A I R FL OW DY N AM I C S & D UC T S I ZI N G
R E FE R ENC E G UI D E
SUPP LY O R RE TURN DUCT SIZ E / CAPAC I TY
PRO CE S S
(.09 to .10 pressure drop per 100’ EL)
CFM
Round
Rectangular (TD)
Residential Design Process
(No. SL)
50
5”
8 x 6
Load Calcuation
(Heating & Cooling)
ACCA Manual J
75
5”
8 x 6
100
6”
8 x 6
3½ x 10
(110)
Air Distribution
ACCA Manual T
125
6”
8 x 6
3½ x 12
(140)
Air Flow, Equipment
ACCA Manual S
150
7”
8 x 6
3½ x 14
(160)
Selection, Components and
175
7”
8 x 6
Assemblies
200
7”
8 x 6
250
8”
6 x 10
8 x 8
6 x 12
Duct Size Calculation
ACCA Manual D
300
9”
6 x 10
8 x 8
6 x 12
Adjust, Test, Balance
ACCA Residential Duct
350
9”
6 x 10
8 x 8
6 x 12
Diagnostic & Repair
400
9”
8 x 10
8 x 8
6 x 12
500
10”
10 x 10
12 x 8
8 x 12
E QU I VA L E NT L EN G T HS
600
12”
10 x 10
12 x 8
8 x 12
P L E N U M / D U C T F I T T I N GS
700
12”
12 x 10
14 x 8
10 x 12
No. 23
Offset starting collar
10’ EL
800
12”
12 x 10
16 x 8
10 x 12
No. 20
Straight starting collar
35’ EL
900
14”
14 x 10
18 x 8
12 x 12
No. 120SC Snap collar, round
35’ EL
1,000
14”
14 x 10
18 x 8
12 x 12
RO U N D EL B OW S & A N G LE S
1,200
14”
16 x 10
24 x 8
14 x 12
90º elbows
30’ EL
1,400
16”
18 x 10
24 x 8
16 x 12
45º angles
10 - 20’ EL
1, 600
16”
20 x 10
28 x 8
18 x 12
R E GI S TER B O OT S
1,800
16”
24 x 10
30 x 8
20 x 12
No. 24R
90º register boot
30’ EL
2,000
18”
26 x 10
32 x 8
20 x 12
No. 27R
Straight register boot
5’ EL
2,500
18”
30 x 10
20 x 14
24 x 12
No. 28R
End register boot
50’ EL
3,000
20”
36 x 10
24 x 14
28 x 12
RO U N D F I T T I NG S ( TA K EO F F S )
3,500
22”
40 x 10
28 x 14
32 x 12
No. 97
Round starting collar
35’ EL
4, 000
24”
26 x 16
32 x 14
38 x 12
No. 63
Square to round straight
15’ EL
8” Joist - 375 CFM; 10” Joist - 525 CFM (return only)
No. 63A
Square to round elbow
40 - 45’ EL
No. 62
Square to round elbow
40’ EL
CO MMO N D UCT F ITT ING S
No. S5
Round to round (adjustable)
20 - 25’ EL
No. 65
Round to round
20 - 25’ EL
D U C T EL B OW S , R A D I US T HROAT
No. 14
Up to 11”
10’ EL
12” to 21”
15’ EL
No. 63A
No. 16
No. 28R
No. 20
45º Angle
22” to 27”
20’ EL
No. 14
28” to 33”
25’ EL
D U C T EL B OW S , S Q UA RE T HROAT
No. 16
Up to 11”
40’ EL
12” to 15”
55’ EL
No. 27R
90º Elbow
No. S5
No. 23
No. 62
16” to 21”
75’ EL
22” to 27”
100’ EL
28” to 33”
125’ EL
R E T U RN A I R S YST E M
No. 63
No. 24R
No. 97
No. 65
No. 120SC
No. 810
Cold air boot, collar, duct
45- 65’ EL
No. 810