Winter is upon us,
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>(unfortunately there's no snow so the frost is going deep).
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>We have an outdoor, above ground insulated cistern that
>we heat with a 120Vac sump pump that's works well.
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>The problem is it's manually controlled, which is inconvenient
>when we leave for a week or two...
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>So we need a thermocouple (thermistor) we put into the
>cistern and cycle it to keep the water temperature at 40F.
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>Is there something on the market that can do that, I've looked
>and haven't found anything yet.
>If not, I'll design and market one.
>Ken
There is self-regulating heating cable that you can wrap around pipes and tanks to prevent freezing. Check to make sure it is compatible with your tank material.
Of course there are also mechanical thermostats with a remote bulb that can directly switch lots of current etc. Very common stuff.