Model SP Ceiling Exhaust fans are designed for clean air applications where low sound levels are desired. Low sound levels are achieved through quiet running forward curved wheels. Lower CFM levels are attainable with the use of an optional solid state speed controller (Model SSC). Fans are also available with an optional ceiling radiation damper (Model CRD). Key features: Acoustic insulation absorbs sound ensuring quiet operation, Spring loaded aluminum backdraft damper eliminates rattling, External electrical access reduces installation time, Speed controllable, Designer grille included Certifications: AMCA Air & Sound, UL/cUL 507