Controlling temperatures in a cold frame or greenhouse is straightforward with this automatic control.  

It incorporates a gas-charged cylinder of adjustable volume. As the temperature rises, the gas expands; 

it will open a 15 lb window, more than adequate in cold frames and greenhouses. 

A simple adjustment lets you control the operating range. As temperatures fluctuate, the 12-1/2" long unit will open and close a window as necessary to prevent disasters. 

Non-rusting anodized aluminum.