The Lasko electronically reversible twin window fan will keep you cool both day and night. Two independently-controlled motor fans operate in three ways - intake to bring in fresh air, exhaust to push out stale air, and exchange to combine both operations. The digital thermostat senses room temperature and turns the fan on or off automatically to maintain the comfort level of your choice. It fits most windows (double-hung, casement or sliding) from 22 inches to 32 inches. The expandable panels of this fully assembled unit provide a custom fit for your window space and the slim profile ensures that the outdoors is still within view.