What is the minimum fixed opening required when an automatic damper is installed on an appliance with a standing pilot?

The correct answer regarding the minimum fixed opening required when an automatic damper is installed on an appliance with a standing pilot is based on safety and operational efficiency. In systems with standing pilots, the need for sufficient combustion air is critical to ensure that the pilot remains lit and provides a reliable ignition source for the appliance.

A minimum fixed opening of 20% is recognized as necessary to allow for adequate airflow. This percentage ensures that there is enough air to support combustion, particularly when the damper is closed or partially closed, which can happen based on system demand or operational mode. A larger opening helps to prevent issues such as pilot outage or incomplete combustion, which can lead to safety hazards and equipment inefficiency.

In this context, the other percentages listed (10%, 30%, or 40%) do not meet the standard requirement for the safe operation of appliances with standing pilots. While higher percentages can promote greater airflow, the 20% minimum is specific and is aligned with codes and safety standards designed to balance sufficient air intake with overall efficiency for the appliance's operation.