HVAC Duct Sizing Chart - 0.08 in.w.g./100ft

Round Diameter (in)	Round Velocity (FPM)	Round Area (sq ft)	CFM	Rect Area (sq ft)	Rect Velocity (FPM)	Rectangular Size (in)
4	344	0.087	30	0.139	216	5 × 4
5	403	0.136	55	0.194	283	7 × 4
6	484	0.196	95	0.222	428	8 × 4
7	543	0.267	145	0.347	418	10 × 5
8	587	0.349	205	0.458	447	11 × 6
9	634	0.442	280	0.500	560	12 × 6
10	678	0.545	370	0.681	544	14 × 7
11	720	0.660	475	0.833	570	15 × 8
12	764	0.785	600	0.889	675	16 × 8
13	808	0.922	745	1.125	662	18 × 9
14	847	1.069	905	1.319	686	19 × 10
15	884	1.227	1085	1.389	781	20 × 10
16	920	1.396	1285	1.604	801	21 × 11
17	958	1.576	1510	1.917	788	23 × 12
18	996	1.767	1760	2.000	880	24 × 12
19	1031	1.969	2030	2.257	899	25 × 13
20	1066	2.182	2325	2.625	886	27 × 14
21	1100	2.405	2645	2.722	972	28 × 14
22	1133	2.640	2990	3.021	990	29 × 15
23	1165	2.885	3360	3.444	975	31 × 16
24	1197	3.142	3760	3.556	1058	32 × 16

Round Diameter (in)

Round Velocity (FPM)

Round Area (sq ft)

CFM

Rect Area (sq ft)

Rect Velocity (FPM)

Rectangular Size (in)

344

0.087

0.139

216

5 × 4

403

0.136

0.194

283

7 × 4

484

0.196

0.222

428

8 × 4

543

0.267

145

0.347

418

10 × 5

587

0.349

205

0.458

447

11 × 6

634

0.442

280

0.500

560

12 × 6

678

0.545

370

0.681

544

14 × 7

720

0.660

475

0.833

570

15 × 8

764

0.785

600

0.889

675

16 × 8

808

0.922

745

1.125

662

18 × 9

847

1.069

905

1.319

686

19 × 10

884

1.227

1085

1.389

781

20 × 10

920

1.396

1285

1.604

801

21 × 11

958

1.576

1510

1.917

788

23 × 12

996

1.767

1760

2.000

880

24 × 12

1031

1.969

2030

2.257

899

25 × 13

1066

2.182

2325

2.625

886

27 × 14

1100

2.405

2645

2.722

972

28 × 14

1133

2.640

2990

3.021

990

29 × 15

1165

2.885

3360

3.444

975

31 × 16

1197

3.142

3760

3.556

1058

32 × 16

Note: 5 × 4 represents the minimum practical rectangular duct size for most HVAC applications.

Low Friction Rate Applications (0.08 in.w.g./100ft)

This friction rate is recommended for applications requiring quiet operation and minimal pressure loss. Commonly used in schools, hospitals, libraries, and high-end residential systems where noise control is critical.

Design Notes for 0.08 in.w.g./100ft Systems

Quiet Operation: Low friction rates result in lower air velocities and reduced system noise
Energy Efficiency: Reduced pressure losses lower fan energy consumption
Larger Ducts: Lower friction requires larger duct sizes compared to standard 0.1 systems
Premium Applications: Ideal for schools, hospitals, libraries, and luxury residential
Cost Consideration: Larger ducts increase material and installation costs
Space Requirements: Ensure adequate space for larger duct sizes in ceiling/wall cavities

HVAC Professional Tools

HVAC Duct Sizing Chart - 0.08 in.w.g./100ft

Round and Rectangular Duct Equivalents

Low Friction Rate Applications (0.08 in.w.g./100ft)

Design Notes for 0.08 in.w.g./100ft Systems

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