Arizona Plumbing Practice Exam 2026 – All-in-One Guide to Master Your Plumbing Certification!

The correct choice is based on the specifics of the plumbing code guidelines regarding venting systems and the sizing of pipes based on fixture units and pipe length. In residential plumbing, the allowable length for a vent pipe before upsizing to a larger diameter is typically dictated by the number of fixture units served.

In this context, with 8 fixture units, plumbing codes provide a maximum allowable length for the waste venting pipe before requiring upsizing. The critical point to consider is that as the length of the vent pipe increases, there is a greater need to accommodate for the airflow and pressure changes within the system. Therefore, for a system with 8 fixture units, this threshold is set at more than 50 feet. Beyond this distance, upsizing the pipe is necessary to ensure proper venting, which helps prevent issues such as siphoning of traps and allows for adequate air flow, thereby maintaining the system's overall function and efficiency.

By following the plumbing code's guidelines and understanding how fixture units and lengths interact, it becomes clear why upsizing is needed specifically at lengths that exceed 50 feet when dealing with 8 fixture units in a waste venting system.