42. Gurney Stove. 43. Convoluted Stove.
Another good form is “Constantine’s Convoluted Stove” (J. Constantine and Son, 23 Oxford Street, Manchester), Fig. 43. Instead of solid gills, there are a series of perpendicular convolutions which double the heating surface, and the makers’ claim to greater efficiency is no doubt correct. This stove, however, should be classed with hot-air furnaces, as it is not made in small sizes for direct heating; but for warming large buildings, churches, &c., for heating laundry drying-rooms, Turkish baths, &c., it is to be highly recommended.
The German principle, which might advantageously be adopted to a greater extent in England, is to build a fire-brick structure with the furnace at the base and the flue winding from side to side 3 or 4 times, and terminating at the top into an ordinary brick chimney; this structure projects into the apartment and is covered with porcelain ware, and the appearance often exhibits great taste and skill, as it will be understood that the structure is not rigidly square, but is often very beautiful from an architectural point of view. The good effect experienced is that after 3 or 4 hours’ firing, the mass of brickwork becomes thoroughly heated and the fire is permitted to go out; communication with the chimney is stopped by means of a damper, and every confidence can then be placed in the stove giving out abundance of warmth for the remainder of the day, as the brickwork takes hours to become moderately cool, and the whole of the heat it contains must be diffused into the apartment. It will be noticed that a minimum of heat is lost by this arrangement, and the result is very satisfactory from an economical standing; but it has not the cheerful appearance of our open fires, and efficient ventilation is required. This plan can, however, be satisfactorily adopted for halls or cold situations; in the former it has the further advantage in most instances of warming the stairways and landings in the upper part of the house by the ascension of the heated air. Fire-brick stoves are made by Doulton & Co., Lambeth, London, and are finished in their majolica and Doulton ware; it is needless to add, these wares give the stoves a very handsome appearance.
Hot-air Furnace.—The close stove is really a hot-air furnace, but it is restricted to heating the air in the room. Other hot-air furnaces are designed to obtain a supply of fresh air and heat it before passing it into the room. The heated air from a fireplace is available to the apartment for only about 12 per cent. of the total amount of heat produced; all the rest passes up the chimney. The close stove, on the contrary, utilises 85-90 per cent. of the heat produced, and loses through the smoke-pipe only about as much as the open fireplace saves—10-15 per cent. And herein lies the striking difference between the relative healthiness of the atmosphere heated by a close stove and an open fireplace. The amount of air which hourly passes through a close stove, heated with a brisk fire, is, on an average, equal to only about 1/10 the capacity of the room warmed, and consequently such stove requires, if unaided, 10 hours to effect a change of the atmosphere in every such apartment. Thus stagnant and heated, the air becomes filled with the impurities of respiration and cutaneous transpiration.
Moisture, too, is an important consideration. The atmosphere, whether within doors or without, can only contain a certain proportion of moisture to each cub. ft., and no more, according to temperature. At 80° F. it is capable of containing 5 times as much as at 32° F. Hence, an atmosphere at 32° F., with its requisite supply of moisture, introduced into a confined space and heated up to 80° F., has its capacity for moisture so increased as to dry and wither everything with which it comes in contact; furniture cracks and warps, seams open in the moulding, wainscoting, and doors; plants die; ophthalmia, catarrh, and bronchitis are common family complaints, and consumption is not infrequent. But this condition of house air is not peculiar to stove-heat. It is equally true of any overheated and confined atmosphere. The chief difference is, that warming the air by means of a close stove is more quickly accomplished and more easily kept up than by any other means. Sometimes, by the scorching of dust afloat in the atmosphere, an unpleasant odour is evolved which is erroneously supposed to be a special indication of impurity, caused by the burning air. It is an indication of excessive heat of the stove. But the air cannot be said to burn in any true sense of the word, for it continues to possess its due proportion of elementary constituents. Such is the close stove and its dangers, under the most unfavourable circumstances.
The essentials for healthy stove-heat are brick-lined fire-chamber, ventilating or exhaust-flue for foul air, means for supplying moisture, and provision for fresh-air supply. A brick lining is requisite for the double purpose of preventing overheating, and for retaining heat in the stove. For the supply of moisture the means are simple and easy of control, but often inadequate. An efficient foul-air shaft may be fitted to the commonest of close stoves by simply enclosing the smoke-pipe in a jacket—that is, in a pipe of 2 or 3 in. greater diameter. This should be braced round the smoke-pipe, and left open at the end next the stove. At its entry into the chimney, or in its passage through the roof of a car, as the case may be, a perforated collar should separate it from the smoke-pipe. For stoves with a short horizontal smoke-pipe, passing through a fire-board, the latter should always be raised about 3 in. from the floor. A smoke-pipe thus jacketed, or fire-board so raised at the bottom, affords ample provision for the escape of foul air.
Hot-air furnaces are simply enclosed stoves placed outside the apartments to be warmed, and usually in cellars or basements of the buildings in which they are used. The manner of warming is virtually the same as by indirect steam heat—by the passage of air over the surface of the heated furnace or steam-heated pipes, as the case may be, through flues or pipes provided with registers. The most essential condition of satisfactory warming by a hot-air furnace is a good chimney-draught, which should always be stronger than that of the hot-air pipes through which the warmed air is conveyed into the rooms, and this can be measured by the force with which it passes through the registers. A chimney-draught thus regulated effectively removes all emanations; for, if the chimney-draught exceeds that of the hot-air pipes, all the gaseous emanations from the inside of the furnace, and if it have crevices, or is of cast iron and overheated, all around it on the outside will be drawn into the chimney. Closely connected with this requirement for the chimney-draught is the regulating apparatus for governing the combustion of fuel—the draught of the furnace. This should all be below the grate; there should be no dampers in the smoke-pipe or chimney, and all joints below and about the grate should be air-tight. The fire-pot should be lined with brick and entirely within the surface, but separate from it, so that the fresh air to be warmed cannot come in contact with the fuel-chamber.
An excellent plan for economising a good portion of the waste heat from a kitchen range is to have (previous to the range being fixed, or after, in some instances) a sheet-iron box or chamber made to fit at the back of the oven flues or wherever the most intense heat is felt. This box, which we may call an air-chamber, should be connected with the outer air, and a pipe for the warm air carried from the top of the box to the part where warmth is required; the heat from the range warms the air in the box and it ascends in exactly the same manner and upon the same principle as a hot-air furnace, but great care must be exercised to see that this box and all connections are made air-tight, or this plan will prove an unusually speedy means of indicating what is being cooked for dinner.
The Americans adopt what is called the “drum” principle of heating by means of a furnace; they not only encase the stove with an air-chamber, but the smoke-pipe is surrounded with a larger pipe encasing it all the way up; the space between the smoke-pipe and the outer pipe is thus an air-chamber and has free connection with the furnace air-chamber, but of course is closed at top; from the chamber surrounding the smoke-pipe, branch pipes are taken to the apartments, terminating in perforated cylindrical “drums,” from which the heated air is emitted.