How many fixture units (FU's) can discharge into a wet vent from any one story above the first story?

When determining how many fixture units can discharge into a wet vent from any one story above the first story, it is essential to understand the function of wet vents and plumbing code requirements. A wet vent allows the drainage from one or more fixtures to serve simultaneously as a vent for another fixture or fixtures.

According to plumbing codes, specifically referencing the Uniform Plumbing Code (UPC) and International Plumbing Code (IPC), there are provisions that limit the number of fixture units discharging into a wet vent to prevent issues like excessive pressure changes and to ensure proper drainage.

In this context, the maximum number of fixture units that can discharge into a wet vent from any one story above the first story has been established as four. This guideline is based on ensuring that there is adequate ventilation for the drainage system while allowing sufficient capacity for drainage without creating back pressure.

Thus, the reasoning behind allowing four fixture units is to balance proper air flow through the vents with the handling capacity of the drainage, facilitating efficient waste flow and reducing the risk of clogs or drainage backups. This understanding is crucial for anyone working in plumbing design and installation, as it directly impacts how systems are designed for optimal performance.