The answer lay in the development of cooking technology in the late 18th and early 19th centuries.  While earlier kitchens had relied almost exclusively on cooking over an open hearth, later kitchens often included additional cooking and heating appliances.  One of these was a boiler, which was installed in kitchens to provide an independent source of hot water.  Boilers were normally large, metal vessels that were built into a masonry base.  A small opening was usually left in the bottom of the masonry base to allow hot coals to be shoveled into the opening to heat the water.  The hot water from the boiler would then be used for cooking or cleaning.  In ca. 1812 when the kitchen was built, boilers were fairly rare and its inclusion at Montpelier demonstrates the relatively high wealth and status of the Madison family.  A similar boiler can be seen in the detached laundry at George Washington’s Mount Vernon as well as at John H. Cocke's residence at Bremo.