Superior Moisture and odor control for good indoor air quality, Customizable fan speed with a Pick-A-Flow airflow selector (1 fan, 2 speeds), Whisper Quiet operation - <0.3 sones at 80 CFM and 0.8 sones at 110 CFM (using 4 inchduct), Flex-Z Fast installation bracket for easy installation from below the ceiling. cUL approved for shower installation using a dedictaed GFCI circuit, For medium to large sized rooms, Built-in damper to reduce back drafting