The coal fired heating system operates on similar principles to those of the domestic central heating system, the major difference being that there are usually at least two or three boilers. These are connected together and provide both heating and hot water.
The coal is stored in a brick or concrete bunker, from where it is fed into the boiler by traveling along a duct in the thread of a long revolving screw, called a worm. On reaching the boiler the coal is mixed in the combustion chamber with coal which is already burning. When heat is not required the fire is kept alight by feeding small amounts of coal into the chamber and then blowing in air to fan the flames. This process is known as kindling.
Water flows into the boiler where it is heated in cast iron sections surrounding the combustion chamber. From here it is pumped away from the boiler, around the heating system, and back into the boiler to be re-heated. Even when the boiler is not running the fire in the chamber can continue to raise the water temperature, therefore a constant circulation is essential to prevent the water from overheating. When the water temperature falls below the setting on the thermostat, typically 80 degrees centigrade, an electric motor drives the worm to feed coal into the chamber. In addition, a second motor drives a fan to force the air into the chamber. After the worm stops, the air motor runs on to keep unburned coal to a minimum.
The smoke from the fire is taken through a flue to a tall chimney where it is dispersed into the atmosphere. The major disadvantages of the coal fired system compared with most others is that it requires regular stoking, or raking of the coal and removing the ashes, and a considerable amount of dust and smoke are created.
