The built-in shutters (also called louvers) on these exhaust fans close when the fans turn off to block out drafts, which helps maintain the efficiency of the building's HVAC equipment. The shutters open when the fans turn on to pull stale air, heat, odors, and some moisture out of barns, garages, and other enclosed indoor work areas to reduce airborne contaminants, improve indoor air quality, and allow occupants to breathe comfortably. These fans also may help regulate the indoor air temperature since they circulate the air. Shutter-mount fans mount to an exterior wall and are suitable for buildings where fans cannot be mounted to the ceiling.