Chapter VII.THE FIRE-PLACE.
Perhaps no part of the interior fittings of a house is more associated with ideas of cheerfulness and domestic comfort than thefire-place. Our abundant supply of coal has probably induced Englishmen to prefer the cheerful fire and the “comfortable fire-side” to any other mode of heating the interior of houses. The steps by which we have arrived at the use of modern grates and stoves, and the question how far these are likely to give way to the methods of warming houses by hot air, by hot water, or by steam, will form an interesting matter for our consideration; and we shall be indebted toDr.Arnott’s treatise onWarming and Ventilating, for many illustrative details.
The manner in which rude nations kindle a fire in or near their huts, is one of the most wasteful arrangements in which fuel can be used. Houseless savages, because they know no better, and soldiers at bivouac, because they must make a virtue of necessity, kindle a fire in the open air, and place themselves near it, benefiting by that portion of the radiant heat which falls on their bodies; but all the rest of the heat is wastefully dissipated.
The next step of improvement is, to kindle a fire in a place more or less inclosed. Under this arrangement, not only will that part of the radiant heat which falls on the persons be available, but a portion of the remainder also, which, falling on the walls and warming them, is partially reflected; and moreover, heat combined with the smoke will be for a time retained in the place, and thus still further contribute to the warmth of the interior. By such an arrangement, nearly the whole of the heat evolved in the combustion is applied to use; but it is contaminated with the smoke from the fuel. The savages of North America place fires in the middle of the floor of their huts, and sit around in the smoke, of which the excess escapes by the one opening in the hut that serves as a chimney, window, and door. A few of the peasantry in the remote parts of Ireland and Scotland still place their fires in the middle of their floors, and leave for the escape of the smoke only a small opening in the roof, often not directly over the fire. In Italy and Spain, almost the only fires seen in sitting-rooms are large dishes of livecharcoal, or braziers, placed in the middle, with the inmates sitting around, having to breathe the noxious carbonic acid gas which ascends from the fire and mixes with the air of the room: there is no chimney, and the windows and doors are the only ventilators. The method of warming with open fires in the middle of the room was adopted in some of the English Colleges, and some of the London Inns of Court, down to a comparatively modern period.
A step further in advance is to have a fire, not only in an inclosed space as a means of keeping in the heat, but with an aperture over it to act as a chimney or vent for the smoke. This is the form, under various modifications, adopted in most English houses; the fire being kindled in a kind of recess under a chimney. By degrees we have become accustomed to the adoption of agrate, which keeps the fuel at a certain height above the ground; but the principle involved is just the same. In olden times the fire used to be kindled on the hearth under a huge chimney, or on a very low grate; but the general course of modern improvement has tended to lessen the size of the chimney, and to raise the grate higher from the hearth.
The philosophy of a chimney is well explained byDr.Arnott, in hisElements of Physics. He says: “Chimneys quicken the ascent of hot air, by keeping a long column of it together. A column of two feet high rises higher, or is pressed up with twice as much force as a column of one foot, and so, in proportion, for all other lengths; just as two or more corks strung together and immersed in water, tend upwards with proportionally more force than a single cork, or as a long spear of light wood, allowed to ascend perpendicularly from a great depth in water acquires a velocity which makes it dart above the surface, while a short piece under the same circumstances rises very slowly. In a chimney where one foot in height of the column of hot air is one ounce lighter than the same bulk of the external cold air, if the chimney be one hundred feet high, the air or smoke in it is propelled upwards with the force of one hundred ounces. In all cases, therefore, thedraught, as it is called, of a chimney is proportioned to its length.”
This being the general arrangement of a fire in a recess on one side of the room, and an open chimney above it,Dr.Arnott enumerates a long list of evils and inconveniences consequent on such an arrangement.
1.Waste of fuel.—It has been found that in a commonopen English fire, seven-eighths of the heat produced from the fuel ascend the chimney, and are absolutely lost. This lost fuel is thus accounted for. One half of the heat is carried off in the smoke from the burning mass; one quarter is carried off by the current of the warmed air of the room, which is constantly entering the chimney between the fire and the mantel-piece, and mixing with the smoke; lastly, one eighth part of the combustible matter is supposed to form the black and visible part of smoke, in an unburned state. Some writers have even gone so far as to estimate the loss of heat in an open fire at fourteen-fifteenths of the whole. 2.Unequal heating at different distances from the fire.—This forms a remarkable contrast with the uniform temperature in the air of a summer afternoon. In rooms with a strong fire, in very cold weather, it is not uncommon for persons to complain of being “scorched” on one side, and “pierced with cold” on the other; this is particularly the case in large apartments; for as the intensity of radiating heat (like light) is only one-fourth as great at a double distance, the walls of the room farthest from the fire are but little warmed, and, therefore, reflect but little heat to the backs of persons grouped round the fire. 3.Cold draughts.—Air being constantly required to feed the fire, and to supply the chimney-draught, the fresh air which enters by the crevices and defects in the doors, windows, floors, &c., is often felt most injuriously as a cold current. “There is nothing more dangerous to health than to sit near such inlets, as is proved by the rheumatisms, stiff necks, and catarrhs, not to mention more serious diseases, which so frequently follow the exposure. There is an old Spanish proverb, thus translated,
If cold wind reach you through a hole,Go make your will, and mind your soul,
which is scarcely an exaggeration.” The current of fresh air which enters to feed the fire becomes very remarkable when doors or windows are opened, for the chimney can take much more than it otherwise receives when the doors and windows are shut; and thus the room with its chimney becomes like an open funnel, rapidly discharging its warmed air. 4.Cold to the feet.—The fresh air which enters in any case to supply the fire, being colder and specifically heavier than the general mass already in the room, lies at the bottom of this as a distinct layer or stratum, demonstrable by a thermometer, and forming a dangerous cold-bath for the feet of the inmates, often compelling delicate persons to keep their feet raised out of it by footstools, or to use unusual covering to protect them. 5.Bad ventilation.—Notwithstanding the rapid change of airin the room, perfect ventilation is not effected. The breath of the inmates does not tend towards the chimney, but directly to the ceiling; and as it must therefore again descend to come below the level of the mantel-piece before it can reach the chimney, the same air may be breathed over and over again. In a crowded room, with an open fire, the air is for this reason often highly impure. As another source of impure air in a house, it may be noticed that the demand of the chimneys, if not fully supplied by pure air from about the doors and windows, operates through any other apertures. 6.Smoke and dust.—These are often unavoidable from an open chimney, much affecting the comfort and health of the inhabitants of the house, and destroying the furniture. Householders would make great sacrifices in other respects to be free from the annoyance of smoke. In large mansions, with many fires lighted, if the doors and windows fit closely, and sufficiency of air for so many chimneys cannot therefore enter by them, not only do the unused chimneys become entrances for air, but often the longest and most heated of them in use overpower the shorter and less heated, and cause the shorter chimneys to discharge their smoke into the room. 7.Loss of time.—During the time every morning while the fires are being lighted, the rooms cannot be used; and there are, besides, the annoyances of smell, smoke, dust, and noise, all of which are again renewed if the fire is allowed to go out and to be relighted in the course of the day. 8.Danger to person and to property.—How numerous are the losses of property by carelessness as to fires is well known to all, while the loss frequent but more distressing loss of life too well attests the danger to children and to females thinly clad often consequent on an open fire.
Such are the principal defects whichDr.Arnott enumerates as being inherent in the use of open fires. Many of them have been greatly lessened by improved arrangements; but others are still without an appropriate remedy.
The usual construction of a fire-place is tolerably familiar. In most cases, the vertical or nearly vertical channel for the chimney is inclosed within a casing of brick-work, which projects into the room at one side. The opening for this chimney gradually narrows upwards, until only large enough to admit the poor little climbing-boy whose task it was, until within a recent period, to sweep down the unburnt fuel which our own ill arrangements have wasted; but, happily for humanity and justice, this system is at an end, and machines are now employed for the purpose. A hearth of stone is laid whereon to erect the stove or grate, and this grate is, as we all know, composed mainly of an iron receptacle for the fuel,and of “hobs,” for supporting culinary vessels. We cause fire to be kindled in the grate, and then suppose that all will go on well, without troubling ourselves to inquire whether the arrangements for the supply of cold air, and the exit of warmed air and smoke, are such as are best fitted for those purposes.
In course of time, as the evils of this plan became one by one known, attempts were made to remedy some of them, and with an approach towards success. In a recent treatise on the subject byDr.Fyfe, of Edinburgh, various modes are suggested for remedying many of the evils incident to open fire-places. These we must briefly notice.
Sometimes the rooms of a new house are subject to the nuisance of smoky chimneys simply from deficiency of air. The workmanship of the rooms being all good, the joints of the flooring-boards and of the wainscot panels are all true and tight, the more so as the walls, perhaps, not yet thoroughly dry, preserve a dampness in the air of the room, which keeps the wood-work swelled and close. The doors and the sashes, too, work closely and correctly, so that there is no passage left open for the air to enter except the key-hole, and even this is often closed over by a little brass cover. Thus, air being denied admission into the room, there is nothing to feed the fire and to cause a “draught,” and the smoke cannot ascend the chimney. Instances have been known of well-built houses being rendered almost untenantable from this cause, and several hundred pounds being spent in endeavouring to find a remedy. If, on opening the door or window of a smoky room, it be generally found that the smoke disappears, this may be taken as an indication that the close-fitting joints of the wood-work do not admit air enough for the fire when doors and windows are closed. In such a case, the opening of the door or window is a poor attempt at a remedy; for the air proceeds direct to the chimney, and in its way causes cold to the back and feet of those who may be sitting before the fire. Numerous methods have been devised for admitting additional air to the rooms without this inconvenience, among whichDr.Arnott recommends tubes leading directly from the outer air to the fire-place, and provided with what are called “throttle-valves,” for the regulation of the quantity. The following plan has also been recommended as one of the most practicable. As the air in the upper part of a room is warmer than in the lower, it is desirable that the supply should come in that direction, so as tobe slightly warmed in its progress towards the fire, and thus produce less chill to those in its immediate vicinity. This may be done by drawing down the upper sash of the window about an inch; or, if not moveable, by cutting such a crevice through its frame; in both which cases, a thin shelf of the length of the opening may be placed to conceal it, sloping upwards, to direct the air horizontally along and near the ceiling. In some houses, the air may be admitted in such a crevice made in the wainscot or cornice near the ceiling, and over the fire-place; this, if practicable, is the better of the two, since the cold air in entering will there meet with the warmest rising air from before the fire, and be soonest tempered by the mixture. Another contrivance is to take out an upper pane of glass in one of the sashes, set it in a tin frame, giving it two springing angular sides, then replacing it, with hinges below, on which it may turn; by drawing in this pane more or less, the quantity of air admitted may be regulated, and its position will naturally direct the admitted air up and along the ceiling. The circular vane or ventilator sometimes fixed in windows admits cold air in a similar manner, when the supply for the room and fire would be otherwise deficient.
The opening or breadth and height of the fire-place, though we may fancy it leads to the diffusion of more heat into the room, is really a cause of loss of fuel, and of smoke. The size of the fire-place opening is often considered in relation to the size of the room, without regard to the principles on which a fire is maintained in a grate; a course about as rational (it has been well observed) as to proportion the step in a staircase to the height of the story, instead of to the convenience of our legs in mounting them. As the chimneys of different rooms are unavoidably of different heights, and as the force of the draught is in proportion to the height of chimney filled with warmed and rarefied air, it is found that the opening for a tall chimney may be larger than for a lower one. If the opening be unnecessarily large, there is room not only for the entrance of fresh air, but also for the exit of smoke driven down by an opposing current from the chimney itself; and the air, too, ascends into the chimney in too cold a state, because the largeness of the opening enables it to enter without passing very close to the fire. The principal evil attending the use of a fire-place having too small an opening, is that the fuel is burned away with unnecessary rapidity. When the opening is found by experience to be so large as to lead to the descent of smoke into the room, the easiest remedy is to place moveable boards or sheets of tin or iron, so as to lower and narrow it gradually. The effect ofwhich, by excluding a part of the colder air from the chimney, is to produce a quicker action, so that the fire begins to roar as if blown by a bellows. “This means is often used to blow the fire instead of bellows, or to cure a smoky chimney, by increasing the draught. What is called aregister stoveis a kindred contrivance. It has a flap placed in the throat of the chimney, which serves to widen or contract the passage at pleasure. Because the flap is generally opened only enough to allow that air to pass which rises directly from the fire, the chimney receives only very hot air, and therefore acts well. The register stove often cures smoky chimneys; and by preventing the too ready escape of the moderately warmed air of the room, of which so much is wasted by a common fire-place, it also saves fuel.” There does not appear to have been any attempt to determine by experiment the proper opening of the fire-place for a given height of chimney; and, indeed, there are so many disturbing causes, that it would be scarcely possible to determine this with precision.Dr.Franklin, however, proposed to make the fire-place openings in the lower rooms about thirty inches square and eighteen inches deep; those in the upper, eighteen inches square, and not quite so deep; and those in the intermediate rooms, of dimensions between these two extremes.
In some cases, where other matters are properly attended to, inconvenience results from the chimney being too low; as, for instance, in the case of an attic chimney. In this instance the column of heated and rarified air is not high enough to give a rapid ascensive power within the chimney, and thus the smoke cannot be carried up. The best method of cure is to add to the length of chimney, if this can be done, and if the fire be in a low building near the ground, this may perhaps be effected; but in an attic, the means of supporting a lofty chimney would be inefficient. Another recourse is to contract the opening of the fire-place to the smallest available dimensions, so that all the entering air may pass through or close to the fire before entering the chimney, and thus acquire an ascensive power which will counterbalance the shortness of the vertical column. It has been recommended that in some cases there may be three chimneys to one room, so that the united length of the whole may be equal to that of a tall chimney; but it is not easy to conceive how this can be practically effected, nor how the desired result would follow, even if the arrangements were made. In some cases, the chimney of a room is rendered practically shorter by being bent round and made to enter the chimney of another room; since, unless there be a fire in this room also, the warm airfrom the shorter chimney has often an adverse current to contend against at the junction with the other chimney. This is one reason why every open fire-place should have its own chimney independently of others.
If there be a lofty building or hill near a house, and over-topping the chimney of one of the rooms, that room is very likely to become smoky, on account of a current being driven in at the top of the chimney, and forcing the smoke down with it. Two rival chimneys may produce a similar effect in a remarkable way. Suppose that there were two fires in one room, one burning with more force, and therefore having a more ascensive column of air above it, than the other; if the doors and windows be shut, the stronger fire will overpower the weaker, and for its own demand will draw down air from the chimney of the latter, which air in descending brings down smoke into the room. The same would be observable in a greater degree if one fire-place had a fire in it but the other had none, both being at the same time open. If, instead of being in one room, the chimneys are in two different rooms communicating by a door, the case is the same whenever that door is open. In a house where all the openings, such as doors and windows fitted tightly, a kitchen chimney has been known to overpower every other chimney in the house, and to draw air and smoke into an upper room as often as the door communicating with the room was open. The remedy for this inconvenience lies in the arrangement of the fire-places, so that each fire shall have exactly enough air for the consumption of the fuel, without having to borrow from other rooms.
The arrangement of the door of a room influences materially the proper action of a fire in the fire-place. When the door and chimney are on the same side of the room, and if the door be in the corner, and is made to open against the wall, (an arrangement which is often made for the sake of convenience,) it follows, that when the door is only partly opened, a current of air rushes along the wall into and across the opening of the fire-place, and drives some of the smoke out into the room. This acts more certainly when the door is being closed, for then the force of the current is augmented, and becomes an annoyance to persons who may happen to be situated in its path. When the door and fire-place of a room have been thus ill-arranged with respect to each other, the evil may be lessened by placing an intervening screen between the door and the fire, or by reversing the position of the hinges on the door, so as to make it open in the opposite direction.
Sometimes the smoke from a chimney is driven out into theroom, even when the chimney is not commanded by a superior elevation, it being driven down by strong winds passing over the top of the chimney.Dr.Franklin mentioned one or two instances of this kind which he had met with:—“I once lodged at a house in London, which in a little room had a single chimney and funnel. The opening was very small, yet it did not keep in the smoke, and all attempts to have a fire in this room were fruitless. I could not imagine the reason, till at length observing that the chamber over it, which had no fire-place in it, was always filled with smoke when a fire was kindled below, and that the smoke came through the cracks and crevices of the wainscot, I had the wainscot taken down, and discovered that the funnel which went up behind it had a crack many feet in length, and wide enough to admit my arm; a breach very dangerous with regard to fire, and occasioned probably by an apparent irregular settling of one side of the house.” This does not at first thought seem to be an illustration of the effect of wind passing over the top of a chimney; but the explanation is to be sought for in a similar way; the air, by entering this fractured part freely, destroyed the drawing-force of the chimney.
The manner in which the passing of a current of wind over the top of a chimney may produce a “smoky room” is this:—the warm air which rises from the fire, in order to obtain a free issue from the chimney, must repel the air that is hovering over the chimney-pot. In a time of calm or of little wind, this is done easily; but when a violent current is passing over the top of the chimney, its particles have such a strong horizontal velocity, that the heated air in ascending has not power to displace it, and thus the smoke, not finding a ready exit by that path, is driven back into the room.
The following anecdote, told byDr.Franklin, will show what accidental causes will sometimes occasion a fire to fail in its desired office of yielding heat without smoke:—“Another puzzling case I met with at a friend’s house near London. His best room had a chimney, in which he told me he never could have a fire, for all the smoke came out into the room. I flattered myself I could easily find the cause, and prescribe the cure. I opened the door, and perceived it was not want of air. I made a temporary contraction of the opening of the chimney, and found that it was not its being too large that made the smoke to issue. I went out and looked up at the top of the chimney: its funnel was joined in the same stack with others, some of them shorter, that drew very well, and I saw nothing to prevent its doing the same. In fine, after every other examination I could think of, I was obliged to own the insufficiency of my skill. But my friend, who madeno pretension to such kind of knowledge, afterwards discovered the cause himself. He got to the top of the funnel by a ladder, and looking down, found it filled with twigs and straw, cemented by earth, and lined with feathers. It seems the house, after being built, had stood empty some years before he occupied it, and he concluded that some large birds had taken the advantage of its retired situation to make their nests there. The rubbish, considerable in quantity, being removed, and the funnel cleared, the chimney drew well and gave satisfaction.”
From these details it will at once appear, that that part of the builder’s art which relates to the arrangement and building of the fire-place is by no means an unimportant one, since the comfort of the inmates is seriously affected by want of skill on his part. Hence we may also observe, that chimney doctors are liable to the same kind of errors as quack doctors in another sphere; for it is almost as absurd to attempt to cure all smoky chimneys by one course of proceeding, as to cure all kinds of diseases by one medicine. There may be a deficiency of air in the room; the opening of the fire-place maybe too large; the chimney may not have height enough; one chimney may overpower another in its draught; the chimney may be overtopped by higher buildings or by a hill; the door of a room may be badly placed with respect to the window; or, lastly, as inDr.Franklin’s “puzzling case,” the chimney may be nearly stopped up. All these are sources of the much-dreaded “smoky chimney,” and all require modes of treatment adapted to the nature of the evil. Many of these evils have, to a considerable extent, been remedied by the use of Rumford stoves, and other forms of stove and grate, in which, although retaining all the chief characters of an open fire-place, there is yet a great diminution of the evils to which the latter is liable. There have, however, been marked extensions recently made in the construction ofclose stoves, intended to obviate the ill effects attendant on open fire-places. These must be briefly noticed.
In a close stove, no air is admitted but what passes at once through the fire; and the chimney or funnel is only just large enough to carry off the sulphurous and other vapours, for there is hardly any smoke from a close stove, and, therefore, it is not necessary to make a chimney large enough to admit a climbing-boy.
A small German stove, suitable for a room twenty-four feet by eighteen, will give an idea of the general character of thiskind of close stove. The stove rests on a base about thirty-six inches by fourteen. The fire-place has a bottom to receive the fuel, but no bars, and is shut by a door which fits closely to its case. This door has a small wicket at the bottom, the aperture of which is regulated by a sliding plate, so as to admit no more air than will suffice for the slow combustion of the fuel. The flame and heated air ascend to the top of the fire-place, and pass into two hollow pillars or piers, which rise to a height of five or six feet, so that the heat is communicated to a large surface, before the volatilized products of combustion make their exit by a pipe into the chimney. The stove is supplied with fuel and with air by the front door. If it is desired to make the fire visible, and impart some of that cheerfulness which belongs to an open grate, the door of the stove maybe thrown open, for there is no danger of the smoke coming out after the current has once warmed the upper part of the stove. When the stove is of such dimensions that the body of it is about two feet and a half high, the fire-place may be furnished with a small grate in the English style. If the door is so hung that it can not only be thrown back, but also lifted off its hinges, it will approach still more to the character of a stove-grate.
A cheap form of “German stove” is often made in this country, and used in workshops and small manufactories, where the body of the stove is an upright cylinder, of which the lower part is the ash-pit, closed or opened by a hinged-door, the middle part the fire-place, where the fuel rests on bars, and the upper part a vacant space, which becomes filled with flame, smoke, and heated air, so as to impart great heat to a flat iron plate at the top. There is a door at which the fuel is introduced, and a small flue or funnel of iron pipe, which conveys the smoke into a chimney or into the open air. Many forms of stove have been used more or less resembling this in principle; but there is one great defect pertaining to them all. The metal of which the stove is formed becomes so highly heated near the stove, that it acquires aburntsmell, owing to the decomposition of animal and vegetable particles which are at all times floating about in the air. The air, too, in the room, becomes close and oppressive from another cause; for as only a small quantity of air is consumed by the stove, the air does not become renewed in the room so frequently as when an open fire is used, and thus it is respired over and over again.
To remedy the evils resulting from burnt air, close stoves are made with a double case, so that there shall be a body of air between the fire and the air of the room. It is on this principle, modified in various ways, that a large numberof stoves have been constructed; of which one, byMr.Sylvester, may be briefly described. There is a hollow cast-iron box, on the outside of which are cast several ribs. Those ribs are about three-quarters of an inch thick, and project three or four inches beyond the surface of the box; and their object is to increase the heating surface; for the fire being lighted in the hollow of the box, the conducting power of the iron causes the whole exterior case of the box, together with the projecting ribs, to become heated. The box is placed within an ornamental case, the sides and top of which are fretted with lattice-work, to allow free access to the air, which enters through the lattices at the sides and escapes from the top of the stove, passing in its passage over the ribbed surface of the heated box. The grating on which the fuel lies is formed of a number of loose bars fitted together into a frame, and prolonged so as to emit heat into the room as well as to support the fuel. Everything is so arranged as to give as much iron surface as possible, so as to communicate heat to the surrounding air; while at the same time the extent of the heated surface prevents any one part from being excessively and injuriously heated.
To describe all the “chunk” stoves, “Vesta” stoves, “Olmsted” stoves, and other similar contrivances of modern times, would fill a volume instead of a few pages. We may, however, speak briefly ofDr.Arnott’s stoves as a means of showing some of the inconveniences to which close stoves are liable, if not constructed with care. This stove consists of an external case of iron, of any ornamental shape. Within this case is placed a box made of fire-clay, to contain the fuel, having a grating at the bottom; and there is a space left between the fire-box and the exterior case, to prevent the communication of too much heat to the latter. Thee pedestal of the stove forms the ash-pit; and there is no communication between the stove and the ash-pit, except through the grating at the bottom of the fire-box. A small external hole in the ash-pit, covered by a valve, admits the air to the fire; and according as this valve is more or less open, the vividness of the combustion is increased or diminished, and thence the greater or less heat produced by the stove. The quantity of air admitted by this valve is governed by a self-regulating apparatus, either by the expansion and contraction of air confined by mercury in a tube, or by the unequal expansion of different metals. The smoke escapes through a pipe at the back of the stove; but the fuel employed is such as toyield very little smoke. By adjusting the regulator so as to admit only a small quantity or air, the temperature of the stove is kept within the required limits; and owing to the slow-conducting power of the fire-clay, of which the fire-box is formed, the heat of the fuel is concentrated within the fire-box, and the fuel burns with less air and less rapidity than it would otherwise do.
The construction ofDr.Arnott’s “thermometer stove” will be better understood from the following figure, which represents the stove with one of its sides removed, so as to exhibit its interior arrangements:—
Diagram of thermometer stove
The outlines of the figure,a a a a, represent the case or body of the stove, which might be formed either of cast or sheet iron. It is divided into two chambers by the partition,b b; but in such a way that there may be a free communication at the top and bottom.cis a small furnace, or, as it is called by the inventor, a fire-box, made of iron, and lined with fire-bricks. The fire-box is not in contact with the exterior case of the stove. It communicates at the bottom with an ash-pit, the door of which is atd,—that of the stove, by which the fuel is introduced, is atd´. Both these doors must fit very accurately. Above the door of the ash-pit is a bent pipee, by which air gains admittance to the fire.
A fire being kindled and the doors atd d´shut, the only way in which air has access to the fuel is by the pipee; the air so admitted, passing through the fire before it enters the upper part of the stove. That portion of the air not requiredto aid the combustion of the fuel having reached the main body of the stove, and there mixing with the smoke and other products, they circulate slowly in the directions indicated by the arrows, and at length pass into the chimney by the pipef.
The slow movement just mentioned as taking place within the stove may well be contrasted with what happens in an open fire-place. In one case the greater part of the heat produced is rapidly carried off by a current of air ascending the chimney—by the thermometer stove it is detained until almost the whole of it has been diffused throughout the apartment.
The bent tubegterminating in a cup-shaped opening atg´, is a self-regulating valve. The tube is closed at the endgwithin the stove,g´ g´´represents mercury which occupies the bend of the tube. When the fire in the stove burns too briskly, the air in the tube occupying the space betweengandg´´is expanded, and by expelling some of the mercury from the tube atg´´into the cup atg´, it closes the aperture of the pipee; thus cutting off the supply of air to the fire. In a few minutes (the fire in the mean time having abated its energy,) the air in the tube will return to its former dimensions, and the mercury subsiding in the cup, air is again permitted to enter the ash-pit.
The stove, of which we have thus attempted to convey a general idea, may be made of any required form or size. Instead of the self-regulating air-valve just described, it is fitted up with others of a very simple construction, and which admit of being adjusted with the greatest accuracy by the hand.
The objections to this form of stove arise chiefly from the formation of deleterious gases, which are not carried off completely. The slow combustion of the fuel produces a large quantity of carbonic oxide, which is liable to escape into the room, and is of an injurious character. Carburetted hydrogen gas is also formed in these stoves. Many modifications of form have been suggested for the remedy of these evils; but the slow combustion, which was one of the merits originally claimed for the stove, and which it certainly deserves, seems an unavoidable cause for the production of these gases.
All the varieties of open fire-place, as adopted in English houses, the hearth, the recess, and the chimney, are at one side or at one corner of the room; but in the adoption of close stoves this arrangement is not necessary; for the stove may be in any part of the middle of a room, provided the pipe constituting the flue be long enough. In some cases this pipe is carried upwards to the ceiling, and thence conveyed tosome outlet into the open air; in other cases it is turned downwards and conveyed under the flooring to a proper place of exit; while in others the pipe is stretched or extended horizontally from the stove to the regular chimney of the room.
Our builders have not yet entered so far into the mechanical contrivances of the age as to dispense with chimneys altogether; nor could such a thing be done until a total change is effected in the opinion of persons concerning the cheerfulness of an “open fire.” But there are nevertheless three modes, more or less adopted in the present day, whereby a house is warmed without the necessity for anything like a fire-place. These methods—in all of which the heating agent is brought from another room into the one to be warmed—are of three kinds; heating byhot air, byhot water, and bysteam.
When we speak of warming an apartment by heated air, it is necessary to give precision to the meaning of the term. All rooms are, in fact, warmed by heated air, for the stove or grate must raise the temperature of the air in the room before we can appreciate the sensation of warmth. But what is generally meant by the term as here used is the warming of one apartment by air heated in another. The stoves used in Russia, though not coming exactly under this description, will serve in some degree to illustrate the principle.
The Russian stove is intended as a sort of magazine, in which a great quantity of heat maybe quickly accumulated, to be afterwards slowly communicated to the apartment. The stove is therefore made of a massive size. It is formed of brick-work, clay, glazed tiles, which together form a great mass of matter to be heated by the fuel; and there is in every part a considerable thickness of slow-conducting material between the fuel and the air of the room. The fire is kindled early in the morning, after which the stove door is shut, and the air aperture below left open for some time as a means of admitting draught to the fire; but in the course of a short time the fire-door is opened to check the draught, so as to prevent the too rapid combustion of the fuel. In this way the combustion is allowed to go on, and the substance of the stove becomes warmed, after which the air passages are shut, so as to prevent any abstraction of heat by the current that would otherwise be occasioned. The stove thus becomes a great mass of heated matter, which is gradually pouring warmth into the apartment during the whole of the day; and as the temperature of the surface never becomes very high,the impurities in the atmosphere are not decomposed, and it is consequently free from those offensive effluvia, unavoidable when metal stoves are used. The fuel is allowed to be nearly burnt out before the apertures of the stove are closed; and therein the stove differs greatly from those hitherto considered; the heated air within the stove being so completely shut in that it can find no outlet, except through the substance of the brickwork.
The modifications of the arrangements whereby warmed air is conveyed from one room to another, may next be noticed. In such cases the air either escapes from a heated receptacle outside the fire-case, or else it merely passes over a heated metallic surface. The following description relates to one variety of the first of these two methods. In the lower part of a house or building is a cast-metal double stove; the inner part forming the stove, and the outer one the case or envelope. The fuel is burned in the inner stove, and the smoke produced during the process of combustion is carried off by a chimney, which passes through both stoves or cases, and is conveyed to the outside of the building. The outer case includes not only the furnace or inner stove, but also a considerable space occupied by the air of the atmosphere, which is freely admitted through a number of holes placed around it; and when any current of warmed air is produced, it passes off from the space between the outer case and the inner stove, and is conveyed by tubes to any apartment in the building; so that the rooms are warmed by the air which has passed between the outer case and the inner stove.
In another form of arrangement, having the same end in view by means of heated air, the air, instead of passing through an enclosed space between the outer case and the inner stove, passes over a surface of metal which is heated either by a fire underneath, or, which is better, by steam or hot water contained in pipes. The temporary House of Commons, the Reform Club-house, and many other buildings, are warmed in this way.
The following simple and cheap form of stove has been erected in the cottages of Sir Stewart Monteath’s labourers. The accompanying figure represents a section of the stove, the principle of which will be understood from the following explanatory notes:—
Section of a stove
Kitchen fire.Chimney.Hot air Chamber.This is a cast-iron box, which forms the back of the kitchen grate.Cold air pipe, or passage; made with brick, or stone, or iron piping, communicating with the open air for the purpose of feeding the hot air chamber with an ascending current of fresh air.Hot air pipe, receives the ascending current of air, which becomes heated by passing over the back of the fire. At the top this pipe branches off at right angles, and terminates near the floor in the two sleeping rooms above.Gratingsto admit the warm air from the hot-air pipe into the bed-rooms. The addition of sliding valves over the face of the gratings would serve to cut off the current of warm air during the summer, and when not otherwise required.Sitting-room, into which sufficient heat is radiated from the hot air chamber, not only to warm the apartment, but even to dry wet linen.
By means of one common fire in a stove of the above description, a four-roomed cottage can be comfortably warmed, and kept dry throughout.
The arrangements for warming rooms and buildings by steam are very different from those in which stoves are employed. They are generally such as the following. At a convenient part of the building, and as low as possible, there is placed a close steam-boiler of the ordinary construction. From this boiler a small steam-pipe is carried to the parts of the building which are to be warmed; the pipe being wrapped round with a thick layer of flannel, to prevent the heat from radiating before it arrives at the destined place. Pipes of a larger size are laid round the rooms above the floor, or under a perforated floor, or in any other convenient position. The steam issues into these larger pipes, from the surface of which heat radiates into the room, and thus the steam is condensedinto water. Small pipes of lead or tin are provided for convoying the water back into the boiler, a gentle slope being given to all the pipes to facilitate this object. This water, again flowing into the boiler, is again converted into steam, again ascends to the pipes which surround the apartment, again gives out heat to the air of those apartments, and again flows back to the boiler in the form of water. Thus the same supply of water circulates over and over again through the pipes, carrying heat from the fire below to the rooms above. In some cases the steam-pipes in the apartments, instead of being laid round the sides, are grouped together in a compact form, and have an ornamental character imparted to them.
Instead of pipes, the steam is sometimes made to circulate between parallel sheets of copper or iron, in such manner that every sheet of metal shall have steam on one side of it, and air on the other, the air in that position receiving heat from the steam through the metal.
Lastly we have to notice the method of warming byhot water. In this method there is usually a boiler communicating by an upper and lower pipe, with an upright pipe the same height as the boiler. On the application of heat to the boiler, the column of water becomes lighter than that in the upright pipe; therefore the pressure on the water in the lower pipe being less at the end nearest to the boiler than it is at the other end, a portion of the water in this lower pipe moves forward towards the boiler, which causes a corresponding quantity to pass along the upper pipe in a contrary direction. This motion will necessarily continue as long as the column of water in the boiler is hotter, and therefore lighter than that in the upright pipe; and this must be the case so long as the boiler continues to receive heat from the fire, and the pipes to part with their heat to the air, and thereby cool the water contained in them. In whatever form the hot water apparatus is constructed, this difference of pressure of the two columns of water is the cause of the circulation.
In this form of apparatus some part or other of the water is open to the atmosphere, either at the top of the boiler or at the top of one of the pipes, so that there is no danger from the bursting action of water heated above the boiling temperature. But, on the other hand, the water cannot well be conveyed to rooms at different elevations in the building. To increase the efficacy of the arrangement in this respect, the following adaptation has been suggested. A pipe is made to dip into an open boiler, reaching only an inch or two belowthe surface of the water, and passing round the room to be warmed, returns again to the boiler and dips again into the water, descending quite to the bottom of the boiler. An air-pump is connected with this pipe by a small tube; and the air in the pipe being exhausted by this means, the water rises into the pipes above the level of the boiler by atmospheric pressure, and the circulation then takes place by the hot water ascending through the pipe at the top of the boiler, and passing through the whole circuit of the pipe, it returns through the upper end of the pipe which reaches to the bottom of the boiler.
In the last-described form of apparatus the water will rise in the syphon pipe to a height of about thirty feet above the boiler, being that elevation which is due to the action of the atmosphere on liquid flowing through a vacuum. But when a whole house or building is warmed by hot water in all the different floors or heights, a modification of the system, called thehigh-pressure system, is adopted.
The apparatus on this system consists of a spiral coil of small iron pipe built into a furnace, the pipe being carried from the upper part of the coil, and entwined round the room intended to be warmed, forming a continuous pipe when again joined to the bottom of the coil. The size of the pipe is usually only half an inch in diameter internally, and an inch externally. A large pipe of about two and a half inches diameter is connected, either horizontally or vertically, with the small pipe, and is placed at the highest point of the apparatus. This, which is called the “expansion pipe,” has an opening near its lower extremity, by which the apparatus is filled with water, the aperture being afterwards secured by a strong screw; but the expansion pipe itself cannot be filled higher than this opening. After the water has been introduced, the screw is securely fastened, and the apparatus becomes completely closed in all parts. The expansion pipe, which is thus left empty, is calculated to hold about one-tenth or one-twelfth as much water as the whole of the small pipes; this being necessary in order to allow for the expansion that takes place in the volume of the water when heated, and which otherwise would inevitably burst the pipes, however strong they might be.
In this apparatus the principle of action is different from that in the low-pressure method. Here the water is raised to so high a temperature that it wholly overcomes the effect of gravity, and rises to the highest rooms of a building if required, the circulation through the system of pipes being more rapid as the heat of the water is greater. But there are inconveniences attending the method. If the pipes benot very strong, they will be burst by the intense pressure from within; as they will likewise if the expansion pipe be too small. If, on the contrary, this latter pipe be too large, it occasions the water to be driven up into it so violently as to leave the lower part of the coil of small pipe almost empty, and therefore liable to be burned by the heat of the fire. And if all these points be properly attended to, there is still the inconvenience resulting from the decomposition of the floating particles in the air, by the highly-heated metal of the pipes. In some cases water, instead of being heated in a coil of small pipes, passes into and through large flat boxes or chambers, whose extended surface enables the surrounding air to be heated more rapidly.
The details of this chapter will enable the reader to perceive, that that part of the builder’s art which relates to the construction of thefire-placerests on more scientific principles, and is more liable to change by successive discoveries and inventions, than most others. It is not simply to make a square opening by the side of a room, to have a vertical chimney or flue above that opening, and a few bars within it; it is not by such means that the object to be answered by a fire-place can be attained; some knowledge of chemistry, pneumatics, and hydraulics, is required before we can properly regulate the combustion of our fuel, the ventilation of our apartments, or effectually warm them by the ascension of hot air, the circulation of hot water, or the condensation of steam.