Variable 10-speed ECM motor. Automatically adjusts fan speed with built-in thermostat, no settings required. Built-in humidistat to help keep humidity % in the attic under 60%. This fan can consistently keep the attic cooler than a traditional attic fan. Up to 2116 CFM on high at 170 Watts, down to 743 CFM at 15 Watts. Plug-and-play (no wiring).