Combustion of coal is not greatly promoted by the use of water. Water is and in a forge tire to limit the size of the same. By thus limiting the size of the fire the intensity of the draft through the burning parts is increased, and with it the rapidity of combustion which is in turn followed by a higher temperature. The fuel that has been wet, cakes over and cokes from the heat. This process closes the air spaces between tin-pieces of coal and the draft is then forced to pass up through the burning portion.