In a central ac system, air is heated or cooled at a central location and then is distributed across various rooms or zones via fans and ducting networks.

In this air is supplied to every room at a constant rate, it is of great importance to calculate what is the required air flow for each room at the initial design stage. The desired airflow in each room can be achieved either by carefully varying the dimensions of each duct branch or by installing manual volume control dampers or constant air volume regulators.