Holmes Window Fan, Twin: * Dual blade operation * Designed to fit into most double hung and slider windows * Slim design allows for use with window screen in place * Independent electronically reversible motors allow either fan blade to be used for air intake, exhaust or air exchange * Two speed settings * Adjustable extender screen and bonus extender panel help to secure the Holmes fan in larger windows * One-year limited warranty * Holmes window fan model #HAWF2043-WMUM