James,
[For for wood heat forced-air room heating], I recommend using one of these switches that opens when the temperature drops below 115 degrees, and closes when the temp rises above 130 degrees. Mount it where it will “see” the heat but not be exposed the maximum heater temperatures. On the support legs would probably be sufficient. This might have to run through a small relay that has contacts that can handle the motor starting and run currents. Depends on the fan motor ratings. Regards, – David H.