This auto vent opener has extra springs to exert more closing force. This makes it suitable for both top hinged windows on the wide of a greenhouse as well as roof vents. The extra springs help to hold the vent firmly in place in windy conditions. Designed to open windows automatically it works by wax within its cylinder expanding when it's hot, pushing a piston to open the window. When it's cool, the wax contracts and stainless steel springs close the window.