Exhaust fans force out stale indoor air so it can be replaced by fresh outdoor air. They're commonly used to reduce moisture and remove smoke and odors in restaurants, residences, shop and production floors, and commercial buildings. Exhaust fans mount through a cutout in a roof or wall. Belt-driven exhaust fans handle large volumes of air at low static pressures. They run more quietly and allow greater control over fans speeds than direct-drive exhaust fans. Direct-drive exhaust fans have their motor mounted on the fan shaft, so they are more compact and have fewer moving parts than belt-driven fans.