Sumnacon Solar Heat Sensitive Automatic Greenhouse Vent Opener Auto Vent Kit for Greenhouses Window, Max. Lifts 30 Lbs (Double Spring Vent Opener) Ideal for your greenhouse window--opens and closes your greenhouse window as the temperature changes automatically Can be clamped onto or screwed onto your greenhouse frame. Suitable for most greenhouses. Fully open distance: 45cm / 18" Fully open temperature: about 30/ 86(depending on adjustment and load) Use solar energy to open green house window, environmental friendly. Including fittings & installation manual.