The matter of grates and firepots is most important. The most approved form of grate is the revolving triangular pattern, consisting of teethed triangular bars, connected by gears and turned by means of a detached lever. Fire pots are usually made of cast iron or of steel plate lined with fire-brick, the pot ranging in depth from 12 to 18 inches. In a wrought-iron or steel furnace this fire-brick lining is neces sary because the intense heat may harm the out side shell, but it has not the advantage of giv ing off heat when the coal is first put on, as does the furnace having the cast-iron firepot.
The combustion chamber, or space above the firepot, should be of sufficient size to allow the gases to become thoroughly mixed with the air passing up through the fire or through the openings of the feed door. The radiator, generally constructed of cast iron or steel plate, is used as sort of a reservoir for the gases and air passing over the furnace, till the air has extracted a considerable portion of the heat from the gas. The cold-air box should be large enough to supply a volume of air suffi cient to fill all the hot-air pipes at the same time, the general size or area of the cold-air box being three-fourths the combined area of the hot-air pipes.
Steam and Hot Heating by means of hot water has been in use since time imme morial, and was known prior to the Christian Era, for Seneca mentions the methods by which water was heated in the Therms: at Rome, that of passing water through a coil of brass pipes which passed through a fire. This method was used in France in 1777 by M. Bonnemain, and in London, in 1817, by Marquis de Chatan nes, for heating a conservatory, and in 1822 an Englishman named Bacon introduced the method of using an inclined pipe of large di mensions, but this was not successful because of imperfect circulation. The first hot-water apparatus introduced in this country was the Perkins system, introduced from England by Joseph Nason in 1842. Hot-water heating in the United States has been an evolution since 1880, the most popular heaters at the beginning of this period being the Gurney and the H. B. Smith. In 1885 the Bolton heater was intro duced by the Detroit Heating and Lighting Company, the Mouat heater was the next in succession, and since that time the improve ments have been so many and the demand so great that the price of the hot-water plant has been reduced till it is within the reach of the average householder. Hot-watFe heating is pre ferred by some to steam because the heat is available as soon as the temperature of the water is higher than that of the room, whereas steam yields no heat until 212' degiees is liaised and steam generates, filling the pipes. But in large installations steam is cheaper and has other advantages.
The practice of heating buildings by steam was begun about 1845, the first building so heated being the Eastern Hotel of Boston, and the first factory building the Burlington, Vt., Woolen Mill. The system by which these buildings were heated was introduced by Joseph Nason, and consisted of small wrought iron pipes. From this small beginning have developed the many intricate systems of appa ratus now used for warming buildings.
There are two systems of heating by steam, the direct and the indirect, the former being used in all classes of buildings, both by itself and in combination with other systems. The direct system consists of a furnace and boiler for the combustion of fuel and the generation of steam; a system of pipes, by means of which the steam is conveyed from the boiler to the radiators and the condensed water re turned to the boiler, and the radiators or coils of pipes placed throughout the rooms of a building for the purpose of diffusing the heat to the air. The types of boilers used are many and various; the cast-iron sectional boiler is more commonly used for dwelling-houses and the tubular or water-tube boiler for larger buildings. In the boiler used for heating pur poses only it is not necessary to carry a press. ure of more than two to 10 pounds, the con densation flowing back to the boiler by gravity. When under a high pressure,. the steam for the heating system is forced through a reducing valve and the condensation returned to the boiler by means of a pump or return trap. The system of diffusing the heat by radiators is not standard, no particular one being of greater benefit than another. There are the common cast-iron sectional radiator; the vertical wrought-iron pipes screwed into a cast-iron base; the cast-iron wall radiator, which does not obstruct the flow, and the coils of iron pipes placed along the ceiling or walls, these latter being of late years ornamented and fre quently gilded.
Indirect steam heating has the advantages both of the furnace and of the direct steam, but the cost of installing the system is greater. The main difference between the two lies in the radiator, in the indirect system a special form of beater being beneath the floor and encased in galvanized iron or brick work. Connected with the space beneath the heater is a cold-air box and warm-air pipes at the top are connected with registers in the floors or walls as previously described for furnaces, so that the air in passing through the spaces between the sections of the heater becomes warmed and rises to the rooms above. As compared with furnace heating this method has one great advantage, being less affected by outside wind pressure, as long runs of horizontal pipe are avoided and the heaters can be placed near registers. See FURNACE;