The 18 inch Aura Gravity Ventilator with Curb Mount Flange is 18 inches in diameter and has a 4 inch tall collar. The model number is AV-18-C4-CMF and has 200 inches of Net Free Area (NFA). All 18 inch gravity ventilators come with a standard 22″ x 22″ square curb mount flange.
This roof vent is engineered with a curb mount flange which allows for easy access to the attic or duct below. In other words, the flange is designed to fit over roof curbs or an existing base of the same diameter. As a result, this gives the vent head extra clearance allowing for installation in all climate zones.
To determine the number of vents you may need, see our Vent Calculator.
The Aura Gravity Ventilator works like a roof turbine but with no moving parts.
Aura Gravity Ventilators rely on the Venturi Effect when the wind blows against the outer louvers. As a result, this creates an upward draft allowing air to freely flow in and out of the vent. The Aura Gravity Ventilator removes heat in the summer and moisture from the attic in the winter for year-round ventilation on low slope or flat roofs.
Even the smallest breeze can create exhaust ventilation so that air is drawn out of the gravity vent. This movement of air is proportional to the wind speed and is measured in cubic feet per minute (CFM). Therefore, wind speeds of 11 mph for an 18 inch Gravity Ventilator produces 634 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.