What is a valve or plate that regulates the flow of air in ducts or air handling equipment called?

A device that regulates the flow of air in ducts or air handling equipment is referred to as a damper. Dampers are used to control the amount of air that flows through a system, which can affect the temperature, efficiency, and overall performance of heating, ventilation, and air conditioning (HVAC) systems. By adjusting the opening of the damper, you can either allow more air to pass through or restrict airflow, thus managing the distribution of air within a building.

Fans are primarily used to move air, while filters are designed to remove particles and contaminants from the air. Registers, on the other hand, are the outlets that deliver the conditioned air into rooms, typically containing an integrated damper for airflow control. Therefore, the correct identification of a device that specifically regulates the flow of air is a damper.