I tend to think that we should keep it in the room we are in or, at night, in the living room. DH insists on keeping it in the coldest room in the house. Last winter, I was woken up one of the really really cold nights by the heating switching on at 2ish in the morning. The controller was on its night time setting so the temp inside the house must have got REALLY low.
we used to keep ours in the hallway next to the vestibule door but realised it was best to be in the living room as its the coldest room in the whole house in winter (needing new carpet underlay as ours is worn).....so best in the coldest room.