A wall exhaust vent is the portion of an interior ventilation system that blows air outside from a fan mounted into the wall. The entire system consists of a fan cover, ventilation fan and ductwork that leads air outside to the exhaust vent, often covered by a wall cap.
Wall exhaust vents are usually installed in interior spaces that generate moisture and odors, such as kitchens and bathrooms. When combined with an efficient fan system, they prevent the accumulation of noisome smells or excessive humidity that can lead to mold growth.
Fan systems are rated to move air effectively for a given volume, generally measured as cubic feet per minute. The given volume of a bathroom, for example, is the length multiplied by the width and the height. This volume is divided by 7.5 to determine the needed fan airflow rating.
Range hoods, deployed over a cooking range or stove, typically have a built-in fan that connects to an exhaust vent blowing outside. This transfers cooking odors and humidity to the building exterior, preventing mildew formation.
Wall exhaust vents are generally retailed at home improvement store retailers like Lowe's and online at websites like Famcomfg.com and Hvacquick.com. They are built by numerous manufacturers and retail for anywhere from $10 to $60 or more as of 2015.