Frequently Asked Question

Net free area is the standard of measurement used by the ventilation industry.  It is the unobstructed area of a ventilator through which air may flow.  For example, a C816 cornice vent (a 16” X 8” vent) has a NFA of 65 square inches. The hole cut for this vent would be 15 inches long by 7 inches wide.  The area of the opening would be 105 (15 X 7) square inches, but the net free area of a Lomanco C816 is 65 square inches. The louvered section and screening hinder the air flow and their net free area is lessened by their measurements.