What is the requirement for the venting area when multiple appliances are connected to a Common Vent?

The requirement for the venting area when multiple appliances are connected to a common vent is that it must be equal to the area of the largest Draft Control Device Outlet plus an additional 50% of the areas of any other outlets. This is crucial because it ensures that the vent has sufficient capacity to handle the combined flue gases from all connected appliances without creating any backdraft or inducing negative pressure, which can lead to unsafe operating conditions.

This calculation allows for the largest outlet to dictate the minimum venting area needed, while the added percentage accounts for variations in the efficiency and combustion characteristics of additional appliances, ensuring proper venting and reducing the risk of exhaust gas accumulation. This approach helps maintain safe operation and compliance with relevant codes and standards.

While other options may consider sizing based on different criteria, they might not adequately ensure the required airflow and safety through the venting system, which is why they are not suitable.