What is a requirement for the relief vent in a circuit vent when there are multiple water closets?

A relief vent in a circuit vent configuration is essential for balancing the pressure within the plumbing system, particularly when multiple water closets are involved. The requirement that this relief vent may be a wet vent is particularly significant because it allows the drainage system to efficiently handle both the drainage and venting functions.

In scenarios involving multiple fixtures like water closets that can discharge simultaneously, the potential for negative pressure in the vent system increases. A wet vent allows the sewage and wastewater to flow through while still facilitating proper air circulation, which is vital for maintaining the overall functionality of the drainage system. This design reduces the need for additional vent pipes, ultimately optimizing space and cost.

This ability to utilize the wet vent is especially advantageous in tight construction spaces or when adhering to economic considerations, making it a practical choice in plumbing design. The allowance for wet venting provides flexibility in the design while ensuring compliance with the necessary venting requirements outlined in plumbing codes and practices.