When to use tank heaters

[Katherine1962]

I have been waiting for my 3120 to be built since I ordered it in September. Something I am considering is adding a thermal switch to the tank heater power supply to have it com on at a lower temp. I can't see why it should need to come on in the mid 40 degree range. It either works or it don't. I would think around 36 degrees turning on should provide ample time to keep things from freezing

[DebNJim B]

We stay in NW GA in winter and have seen temps in single digits though rare. 20's and 30's are common. I seldom use the tank heaters, only when temps go low and stay there.
The furnace runs quite a bit so basement stays warm. Also remember the water in the tanks is not pure water, especially the black tank. Soaps and sewage tend to lower the freezing point a bit. I have had only one valve freeze and that was the last chance valve that is exposed. I usually leave that open when we're set up and the other valves closed but I messed up that once.
One could turn those heaters on when it's cold and leave them. They are much like an electric blanket and the thermostat won't activate them above 45 anyway.