With Vent-Miser™, stop heating and cooling unoccupied rooms and start saving on energy bills! Battery-operated vent with timer can be set to automatically open and close—forcing air from unoccupied rooms into other parts of the house. Vent-Miser™ works independently of heating/cooling systems; digital module removes for programming. Specify size: 4" x 12", 4" x 10", 2" x 12". Uses 2 AAA batteries (not included).