A vertical wet vent must have a minimum pipe size of how many inches when serving a total fixture unit load of 9 d.f.u.?

• A. 2 inches
• B. 3 inches
• C. 4 inches
• D. 5 inches

Answer: (B)

In plumbing code requirements, a vertical wet vent serves to allow drainage and venting simultaneously for multiple fixtures. The size of the wet vent is determined based on the total fixture unit load it is serving.

For a total fixture unit load of 9 drainage fixture units (d.f.u.), plumbing codes typically specify that a minimum pipe size of 3 inches is necessary for proper function. This size ensures adequate flow capacity to handle the drainage from the fixtures while also allowing for the necessary air circulation to prevent siphoning of traps, which could lead to issues such as drain line clogging and sewer gas entry.

When dealing with fixture units, it's essential to consult local plumbing codes or standards, such as the International Residential Code (IRC), which outlines the relationships between fixture units and required pipe sizing. For a load of 9 d.f.u., the specification of a 3-inch pipe is sufficient to accommodate drainage requirements, while promoting effective venting. Smaller pipe sizes would not provide adequate drainage capacity, potentially leading to drainage issues and code violations.