A 3-inch waste stack vent may be used for a maximum total discharge to the stack of how many d.f.u.?

• A. 20 d.f.u.
• B. 22 d.f.u.
• C. 24 d.f.u.
• D. 26 d.f.u.

Answer: (C)

The maximum total discharge allowed for a 3-inch waste stack vent corresponds to 24 drainage fixture units (d.f.u.). This value is derived from plumbing codes that dictate the capacity of various pipe sizes based on their diameter.

In this case, the 3-inch diameter is designed to handle a specific volume of wastewater while preventing potential issues such as backflow and providing adequate venting for the drainage system. The allowance of 24 d.f.u. for a 3-inch waste stack reflects both the physical limitations of the pipe and the hydraulic principles related to fluid flow within the plumbing system.

Understanding the relationship between pipe size and drainage fixture units is crucial for a plumbing inspector to ensure that systems are designed and installed properly to manage waste efficiently and safely. This also reinforces the importance of following code requirements to prevent drainage problems in residential plumbing.