An attic fan draws air from inside the attic and expels it to the outside. These fans come in a variety of styles, and different models will be mounted in different ways. In warmer climates, the goal is generally to reduce heat. In colder climates, heat may be less of an issue, and the fan will be installed to reduce moisture levels in the attic.
Attic fans are sometimes confused with whole-house fans. These fans have a different purpose. This style of fan cools the house by pulling air from open windows through the house and into the attic. In select climates, these fans can reduce the temperature in the house on a cool summer night as an alternative to air conditioning. This is different than an attic fan, since the air is blowing into the attic. Whole-house fans serve a completely different purpose.

Attic fans work to reduce heat or moisture within the attic. The fans create active ventilation for the attic. Many attics suffer from insufficient ventilation particularly from passive movement from gable to gable or from soffit to ridge vent. If the air isn’t moving quickly enough, then the heat or moisture builds up. The outside air has to move quickly in order to be effective. When using attic fans, the first step is to properly seal any gaps or openings on the attic floor. Then, the next step is to insulate properly to limit temperature transfer between spaces. Finally, ventilate the attic. The attic fans pull the outside cooler and drier air into the attic and push the hotter and more humid air out.

Yes! Attic fans will reduce heat in the attic. Attics can easily reach over 150 degrees in peak summer time without enough ventilation. Obviously, that’s hot! The fans will exchange the air with the cooler air from the outside. Even if it’s 90 degrees outside, that is still significantly lower than the extreme temperature within an attic. The goal is to keep the air moving so that it has less time to be heated by the solar energy coming through the roof deck.

Yes! Attic fans exchange the air in the attic. In most homes, heat and moisture from within the house travel upwards and end up in the attic. Consequently, the moisture sometimes gets trapped. This can become a major problem if the humid air starts hitting cold surfaces creating condensation. That water leads to the potential for mold and wood rot.
The fans keep the air moving in the attic. As you exchange the air, the fans push out the moisture in that air as well as replace the air with fresh air from the outside. Winter air tends to be very cold and dry. An ATMOX attic controller ensures that the air outside is beneficial to the attic before activating fans.

Fans needed is determined by the size of the attic and the power of the fan. ATMOX generally recommends that the attic air cycles approximately six times per hour when the fans are operating. Calculate the cubic feet within your attic to find the size. Fans are rated by CFM which stands for Cubic Feet per Minute. A typical attic may use four ATMOX Attic Exhaust Fans at 225 CFM each to balance and distribute the airflow.
Other fans on the market may have a much higher CFM, so you may need fewer of those. However, it is is important not to overpower the attic ventilation. One, it can be energy inefficient and use a lot of electricity. Two, if you don’t have enough intake points for air to come in, then the fans may start pulling air from within the living space. More is not always better.