Pechka is a diminutive of pech, but when used to refer to those Slavic-style rural home stoves it does not in any way imply a smaller size. If anything, the things were massive and served as a food oven, a heater fireplace, and a bed all at the same time. This is one of the cases where a diminutive was widely used just to express some extra affection for this integral part of the household (only second in importance to the walls and the roof).