Holmes' window fans are designed specifically to fit virtually all windows. Holmes window fans have special features for this purpose, such as extender panels and windowsill holders. Installation of our window fans is designed to be quick and easy, with no tools required. Options available on window fans include the following: electric reversibility for air intake, air exhaust, or even air exchange; thermostats; digital thermostats; temperature displays; and sleep settings for quieter performance at night. Thermostats are particularly useful on window fans, as most people tend to use this type of fan in their bedroom. You can set the thermostat to your desired comfort level. The thermostat will then automatically turn the window fan on or off, in order to maintain your set temperature. This feature is especially welcome in the fall or early spring. As the night air cools down, your fan will turn off, and then turn on again as the morning sun begins to warm your room.