Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is installing a 2-inch continuous waste and vent system for a double kitchen sink. The fixture unit load for the sink is 3 DFUs. What is the minimum size of the wet vent required for this setup?
- A3 inches
- B1 1/2 inches
- C2 inches
- D1 1/4 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inches
In a wet vent system, the pipe serves as both a drain and a vent. The wet vent must be at least 2 inches in diameter to serve a kitchen sink (which typically has a 1 1/2-inch or 2-inch trap) and also satisfy the DFU load and length requirements. A 2-inch pipe is the minimum for fixtures like kitchen sinks when part of a wet vent system due to the combined function.
Why the other options are wrong
- A. While acceptable, 3 inches is not the minimum required size for this application.
- B. While a 1 1/2-inch pipe can be a fixture drain, it's generally too small to act as a wet vent for a kitchen sink.
- D. This size is too small for a wet vent serving a kitchen sink.
Wet Vent Sizing
A wet vent is a pipe that functions as both a drainage pipe and a vent pipe. It must be sized to adequately handle both the drainage flow and the air circulation requirements, typically requiring a larger diameter than a dedicated dry vent.
- Acts as both drain and vent.
- Must be adequately sized for both functions.
- Minimum 2 inches for kitchen sinks/bathtubs.
- Limits on fixture types and DFU loads served.
Memory trick: Wet Vents are Dual-Purpose Pipes, Needing Extra Size to Avoid Drain Gripes.