A plumber is tasked with sizing the water supply piping for a new commercial kitchen. The kitchen includes multiple sinks, dishwashers, and food preparation areas. What primary factor will determine the overall pipe diameter of the main supply line to the kitchen?

Question: A plumber is tasked with sizing the water supply piping for a new commercial kitchen. The kitchen includes multiple sinks, dishwashers, and food preparation areas. What primary factor will determine the overall pipe diameter of the main supply line to the kitchen?

Answer options:

• The total developed length of the piping system.
• The desired water velocity in the pipes. ✅ The total fixture units (DFU) for all connected fixtures.
• The maximum ambient temperature of the kitchen space.

Correct answer: The total fixture units (DFU) for all connected fixtures.

Explanation: For complex water distribution systems with multiple fixtures, the primary factor for sizing the main supply line is the total demand, which is quantified by summing the drainage fixture units (DFU) or supply fixture units (SFU) for all connected fixtures. This empirical method accounts for the probability of simultaneous use and ensures adequate flow. Developed length and desired velocity are considered in friction loss calculations, but not the primary determinant for overall demand, and ambient temperature is irrelevant for pipe sizing.