Well I didn't hear the furnace overnight but the house is not FREEZING this morning. I'm still heating up with the space heater in the bathroom... I'm keeping this very low because I still have to tightly ration my oil. It didn't get cold quickly overnight even though my rooms started at the same temperature, probably because everything below the top floor was also warmer, rather than just the two rooms with the space heaters, so there was more "heat support" through the whole house.