Duct fitting pressure drop coefficients for
rectangular and round diverging wyes
From ASHRAE (1989), with permission
![]() |
Branch Cc,b for q = 45°
Vb / Vc | ||||||||||
0.1 |
0.2 |
0.3 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
0.9 |
||
Ab / Ac |
0.8 |
0.78 |
0.62 |
0.49 |
0.40 |
0.34 |
0.31 |
0.32 |
0.35 |
0.40 |
0.7 |
0.77 |
0.59 |
0.47 |
0.38 |
0.34 |
0.32 |
0.35 |
0.41 |
0.50 |
|
0.6 |
0.74 |
0.56 |
0.44 |
0.37 |
0.35 |
0.36 |
0.43 |
0.54 |
0.68 |
|
0.5 |
0.71 |
0.52 |
0.41 |
0.38 |
0.40 |
0.45 |
0.59 |
0.78 |
1.0 | |
0.4 |
0.66 |
0.47 |
0.40 |
0.43 |
0.54 |
0.69 |
0.95 |
1.3 |
1.7 |
|
0.3 |
0.66 |
0.48 |
0.52 |
0.73 |
1.2 |
1.8 |
2.7 |
3.7 |
4.9 |
|
0.2 |
0.56 |
0.56 |
1.0 | 1.8 |
3.2 |
4.9 |
7.1 |
9.6 |
13 |
|
0.1 |
0.60 |
2.1 |
5.1 |
9.3 |
16 |
- |
- |
- |
- |
Branch Cc,b for q = 90°
Vb / Vc | ||||||||||
0.1 |
0.2 |
0.3 |
0.4 |
0.5 |
0.6 |
0.7 |
0.8 |
0.9 |
||
Ab / Ac | 0.8 |
0.95 |
0.92 |
0.92 |
0.93 |
0.94 |
0.95 |
1.1 |
1.2 |
1.4 |
0.7 |
0.95 |
0.94 |
0.95 |
0.98 |
1.0 |
1.1 |
1.2 |
1.4 |
1.6 |
|
0.6 |
0.96 |
0.97 |
1.0 |
1.1 |
1.1 |
1.2 |
1.4 |
1.7 |
2.0 |
|
0.5 |
0.97 |
1.0 |
1.1 |
1.2 |
1.4 |
1.5 |
1.8 |
2.1 |
2.5 |
|
0.4 |
0.99 |
1.1 |
1.3 |
1.5 |
1.7 |
2.0 |
2.4 |
3.0 |
3.6 |
|
0.3 |
1.1 |
1.4 |
1.8 |
2.3 |
3.2 |
4.3 |
5.5 |
6.9 |
8.5 |
|
0.2 |
1.3 |
1.9 |
2.9 |
4.1 |
6.2 |
8.5 |
11 |
- |
- |
|
0.1 |
2.1 |
4.8 |
8.9 |
14 |
- |
- |
- |
- |
- |
Main Cc,s for q = 90°
vs / vc |
0 |
0.1 |
0.2 |
0.3 |
0.4 |
0.5 |
0.6 |
0.8 |
1.0 |
Cc,s | 0.40 |
0.32 |
0.26 |
0.20 |
0.14 |
0.10 |
0.06 |
0.02 |
0 |