An improved apparatus of the above description has been invented by M. B. Dyott, of Philadelphia, Pa., who has taken measures to secure a patent. The object) aimed at in the improvements, is to obtain as much caloric as possible from the furnace, or, in other words, to heat the greatest quantity of cold air, and to obtain the largest amount ol heat from it. This purpose is effected by placing a cylindrical flue inside the fire cfiamber, so that a large radiating surface is exposed, up which the cold air passes, and by fixing outside the same air chambers or drums, through which the hot air from the fire chamber circulates by means of tubes, and which communicate with one another by a similar method. These air chambers or drums are so arranged as to allow a eurrent of cold air to act upon the outer surface of the fire chamber, both for the purpose of heating the eir and also of preventing the fire chamber from being injured by the action of the fire. The arrangements for the admission of the cold air, and for the circulation of the hot air are very simple and complete.