What is the maximum fixture unit capacity for any horizontal fixture branch connected to a 4-inch stack?

For a horizontal fixture branch connected to a 4-inch stack, the maximum fixture unit capacity is established according to the International Residential Code (IRC) guidelines. The code specifies that a 4-inch vertical stack can support a certain number of fixture units based on its pipe diameter and the type of system being used.

In this case, referring to the code tables, a 4-inch stack is generally assigned a capacity of 160 fixture units when dealing with horizontal branches. This figure takes into account the ability of the stack to handle drainage effectively without risking interference or obstruction from the fixtures branching off.

It's important to remember that the system must maintain proper flow and venting to avoid issues like clogs or backflow, which underscores the significance of adhering to the specified limits set forth in the IRC. Therefore, the capacity of 160 fixture units for a 4-inch stack is designed to ensure safe and efficient plumbing operation within these parameters.