As explained, the principle of circulation is exactly the same in this as in a domestic hot-water supply apparatus. The most popular form is that known as the Desideratum. The makers have also introduced a singularly useful tool for cutting all pipes from 2 to 13 in. diameter.
High-pressure Heating, or which might be correctly termed steam heating, consists of piping wholly, the pipe is smaller and of wrought iron unusually strong, and a coil of it placed within the fire-box fulfils the duty of a boiler (no boiler or large container can be used on account of high pressure); from the furnace coil the pipe is carried wherever required, a small quantity of water is put within the apparatus and the air is driven out, after which the apparatus is sealed or closed air and steam tight. When the heat is applied, the water quickly forms steam, which at once finds its way throughout the apparatus and heats it to a much higher temperature than boiling water; and there is comparatively no danger whatever pressure is exerted, as at the worst the pipe only splits, and no disastrous explosion can occur; but this mode of heating cannot be recommended, as it rarely works for any length of time without requiring attention or repairs.
Bacon’s system of heating by water under pressure (J. L. Bacon & Co., 34 Upper Gloucester Place, London, N.W.) is very good, as the pressure is regulated by a valve, and the temperature and pressure never become excessive. This system is worked by small, strong wrought-iron pipes, and the apparatus is wholly filled with water. The great convenience of the small-pipe system recommends it for all purposes, as it can be carried into almost inaccessible places, and can be utilised for warming air, as it passes through inlet ventilators, and for small drying and airing closets, towel dryers, and for numberless small but exceedingly convenient purposes which large cast-iron pipes would be very unsuited for; and the advocates of this system contend that as much heat is radiated from their small pipes as from the ordinary large ones, as the former are heated to a much higher temperature than the latter: in Bacon’s system the highest limit is about 300° F.
The subject of a supply of hot water for baths and other purposes will be discussed in the chapter dealing with the Bath-room. See also p. [995].
Steam Heat.—Steam heat may well be compared with stove and furnace heat. Stove heat corresponds to direct radiation by steam, and furnace heat to indirect. The supply of fresh air from the outside to and over the hot-air furnace, and through hot-air flue into the rooms through registers, is virtually the same as when it is conveyed by means of steam-heated flues in the walls. Exhaust flues, for getting rid of foul air, are equally essential. The stove, as representing direct radiation in the same manner as the steam coil, or plate, in the room, has the advantage over the latter of some exhaust of foul air, however little, even when the smoke-pipe is not jacketed, for the steam heat has none. In comparison with open-stove heat, steam heat is at still greater disadvantage; for open stoves supply all the qualities of complete radiation—the introduction of fresh air and the escape of foul—to a degree wholly unattainable by steam heat, whether direct or indirect, or by hot-air furnaces, which always require special provision for the escape of foul air.
The advantage of stove and furnace heat over steam may be summed up thus:—It is more economical, more uniform, more easy of management, more suitable for small areas to be warmed, and is free from the noises and dangers of steam. Irregularities of the fire in steam heating are a constant source of inconvenience, and sometimes of danger. The going down of the fire during the night-time, or its neglect for a few hours at any time, is followed by condensation of the steam. On the addition of fuel and increase of heat, steam again flows quickly into the pipes where a partial vacuum has formed, and here, on coming in contact with the condensed water, it drives the water violently, and creates such shocks as sometimes occasion explosions; or, at least, produces very disagreeable noises and general uneasiness, and frequently causes cracks and leaks. Hence direct steam heat, which for warming purposes alone is altogether superior to indirect, has been well-nigh abandoned. Indirect steam heat places the leaks out of sight, but they commonly lead to mischief, and require special and expensive provision for access and repair.
Chemical Heaters.—Many salts in solution are capable of absorbing a considerable amount of heat and slowly giving it off as they resume a crystalline state. That most generally used is soda acetate, but an improvement consists in mixing 1 lb. of soda acetate with 10 lb. of soda hyposulphite, the latter assisting the melting of the mass and retarding crystallisation. The mode of applying this principle is to nearly fill a sheet copper or other metallic vessel, such as a foot-warmer, with the solution, and seal it up. When required for warming purposes, the vessel is placed in boiling or hot water till the contents are quite fluid, after which it may be used as a source of heat for 12-15 hours. Obviously the vessel may be placed in an ornamental structure resembling a stove, or used as a foot-warmer, or a muff-warmer, and in many other ways where fire is inadmissible.
Hints on Fuel, &c.—Suggestions for materials which may be used to eke out a scanty supply of coal cannot fail to be useful. One plan consists in well bedding lumps of chalk under small coal. This gives a long-lasting fire, but is apt to emit an unpleasant odour. Another plan is to make clay fire-balls, using common clay, coal dust and cinders with sand, in about the following proportions:—1 cwt. coal dust, 2 cwt. sand, 1½ cwt. clay, well mixing the ingredients, shaping into fist-like lumps, and drying over night before the fire; to be put on when the surface of the fire is clear.
Some further hints for reviving fires will be found under the Sick-room.