sizes By CFM. A table showing typical minimum rectangular and round HVAC duct dimensions required to deliver specific airflows.
Dr-Fix-It! Equivalent HVAC Duct Sizes By CFM
A table showing typical minimum rectangular and round HVAC duct dimensions required to deliver specific airflows.
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Equivalent HVAC Duct Sizes By CFM

A table showing typical MINIMUM rectangular and round HVAC duct dimensions required to deliver specific airflows. Cross sectional rectangular dimensions and diameters are given as Inside Dimension (ID).For example, an 8 X 10 (ID) duct made from 2 inch duct-board would have an outside dimension (OD) of 12 x 14
Table assumes a friction loss of 0.75 inches of water column per 100 feet of duct. Table shows minimum straight duct inside dimension necessary to carry specified air flow CFM. Corners, tees, dampers, vanes, irregular duct liners and other restrictions to airflow are not considered on this table
CFM
Cubic Feet per Minute
Equivant
Rectangular Duct Sizes

Side Dimensions in Inches
Equivant
Round Duct Sizes

Diameter in Inches

100 3 X 4 4
200 3 X 7
4 X 5
5
300 4 X 7
5 X 6
6
400 4 X 9
5 X 7
6 X 6
7
500 6 X 7 8
750 5 X 12
6 X 10
7 X 8
9
1000 7 X 10
8 X 9
10
1250 8 X 10
9 X 9
10
1500 8 X 12
10 X 10
12
1750 8 X 14
9 X 12
10 X 11
12
2000 8 X 15
10 X 12
12
2500 10 X 14
12 X 12
14
3000 12 X 14 14
3500 12 X 15 15
4000 10 X 22
14 X 15
16
4500 12 X 19
14 X 16
17
5000 10 X 25
12 X 20
15 X 16
17
6000 14 X 20
15 X 18
19
7000 12 X 26
16 X 20
20
8000 12 X 30
14 X 25
21
9000 12 X 34
15 X 25
22
10000 12 X 36
16 X 25
20 X 20
23
12500 12 X 45
16 X 30
20 X 24
24
15000 16 X 36
18 X 30
23 X 25
26
17500 16 X 40
20 X 32
25 X 25
28
20000 16 X 45
20 X 35
25 X 28
30
25000 16 X 55
20 X 43
25 X 38
32
30000 20 X 50
30 X 32
34
35000 20 X 55
30 X 35
36
40000 25 X 48
30 X 40
38
45000 25 X 25
32 X 40
40
50000 32 X 45
35 X 40
42




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