The two primary designs in electric attic fans are roof ventilators and gable fans. Roof ventilators are installed directly into the roof of a home, while gable fans are designed to fit into the A-framed shape of existing attic spaces. These units are designed to operate using the electricity of a home and significantly cool attic temperatures, taking some of the burden off of overworked internal cooling systems during warm months.
All electric attic fans operate on the same basic principle of exhausting hot or moist trapped air from the attic to the outdoors. The purpose of this is to maintain a temperature in the attic of a home that is within a few degrees of the temperature outside. Most attics, during the warmest months of the year, can easily exceed 130 degrees Fahrenheit (54.4 degrees Celsius), on hot days. This heat is then transferred to the living areas of the home through interconnected building materials, causing the air conditioning unit to work harder to maintain a comfortable temperature inside.
Roof ventilator electric attic fans are installed directly into the roofing material of the house with access to the attic space. These typically appear from the outside, as short, cylindrical hats that sit just above the roof line. Inside the exterior metal assembly is an electrically powered fan, mesh protective screening, and exhaust vents. The fan works to pump hot air out of the attic using the venting system, while preventing small rodents and insects from entering the home.
Most single family homes require between two and three roof ventilators to adequately move air through the attic. Each unit can be equipped with an internal thermostat that monitors the temperature of the attic. When a pre-set temperature is achieved, the units automatically turn off and do not resume operation until that temperature has been exceeded. This feature prevents the units from continuing to work during winter months, and during evenings which might be cooler than the warmest part of the day.
Gable electric attic fans do not require any roof maintenance to be performed for installation. These units sit directly in the triangular space naturally created by A-frame houses. The fan itself is typically housed in a large, circular assembly which can then be mounted to the frame work of the home. Screening can be added to prevent small animals from entering the space. This type of design often moves more air, sometimes in excess of 1300 cubic feet of air per minute (CFM), than its roof ventilator counterparts, which typically only circulate between 800 and 1000 CFMs.