Lowest profile ENERGY STAR available 3 3/8" low profile, fits 2x4 joist size or larger, Customizable fan speed with a Pick-A-Flow airflow selector (1 fan, 2 speeds), Whisper Quiet operation - <0.5 sones at 80 CFM and 1.1 sones at 100 CFM (using 4"duct), Unique L Shaped Bracket for easy DIY installation, UL approved for wall & ceiling installation as well as in shower applications using a dedicated GFCI circuit, For small to medium size rooms, Built-in damper to reduce back drafting