In a common vent with a pipe size of 2 inches, what is the maximum discharge from upper fixture drains?

In plumbing, DFU stands for Drainage Fixture Units, which are a measure used to estimate the load on a drainage system based on the likely discharge of wastewater from various fixtures. The size of the piping system, including venting and drainage, plays a critical role in determining how many drainage fixture units can be accommodated without causing a bottleneck or backup.

In a common vent system where the pipe size is 2 inches, the maximum discharge from upper fixture drains is determined by the capacity guidelines established by plumbing codes. For a 2-inch vent pipe, the commonly accepted maximum is 4 DFUs. This means that one can safely allow for a cumulative discharge from fixtures that resembles 4 DFUs, ensuring the system operates efficiently without risk of overfilling or interference in the drainage system.

This understanding is essential for plumbing design, guiding plumbers in selecting the right size piping to accommodate the expected load of fixtures connected to the vent, thus ensuring a functional and code-compliant system.