Heat pump for frost protection in an unoccupied house?
We have a vacation home that gets only very occasional use in the winter. Currently, the only source of heat there is a Rinnai 560 WTA propane heater, which we set to 42F when we are not in the house. This has worked to keep the water pipes from freezing, but propane bills can run quite high.
We are now thinking of adding a Mitsubishi Ductless System that both heats and cools (MUZ FH12NA + MSZ FH12HA). (There was so far no cooling system in the house.) Bu we are wondering whether the heating function on this system will meet our needs. Apparently, the thermostat that comes with it cannot be set lower than 50F. So we would either have to keep heating the house to a much higher temperature than previously when we are not there — i.e. to 50 rather than 42, thus much beyond what’s required for frost protection. Or else we would be using the heating function only during those times when we are there (typically only every other weekend or so iin the winter). The first option probably means that any savings due to the heat pump’s higher efficiency vs the propane heater would be more than offset. The second option may mean that it’s not worth it for a house used so little.
My question is: Would it be feasible, and would it make sense, to combine the system with a different or an additional thermostat? E.g., could we just add an external thermostat that simply cuts power to the entire system unless indoor temperature is below 42F?
Thank you for any advice.
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