Final answer:
The allowable number of fixture units connected to a vent stack varies and is determined based on local building codes, which reference standards like the IPC or UPC. The capacity relates to the vent stack's pipe diameter and length, and proper calculations are needed to ensure compliance and adequate venting.
Step-by-step explanation:
The number of fixture units allowed to connect to a vent stack depends on the building codes prevalent in the area where construction is taking place. These codes are often based on standards such as the International Plumbing Code (IPC) or the Uniform Plumbing Code (UPC). Both have tables and formulas to help determine the maximum number of fixture units that may be serviced by a vent stack of a given size.
Specifically, the capacity of the vent stack in terms of fixture units is determined by the diameter of the vent pipe and the developed length of the vent system. It is important to consult the local building codes to ensure compliance, as exceeding the allowed number of fixture units can result in inadequate venting, leading to poor drainage and possibly violating code. A licensed plumber or engineer should be consulted to determine the specific requirements for a given plumbing installation.