How many fixture units are required for a 4-inch soil or waste pipe?

The correct answer indicates that a 4-inch soil or waste pipe can accommodate up to 172 fixture units. This value is based on plumbing codes and standards that provide a systematic approach to determining the appropriate size of plumbing pipes based on the potential load they must handle. Fixture units are a measure of the probable demand on the plumbing system, taking into account the types of fixtures and the expected usage patterns.

In plumbing design, the sizing of pipes is critical to ensure that the system can effectively transport wastewater without causing backups or excessive pressure drops. The 172 fixture units for a 4-inch pipe represent a balance between capacity and the practical considerations of flow rates and drainage requirements. This standardization helps plumbers design efficient and reliable plumbing systems, which is essential for both residential and commercial applications.

Understanding this figure is crucial for anyone in the plumbing field, as it guides decisions on pipe sizing, ensuring compliance with local and national codes.