The Automatic Vent Opener was designed to automatically control the temperature, humidity and provide additional ventilation when needed, making gardening easier. As the air inside the greenhouse warms, the vent gradually opens to allow the correct amount of air flow into the greenhouse and closes when the optimal temperature is reached. The vent arm was designed with a metal cylinder containing wax which expands when heated to push a piston, which raises the window, as the air gets warmer, then contracts as it cools, closing with the use of a spring and resetting the piston. All you need to do is to install it on your roof vent window and it automatically starts working. The Automatic Vent Opener operates without the use of electricity and works with all our Greenhouse models only. Color: Metallic.