Down here in Australia central heating is (also) not very common, and at least around Melbourne it can dip to freezing or below throughout July and August. Generally only one room of the house is heated (often the room with the air conditioner on heat setting). Beds have electric blankets or hot water bottles, and otherwise you wear several layers if you want to be warm elsewhere. The curious thing is that gas is prevalent but gas furnaces are not, and electricity is too expensive to use to heat an entire house.