The energy efficient Panasonic WhisperGreen FV-08VKS3 Ceiling Mount Bathroom Fan - ENERGY STAR incorporates an enclosed DC motor designed for extremely quiet operation. It features the SmartFlow Optimum CFM Technology which is like a brain that monitors and keeps the fan at a constant CFM. Its efficient, cool running motor does not create excessive heat while the built-in damper prevents the outside air from coming through the fan.