A plumber is sizing the main cold water supply line for a commercial building with 20 water closets (flushometer valves), 15 lavatories, and 5 service sinks. Using the Uniform Plumbing Code's fixture unit method, and assuming a maximum flow velocity of 2.4 m/s (8 ft/s), what is the primary factor that will determine the final pipe size after calculating the total fixture units?

Question: A plumber is sizing the main cold water supply line for a commercial building with 20 water closets (flushometer valves), 15 lavatories, and 5 service sinks. Using the Uniform Plumbing Code's fixture unit method, and assuming a maximum flow velocity of 2.4 m/s (8 ft/s), what is the primary factor that will determine the final pipe size after calculating the total fixture units?

Answer options:

• The building's height and number of stories.
• The available minimum municipal water pressure.
• The material of the piping system (e.g., copper, PEX). ✅ The total equivalent length of the longest run of pipe.

Correct answer: The total equivalent length of the longest run of pipe.

Explanation: After calculating the total fixture units and determining the probable flow rate, the total equivalent length of the longest run of pipe is crucial for calculating friction losses and ensuring adequate residual pressure at the farthest fixture. This, along with available pressure, helps select the appropriate pipe diameter. While material and municipal pressure are factors, equivalent length directly impacts friction loss calculations for proper sizing.