WhisperGreen ENERGY STARa® rated exhaust fansincorporate highly energy efficient DC motors. These models come with variable 2-speed and delay timer controls built-in or as a single speed fans. A motion sensor model is also available. WhisperGreen models are ideal exhaust fans to comply with Green building IAQ standards.Features: Superior performance and quiet operation at .25" w.g. Super energy efficient DC motor SmartFlow technology for constant CFM output CustomVent variable speed control with high/low delay timer (Built-in controls models only) SmartActiona® motion sensor (FV-08VKM3 & FV-13VKM3) ENERGY STARa® qualified fan Enclosed DC motor for long life - rated for 60,000 hours continuous run Easy installation (double hanger bar system) Rustproof paint treatment on galvanized housing Built-in damper to prevent backdraft Fits in 2 x 8 construction UL listed for tub/shower enclosure when used with a GFCI branch circuit wire Thermal fuse protection ASHRAE 62.2, LEED for Homes, ENERGY STAR IAP, CA Title 24, EarthCraft and WA Ventilation Code compliant 6 year warranty on DC motor and 3 year warranty on parts Optional designer grille and radiation damper available