For a 2-inch vent serving multiple fixtures, what is the maximum number of total fixture units allowed?

• A. 6 d.f.u.
• B. 10 d.f.u.
• C. 12 d.f.u.
• D. 18 d.f.u.

Answer: (C)

The maximum number of total fixture units allowed for a 2-inch vent serving multiple fixtures is 12 drainage fixture units (d.f.u.). This is based on plumbing codes and regulations that establish the capacity of vent systems to effectively handle the discharge from multiple fixtures while ensuring proper air circulation and preventing negative pressure that could lead to drainage issues.

In the context of venting, fixture units are a standardized measure that represent the probable demand on a plumbing system from various fixtures. A 2-inch vent is designed to accommodate a specific number of fixture units without risking blockages, siphoning, or inadequate venting performance.

Choosing a figure above 12 d.f.u. for a 2-inch vent would compromise its ability to adequately vent the system, which can lead to problems such as drainage backups or unwanted trap siphoning. Hence, the established maximum of 12 d.f.u. aligns with safe plumbing practices and ensures effective venting for multiple fixtures.