Holmes Products HAWF2043

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 two 3-inch extenders 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.