DAMPER SIZES How do I determine the correct size damper? Measure or select the FLEX option the comes with multiple sizes. NOTE EQUIPMENT CAPACITY This information tells us how much air will be moving through the dampers Equipment capacity is listed in "TONS" and can be found by searching for the model number found on the "outside" unit of your AC system. If you cannot determine this information, please provide the Sq Ft. of your home to help approximate the capacity of the equipment.