The 4 inch Aura Solar Attic Fan is 4 inches in diameter and has a 12 inch tall collar. The model number is ASF-4-C12-CMF and exhausts air out at 91 CFM. All 4 inch solar gravity fans come with a standard curb mounted flange. These are to be installed on roof curbs.
The Aura Solar Fan uses both solar and wind to power the ventilator. It exhausts air continuously even when there is no sun and the motor is off. It works passively because of the Venturi Effect. When the wind blows against the outer louvers this creates an upward draft which allows air to freely flow in and out of the roof vent.
The 1/8 inch louvers prevent rain, snow, insects, and animals from entering inside the fan.
When the motor is off the attic fan will still ventilate passively. In other words, even the smallest breeze can create exhaust ventilation to draw air out of the fan.