The word cellar meant pantry, or place for food storage.
An example was a salt cellar where they kept salt. The cellar was not always under the house. More often it was off to one side. Usually on the north side of the house and merely a room dug deep in the ground, with a dirt floor for the storing of food.
Cellar was actually a mispronunciation of a French word cella, meaning store-room. The deepness of the underground store-room kept foods cool in summer yet warm enough in winter to be above freezing. When the enclosed ice-box appeared the cellar was useless and also about the same time the central furnace apppeared, so cellar has become a logical place for putting the heating system.
Another name applied to the storage area was root cellar. Often in areas of the country exposed to tornados, these underground rooms were havens of safety for the families during storms.