31
2005 Boreal Geothermal Inc.
www.boreal-geothermal.com
Duct Sizing Guide
Required
CFM
Diameter
in inches
Return Air
Diameter
Required
CFM
37
5
2.25 x 10
3 x 8
3.5 x 6
4 x 5.5
5 x 5
`
5
37
63
5
2.25 x 10
3 x 8
3.5 x 6
4 x 5.5
5 x 5
6
63
100
6
3.25 x 10
4 x 8
5 x 6
5.5 x 5.5
6 x 6
7
100
152
7
3.25 x 14
4 x 11
5 x 8.5
6 x 7
6.5 x 6.5
8
152
212
8
4 x 15
5 x 12
6 x 10
7 x 8
8 x 8
9
212
226
8
4 x 15
5 x 12
6 x 10
7 x 8
8 x 8
10
226
277
9
5 x 15
6 x 12
7 x 10
8 x 9
8.5 x 8.5
10
277
304
9
5 x 15
6 x 12
7 x 10
8 x 9
8.5 x 8.5
12
304
393
10
6 x 15
7 x 13
8 x 11
9 x 10
9.5 x 9.5
12
393
411
12
7 x 18
8 x 16
9 x 14
10 x 12
11 x 11
12
411
655
12
7 x 18
8 x 16
9 x 14
10 x 12
11 x 11
14
655
680
14
8 x 22
9 x 19
10 x 17
11 x 15
12 x 14
13 x 13
14
680
995
14
8 x 22
9 x 19
10 x 17
11 x 15
12 x 14
13 x 13
16
995
1325
16
8 x 30
10 x 22
12 x 18
14 x 16
15 x 15
18
1325
1450
16
8 x 30
10 x 22
12 x 18
14 x 16
15 x 15
20
1450
1750
18
8 x 40
10 x 30
12 x 24
14 x 20
16 x 17
16.5 x 16.5
20
1750
2000
18
8 x 40
10 x 30
12 x 24
14 x 20
16 x 17
16.5 x 16.5
22
2000
2250
20
10 x 38
12 x 30
14 x 26
16 x 22
18 x 19
18.5 x 18.5
22
2250
2600
20
10 x 38
12 x 30
14 x 26
16 x 22
18 x 19
18.5 x 18.5
24
2600
2900
22
12 x 36
14 x 30
16 x 26
18 x 23
20 x 20
24
2900
3400
22
12 x 36
14 x 30
16 x 26
18 x 23
20 x 20
26
3400
3600
24
14 x 38
16 x 32
18 x 28
20 x 25
22 x 22
26
3600
4300
24
14 x 38
16 x 32
18 x 28
20 x 25
22 x 22
28
4300
5250
26
16 x 38
18 x 32
20 x 30
22 x 24
24 x 24
30
5250
6125
28
18 x 38
20 x 34
22 x 30
24 x 28
26 x 26
32
6125
6500
28
18 x 38
20 x 34
22 x 30
24 x 28
26 x 26
34
6500
7250
30
20 x 40
22 x 38
24 x 32
26 x 30
28 x 28
34
7250
7800
30
20 x 40
22 x 38
24 x 32
26 x 30
28 x 28
36
7800
8500
32
22 x 40
24 x 38
26 x 34
28 x 32
30 x 30
36
8500
9200
32
22 x 40
24 x 38
26 x 34
28 x 32
30 x 30
38
9200
9800
34
24 x 42
25 x 40
26 x 38
28 x 34
30 x 32
31 x 31
38
9800
10900
34
24 x 42
25 x 40
26 x 38
28 x 34
30 x 32
31 x 31
40
10900
28 x 40
30 x 36
32 x 34
33 x 33
30 x 42
32 x 38
34 x 36
35 x 35
30 x 45
34 x 40
36 x 38
37 x 37
Rectangular Equivalents
