Two Kinds of Attic Ventilation

What is Mechanical Ventilation?

• Mechanical ventilation uses a fan to force air out of the attic. Thermostats or humidistats control the operation of the fan, turning the device on when the temperature or humidity level exceeds the set standards.

Types of Mechanical Vents

• Mechanical vents can be mounted in the roof or gable ends of the home, depending on design. Electricity powers most fans although solar-powered fans are available. One of the drawbacks to mechanical vents is the potential for failures. A fan failure could go unnoticed while heat and humidity build in the attic.

What is Passive Ventilation?

• Passive ventilation uses the natural movement of air for ventilation. This can use the natural winds that move past the roof of the home or can use the fact that hot air rises. Passive vent systems should include about 1 square foot of vent opening for every 300 square feet of the home. More ventilation is needed if the home has large amounts of exposure to sunlight or a dark roof.

Passive Ventilation Types

• Hot air naturally rises. Vents in the soffits allow air to enter while vents at the peak of the roof allow the air to exit the attic. This process works without external power and cannot fail for mechanical reasons. Vent openings in the gable ends of the walls allow the wind to circulate through the attic. All passive vent types use louvers to prevent inadvertent entrance of moisture into the attic space.