The hearth is where the iron is charged, melted and puddled. The hearth's shape is usually elliptical; in length and wide. If the furnace is designed to puddle white iron then the hearth depth is never more than . If the furnace is designed to boil gray iron then the average hearth depth is . Due to the great heat required to melt the charge the grate had to be cooled, lest it melt with the charge. This was done by running a constant flow of cool air on it, or by throwing water on the bottom of the grate.