I would imagine some bad smells could survive the lower temperatures.  

Temperature in the unit has gone as low as 40 degrees because of this.

As long as the compressor is not in danger of overheating, the only hangup should be how much temperature drop is across the unit. 

I personally think you'd be able to install a lock over the thermostat as long as the thermostat was left at an inhabitable temperature.

If you have hydronic radiant heat (in-floor/wall/or ceiling), solar thermal is capable of heating the water sufficiently on its own (meaning you can have a smaller in-line boiler or hot water heater as an ancillary heat source for a string of overcast winter days when the array may not be able to sustain the temperature of the storage tank.

There might be 30 degree temperature swings over the course of a day.  

Hi @Sarah Byun,The temp is the temperature at the thermostat not anywhere else so just something to keep in mind.

Are they able to control the temperature of the radiator heat with the thermostat?

Let her know the cell phone and text is only for emergencies related to temperature, water or fire.

Imagine my poor father's surprise while working in his workshop in the room below as the temperatures outside rose into the 90s and our "toilet" baked in the heat.