What is the maximum dfu for a 3-inch diameter horizontal drain branch according to plumbing regulations?

The maximum drainage fixture units (dfu) for a 3-inch diameter horizontal drain branch is indeed 160. This number is derived from plumbing codes and standards that dictate the capacity of different pipe sizes based on their diameter and the expected flow from various fixture types.

A 3-inch diameter drain is capable of handling a significant volume of wastewater, which is why it can accommodate up to 160 dfu. This capacity allows it to effectively service multiple fixtures without risking backups or flow issues, which is critical for ensuring the reliability and efficiency of a plumbing system.

It's important to reference the relevant plumbing codes or standards, such as the International Plumbing Code (IPC) or any local amendments, to understand how the dfu values are determined based on pipe size. This ensures that plumbing systems are designed with adequate drainage capacity accounted for, promoting proper waste removal and sanitary conditions.

The other choices represent values that exceed the established maximum for a 3-inch drain branch according to the regulations, which would lead to insufficient drainage and potential code violations. Thus, understanding the correct dfu calculation is essential for safe and compliant plumbing design.