I used to take care of a neighbors house for a month.  They had it set pretty cold, I never looked at the thermostat so I can't say for sure, but I know it was in the 50's.  They drained the pipes and filled toilets with anti freeze.
Never had a problem so it probably didn't matter.  They also had a generator setup in case the power went off.

On a side note, I have a shop that's about 8600 cubic feet.  The walls aren't insulated but the ceiling is.  Even when the temperature was so cold a couple of weeks ago the temperature never got below 25°.  I suspect if you had a refrigerator running and a decently insulated house it wouldn't freeze in weather that stayed above freezing in the daytime.