This temperature-responsive automatic opener is specially designed to automatically open and close bifold covers on cold frames. Set it to open between 60°F and 77°F to keep the temperature inside the cold frame from overheating. Winter Storage: It is recommended that your Univent - or at least the cylinder - is removed from your greenhouse or cold frame for the winter. Store it in a dry place and do not forget to lubricate the piston rod before remounting in the spring. Also check that the piston rod moves smoothly.