The controller on my boiler will shut it down when it hits 140 to conserve heat. You need something that will open a normally closed contact when it falls below a certain temp....not sure what that would be though....you may be able to find a snap disk that does that.
Yup my Heatmor 400 dual fans when it’s out of wood both fans continue to fill the air box with charge air that goes up the pipe. I put a wifi bbq thermometer to see water temps so I can monitor the burn before it exhausts wood supply The circulator pumps run steady so I’m not worried about a freeze up , but I agree with Sams heat loss observation, less than optimal .
