Solar operated greenhouse vent opener. Corrosion resistant construction, Balanced lifting action, Illustrated fitting instructions, this greenhouse vent opener has our special Superior Autovent tube with an adjustable beginning opening temperature of 65 – 75°F. Fully open at 20° higher.  Can lift hinged vents up to 30lbs. These single spring units work best on roof vents. Free Shipping.  If you are interested in purchasing more than 4 of these, we suggest you contact us via phone or email to discuss shipping options.