What should be the size of the outlet pipe in a joint vent manifold?

The outlet pipe in a joint vent manifold should be one size larger than the largest vent pipe. This requirement is based on hydraulic principles that ensure adequate airflow and prevent pressure buildup in the venting system.

When the outlet pipe is sized larger than the largest vent, it allows for better drainage of gases and liquids, minimizing the risk of condensation and blockages. The larger diameter pipe accommodates the flow rate of all connected vent pipes more effectively, enhancing the overall efficiency and safety of the venting system.

Inadequately sizing the outlet pipe can lead to issues such as inadequate venting pressure or flow restrictions, which could potentially jeopardize the integrity of the system and its compliance with safety standards. Therefore, sizing the outlet pipe as described is a crucial practice outlined in the plumbing codes and the standards set by the Maine Journeyman Oil Fuel Board.