It is mercury bulb based sorta like the robertshaw valve here:
It's not exactly like this one but real close, you dial it down to the lowest setting and it oughta be able to keep above freezing ok, but I gotta say the pilot light all by itself on the ODS models can keep a hot house warm in spring once you get it cozy in there.Is the thermostatic control ,by room temperature - themobilian_11.gif/images/themobilian_11.gif" alt="themobilian_11.gif" />

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