Net Free Area is a measurement of the open area that exists for air to pass through. The key to effective venting is to balance air intake and air exhaust. The chart below specifies the NFA for our PV and AV vents. This is done according to the diameter of the vent. In addition, our Ventilation Calculator is useful in finding the number of exhaust vents for a given area. Keep in mind that you will need an equal amount of intake and exhaust vents. As a result, achieving proper ventilation. This is in order to balance any space. If you have further questions, do not hesitate to call our office at 1-800-Roofvent or email us at [email protected]