The 4 inch Aura Gravity Ventilator with Curb Mount Flange is 4 inches in diameter and has a 12 inch tall collar. The model AV-4-C12-CMF has 12 inches of Net Free Area (NFA). All 4 inch gravity ventilators come with a standard 7.5 x 7.5 inch curb mount flange.
This roof vent has a curb mount flange which allows for easy installation on AVP's prefabricated roof curbs. In other words, the flange will fit over roof curbs or an existing base with a 7 inch diameter.
The Aura Gravity Ventilator works like a roof turbine but with no moving parts.
Gravity vents rely on the Venturi Effect which occurs when the wind blows against the outer louvers to create an upward draft. As a result, forcing air to flow out of the vent. Thus, removing heat from the attic in the summer and moisture in the winter. This allows for year-round ventilation on low slopes or flat roofs.
Even the smallest breeze can create exhaust ventilation to draw air out of the gravity vent. Therefore, wind speeds of 11 mph for a 4 inch Gravity Ventilator produces 62 CFM of air exhaust for attic ventilation.
The diameter size of all roof vents determines the Net Free Area, also known as the "NFA". NFA is the measured amount of opening each vent offers at each specific size. to be available for venting air through a specific vent size. The calculator below will find the overall number of vents needed to effectively ventilate the targeted attic space.
Once you have the area, the numbers shown below are the number of vents of that size which would ventilate the specified area with both 1/300 and 1/150 rule.
The roof vent calculation values shown above are for the exhaust portion of the roof. The same amount of net free air inches is needed for air intake as well. Proper roof ventilation consists of 50% air exhaust and 50% air intake.