The relief vent in a multi-story building shall be what size?

The relief vent in a multi-story building is required to be the same size as the vent stack to maintain proper system function and prevent the risk of inadequate venting. This ensures that the venting system can handle the maximum anticipated flow of gases and air, particularly during peak usage times. By matching the size of the relief vent to that of the vent stack, it allows for adequate air circulation within the plumbing system, allowing wastewater to flow freely without creating negative pressures that could lead to siphoning of traps or sewer gas intrusion.

Choosing the same size as the vent stack also simplifies the design and installation process, as it avoids the complications that could arise from having a mismatch in size, which could lead to venting issues. Ensuring that both the relief vent and the vent stack are of equal size is a best practice that many building codes endorse to provide reliable performance and safety in plumbing systems.