The maximum developed length of individual fixture vents to vent branches and vent headers shall be determined in accordance with Table 919.2 for the minimum pipe diameters at the indicated vent airflow rates.
The individual vent airflow rate shall be determined in accordance with the following:
| Qh,b= Nn,bQv | (Equation 9-1) |
For SI: Qh,b = Nn,b Qv (0.4719 L/s)
where:
| Nn,b | = | Number of fixtures per header (or vent branch) ÷ total number of fixtures connected to vent stack. |
| Qh,b | = | Vent branch or vent header airflow rate (cfm). |
| Qv | = | Total vent stack airflow rate (cfm). |
| Qv (gpm) | = | 27.8 rs 2/3 (1 — rs) D 8/3 |
| Qv (cfm) | = | 0.134 Qv (gpm) |
| where: | ||
| D | = | Drainage stack diameter (inches). |
| Qw | = | Design discharge load (gpm). |
| rs | = | Waste water flow area to total area. |
 | ||
Individual vent airflow rates are obtained by equally distributing Qh,b into one-half the total number of fixtures on the branch or header for more than two fixtures; for an odd number of total fixtures, decrease by one; for one fixture, apply the full value of Qh,b.
Individual vent developed length shall be increased by 20 percent of the distance from the vent stack to the fixture vent connection on the vent branch or header.
TABLE 919.2
MINIMUM DIAMETER AND MAXIMUM LENGTH OF INDIVIDUAL BRANCH FIXTURE VENTS AND
INDIVIDUAL FIXTURE HEADER VENTS FOR SMOOTH PIPES
| DIAMETER OF VENT PIPE (inches) | INDIVIDUAL VENT AIRFLOW RATE (cubic feet per minute) | |||||||||||||||||||
| Maximum developed length of vent (feet) | ||||||||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | |
| 1/2 | 95 | 25 | 13 | 8 | 5 | 4 | 3 | 2 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 3/4 | 100 | 88 | 47 | 30 | 20 | 15 | 10 | 9 | 7 | 6 | 5 | 4 | 3 | 3 | 3 | 2 | 2 | 2 | 2 | 1 |
| 1 | — | — | 100 | 94 | 65 | 48 | 37 | 29 | 24 | 20 | 17 | 14 | 12 | 11 | 9 | 8 | 7 | 7 | 6 | 6 |
| 11/4 | — | — | — | — | — | — | — | 100 | 87 | 73 | 62 | 53 | 46 | 40 | 36 | 32 | 29 | 26 | 23 | 21 |
| 11/2 | — | — | — | — | — | — | — | — | — | — | — | 100 | 96 | 84 | 75 | 65 | 60 | 54 | 49 | 45 |
| 2 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 100 |