PRODUCT DESCRIPTION Maintain a comfortable temperature indoors with the Holmes Reversible Twin Window Fan. Designed to fit most double-hung and slider windows, this double window fan takes in fresh, cool air from the outdoors to provide cooling comfort. Each of the unit's two fans can be independently reversed, allowing you to intake fresh air, exhaust stale air, or exchange air for full-room circulation. Featuring two speed settings and a one-touch programmable thermostat, the fan lets you easily adjust airflow in accordance with your personal comfort level. Water-resistant motors make the fan safe for use during rainy weather. And thanks to its adjustable extender screen and extender panel, the fan can fit securely in a wide range of window sizes. Control the thermostat and 2 digital comfort settings with the 1Touch controls. It's in with the good air and out with the bad air with the Holmes® Electronically Reversible Twin Window Fan . This window fan operates quietly and efficiently by taking-in fresh, cooler, outdoor air and exhausting stale, warm, indoor air for cooling comfort. AMAZON.COM This double window fan draws in fresh, cool air from the outside or exhausts stale, hot air from inside. It can also do both simultaneously, because each of the two fans can be set independently to draw in or exhaust out, allowing the unit to exchange inside and outside air. Operable either manually or automatically--with its thermostat turning the fans off and on to maintain a selected temperature--the unit has a one-touch electronic control and two speeds so it can be adjusted to conditions. It's designed to fit double-hung, vertical-slider, and casement windows. A built-in 7-inch extender and extra 3-inch extender permit custom fitting for windows from 24 to 37 inches wide. Because the unit is lightweight plastic it can be moved easily from room to room. The fans have six blades and measure 8-1/2 inches in diameter. Overall, the unit is 12-1/4 inches high, arrives fully assembled, and carries a three-year warranty against defects.