What is the minimum size for a waste stack vent discharging 8 DFU into the stack?

The minimum size for a waste stack vent discharging 8 Drainage Fixture Units (DFU) into the stack is 1 1/2 inches. This size is determined by plumbing codes that establish the minimum requirements for venting in order to ensure proper functionality and to prevent issues such as siphoning, backpressure, and inadequate venting, which can lead to drainage problems or sewer gas entering the living space.

When a plumbing system is designed, the fixture unit rating indicates the probable demand on the drainage system. For 8 DFUs, the code specifies a vent size that can adequately handle the flow and pressure variations in a way that ensures the system operates efficiently.

Larger sizes for vent stacks are necessary as the number of DFUs increases, as they must accommodate both the discharge of wastewater and the gases produced in the system. Based on established plumbing standards, a 1 1/2-inch pipe provides the necessary capacity for 8 DFUs. Smaller diameters would likely lead to insufficient venting, creating problems in the drainage system.