The Megavent Storm Automatic window opener is a mechanical device that opens and closes Roof Windows automatically without needing electricity. It has a cylinder with an industrial wax like substance which expands with heat and contracts with cold opening and closing the window automatically. An adjustment knob allows one to choose the temperature that it opens at (between about 18 and 25 degrees). The Megavent also has a second cylinder which restricts the speed at which the vent can open, helping to protect it in windy weather. A really high quality good opener. This option changes the opening mechanism for the roof vent from a spindle to a Megavent when purchasing a Greenhouse.