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The plague of a smoking chimney is proverbial, and has engaged considerable attention from observers of various descriptions. Smoky chimneys in a new house, are such, frequently, for want of air. The workmanship of the rooms being all good and just out of the workman's hands, the joints of the flooring and of the pannels of the wainscoting 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 woodwork swelled and close: the doors and the sashes too being worked with truth, shut with exactness, so that the room is perfectly tight, no passage being left open for the air to enter except the key-hole, and even that is frequently closed by a little dropping shutter.

In this case it is evident that there can be no regular current through the flue of the chimney, as any air escaping from its aperture would cause an exhaustion in the air of the room similar to that in the receiver of an air-pump, and therefore an equal quantity of air would rush down the flue to restore the equilibrium; accordingly the smoke, if it ever ascended to the top, would be beat down again into the room. Those, therefore, who stop every crevice in a room to prevent the admission of fresh air, and yet would have their chimney carry up the smoke, require inconsistencies and expect impossibilities. The obvious remedy in this case is, to admit more air, and the question will be how and where this necessary quantity of air from without is to be admitted, so as to produce the least inconvenience; for if the door or window be left so much open, it causes a cold draft of air to the fire-place, to the great discomfort of those who sit there. 

Various have been the contrivances to avoid this, such as bringing in fresh air through pipes in the jambs of the chimney, which, pointing upwards, should blow the smoke up the funnel; opening passages in the funnel above to let in air for the same purpose; but these produce an effect contrary to that intended, for as it is the constant current of air passing from the room through the opening of the chimney into the flue, which prevents the smoke coming out into the room, if the funnel is supplied by other means with the air it wants, and especially if that air be cold, the force of that current is diminished, and the smoke in its efforts to enter the room finds less resistance. The wanted air must then indispensably be admitted into the room to supply what goes off through the opening of the chimney, and it is advisable to make the aperture for this purpose as near the ceiling as possible, because the heated air will naturally ascend and occupy the highest part of the room, thus causing a great difference of climate at different heights, a defect which will be in some measure obviated by the admission of cold air near the ceiling, which descending, will beat down and mingle the air more effectually. 

Another cause of smoky chimneys is too short a funnel, as, in this case, the ascending current will not always have sufficient power to direct the smoke up the flue. This defect is frequently found in low buildings, or the upper stories of high ones, and is unavoidable, for if the flue be raised high above the roof to strengthen its draft, it is then in danger of being blown down and crushing the roof in its fall. The remedy in this case is to contract the opening of the chimney so as to oblige all the entering air to pass through or very near the fire, by which means it will be considerably heated, and by its great rarefaction, cause a powerful draft, and compensate for the shortness of its column. The case of too short a funnel is more general than would be imagined, and often found where one would not expect it; for it is not uncommon in ill-contrived buildings, instead of having a separate funnel for each fire-place, to bend and turn the funnel of an upper room so as to make it enter the side of another flue that comes from below. By this means the funnel of the upper room is made short, of course, since its length can only be reckoned from the place where it enters the lower funnel, and that flue is also shortened by all the distance between the entrance of the second funnel and the top of the stack; for all that part being readily supplied with air through the second flue, adds no strength to the draft, especially as that air is cold when there is no fire in the second chimney. 

The only easy remedy here, is to keep the opening shut of that flue in which there is no fire. Another very common cause of the smoking of chimneys is, their overpowering one another. For instance, if there be two chimneys in one large room, and you make fires in both of them, you will find that the greater and stronger fire shall overpower the weaker, and draw air down its funnel to supply its own demand, which air descending in the weaker funnel will drive down its smoke, and force it into the room. If, instead of being in one room, the two chimneys are in two different rooms communicating by a door, the case is the same whenever that door is open. The remedy is, to take care that every room have the means of supplying itself from without, with the air its chimney may require, so that no one of them may be obliged to borrow from another, nor under the necessity of lending. 

Another cause of smoking is, when the tops of chimneys are commanded by higher buildings, or by a hill, so that the wind blowing over such eminences falls like water over a dam, sometimes almost perpendicularly on the tops of the chimneys that lie in its way, and beats down the smoke contained in them. The remedy commonly applied in this case is, a turn-cap, made of tin or plate-iron, covering the chimney above, and on three sides, open on one side, turning on a spindle, and which being guided or governed by a vane, always presents its back to the wind. This method will generally be found effectual, but if not, raising the flues, where practicable, so as their tops may be on a level with or higher than the commanding eminence, is more to be depended on. There is another case of command, the reverse of that last mentioned; it is where the commanding eminence is farther from the wind than the chimney commanded. For instance, suppose the chimney of a building to be so situated as that its top is below the level of the ridge of the roof, which, when the wind blows against it, forms a kind of dam against its progress. In this case, the wind being obstructed by this dam, will, like water, press and search for passages through it, and finding the top of the chimney below the top of the dam, it will force itself down that funnel in order to get through by some door or window open on the other side of the building, and if there be a fire in such chimney, its smoke is of course beat down and fills the room. 

The only remedy for this inconvenience is, to raise the funnel higher than the roof, supporting it, if necessary, by iron bars; for a turn-cap in this case has no effect, the dammed up air pressing down through it in whatever position the wind may have placed its opening. Chimneys otherwise drawing well are sometimes made to smoke by the improper and inconvenient situation of a door. When the door and chimney are placed on the same side of a room, if the door is made to open from the chimney, it follows, that when only partly opened, a current of air is admitted and directed across the opening of the chimney, which is apt to draw out some of the smoke. Chimneys which generally draw well, do, nevertheless, sometimes give smoke into the room, it being driven down by strong winds passing over the tops of their flues, though not descending from any commanding eminence. To understand this, it may be considered that the rising light air, to obtain a free issue from the funnel, must push out of its way, or oblige the air that is over it to rise. In a time of calm, or of little wind, this is done visibly; for we see the smoke that is brought up by that air rise in a column above the chimney. 

But when a violent current of wind passes over the top of a chimney, its particles have received so much force, which keeps them in a horizontal direction, and follow each other so rapidly, that the rising light air has not strength sufficient to oblige them to quit that direction, and move upwards to permit its issue. Add to this, that some of the air may impinge on that part of the inside of the funnel which is opposed to its progress, and be thence reflected downwards from side to side, driving the smoke before it into the room. The simplest and best remedy in this case is the application of a chimney-pot, which is a hollow truncated cone of earthenware placed upon the top of the flue. The intention of this contrivance is, that the wind and eddies which strike against the oblique surface of these covers may be reflected upwards instead of blowing down the chimney. The bad construction of _fire-places_ is another cause of smoking chimneys; and this case will lead us to the consideration of the methods of increasing the heat and diminishing the consumption of fuel; for it will be found that the improvements necessary to produce the last-mentioned end will also have a general tendency to cure smoky chimnies. On this subject the meritorious labors of Count Rumford are conspicuous, and we shall proceed to give an abridged account of his method. 

In investigating the best form of a fire-place, it will be necessary to consider, first, what are the objects which ought principally to be had in view in the construction of a fire-place; and, secondly, to consider how these objects can best be attained. Now the design of a chimney-fire being simply to warm a room, it is essential to contrive so that this end shall be actually attained, and with the least possible expense of fuel, and also that the air of the room be preserved perfectly pure and fit for respiration, and free from smoke and all disagreeable smells. To cause as many as possible of the rays, as they are sent off from the fire in straight lines, to come directly into the room, it will be necessary, in the first place, to bring the fire as far forward, and to leave the opening of the fire-place as wide and high as can be done without inconvenience; and secondly, to make the sides and back of the fire-place of such form, and of such materials, as to cause the direct rays from the fire which strike against them, to be sent into the room by reflection in the greatest abundance. Now, it will be found, upon examination, that the best form for the vertical sides of a fire-place, or the _covings_, as they are called, is that of an upright plane, making an angle with the plane of the back of the fire-place of about 135 degrees. 

According to the old construction of chimneys, this angle is 90 degrees, or forms a right angle; but, as in this case the two covings are parallel to each other, it is evident that they are very ill contrived for throwing into the room, by reflection, the rays from the fire which fall on them. The next improvement will be to reduce the throat of the chimney, the immoderate size of which is a most essential fault in their construction; for, however good the formation of a fire-place may be in other respects, if the opening left for the passage of the smoke is larger than is necessary for that purpose, nothing can prevent the warm air of the room from escaping through it; and whenever this happens, there is not only an unnecessary loss of heat, but the warm air, which leaves the room to go up the chimney, being replaced by cold air from without, produces those drafts of air so often complained of. But though these evils may be remedied, by reducing the throat of the chimney to a proper size, yet, in doing this, several considerations will be necessary to determine its proper situation. As the smoke and hot vapour which rise from a fire naturally tend upwards, it is evident that it will be proper to place the throat of the chimney perpendicularly over the fire; but to ascertain its most advantageous distance, or how far above the burning fuel it ought to be placed, is not so easy, and requires several advantages and disadvantages to be balanced. 

As the smoke and vapour rise in consequence of their being rarefied by heat, and made lighter than the air of the surrounding atmosphere, and as the degree of their rare-fraction is in proportion to the intensity of their heat, and as this heat is greater near the fire than at a distance from it, it is clear, that the nearer the throat of a chimney is to the fire, the stronger will be what is commonly called its draught, and the less danger there will be of its smoking, or of dust coming into the room when the fire is stirred. But, on the other hand, when a very strong draught is occasioned by the throat of the chimney being very near the fire, it may happen that the influx of air into the fire may become so strong as to cause the fuel to be consumed too rapidly. This however will very seldom be found to be the case, for the throats of chimnies are in general too high. In regard to the materials which it will be most advantageous to employ in the construction of fire-places, little difficulty will attend the determination of that point. As the object in view is to bring radiant heat into the room, it is clear that that material is best for the construction of a fire-place which reflects the most, or which absorbs the least of it, for that heat which is absorbed cannot be reflected. 

Now, as bodies which absorb radiant heat are necessarily heated in consequence of that absorption; to discover which of the various materials that can be employed for constructing fire-places are best adapted for that purpose, we have only to find, by an experiment very easy to be made, what bodies acquire least heat, when exposed to the direct rays of a clear fire; for those which are least heated evidently absorb the least, and consequently reflect the most radiant heat. And hence it appears that iron, and in general metals of all kinds, which are well known to grow very hot when exposed to the rays projected by burning fuel, are to be reckoned among the very worst materials that it is possible to employ in the construction of fire-places. Perhaps the best materials are fire-stone and common bricks and mortar. These substances are fortunately very cheap, and it is not easy to say to which of the two the preference ought to be given. When bricks are used, they should be covered with a thin coating of plaster, which, when perfectly dry, should be white-washed. The fire-stone should likewise be white-washed, when that is used; and every part of the fire-place which does not come into actual contact with the burning fuel should be kept as white and clean as possible. The bringing forward of the fire into the room, or rather bringing it nearer to the front of the opening of the fire-place, and the diminishing of the throat of the chimney, being two objects principally had in view in the alterations of fire-places recommended, it is evident that both these may be attained merely by bringing forward the back of the chimney. It will then remain to be determined how far the back should be brought forward. This point will be limited by the necessity of leaving a proper passage for the smoke. Now, as this passage, which in its narrowest part is called the throat of the chimney, ought, for reasons before stated, to be immediately or perpendicularly over the fire, it is evident that the back of the chimney should be built perfectly upright. 

To determine therefore the place of the new back, nothing more is necessary than to ascertain how wide the throat of the chimney ought to be left. This width is determined by Count Rumford from numerous experiments, and comparing all circumstances, to be four inches. Therefore, supposing the breast of the chimney, or the wall above the mantle, to be nine inches thick, allowing four inches for the width of the throat, this will give thirteen inches for the depth of the fire-place. The next consideration will be the width which it will be proper to give to the back. This, in fire-places of the old construction, is the same with the width of the opening in front; but this construction is faulty, on two accounts; first, because the covings being parallel to each other, are ill contrived to throw out into the room the heat they receive from the fire in the form of rays; and, secondly, the large open corners occasion eddies of wind which frequently disturb the fire and embarrass the smoke in its ascent, in such a manner as to bring it into the room. Both these defects may be entirely remedied, by diminishing the width of the back of the fire-place. The width which in most cases it will be best to give it, is one-third of the width of the opening of the fire-place in front. But it is not absolutely necessary to conform rigorously to this decision, nor will it always be possible. 

Where a chimney is designed for warming a room of moderate size, the depth of the fire-place being determined by the thickness of the breast to thirteen inches, the same dimensions would be a good size for the width of the back, and three times thirteen inches, or three feet three inches, for the width of the opening in front, and the angles made by the back of the fire-place, and the sides of it, or covings, would be just 135 degrees, which is the best position they can have for throwing heat into the room. In determining the width of this opening in front, the chimney is supposed to be perfectly good, and well situated. If there is any reason to apprehend its ever smoking, it will be necessary to reduce the opening in front, placing the covings at a less angle than 135 degrees, and especially to diminish the height of the opening by lowering the mantle. If from any consideration, such as the wish to accommodate the fire-place to a grate or stove already on hand, it should be wished to make the back wider than the dimension recommended, as for instance, sixteen inches; it will be advisable not to exceed the width of three feet three inches for the opening in front, as in a very wide and shallow fire-place, any sudden motion of the air in front would be apt to bring out puffs of smoke into the room. The throat of the chimney being reduced to four inches, it will be necessary to make a provision for the passage of a chimney sweeper. This is to be done in the following manner. 

In building up the new back of the fire-place, when this wall is brought up so high that there remains no more than about ten or eleven inches between what is then the top of it and the underside of the mantle, an opening or door-way, eleven or twelve inches wide, must be begun in the middle of the back, and continued quite to the top of it, which according to the height that it will commonly be necessary to carry up the back, will make the opening twelve or fourteen inches high, which will be quite sufficient for the purpose. When the fire-place is finished, this door-way is to be closed by a few bricks laid without mortar, or a tile or piece of stone confined in its place by means of a rebate made for that purpose in the brick-work. As often as the chimney is swept, the chimney sweeper removes this temporary wall or stone, which is very easily done, and when he has finished his work, he again puts it in its place. The new back and covings may be built either of brick-work or of stone, and the space between them and the old back and covings, ought to be filled up to give greater solidity to the structure. 

This may be done with loose rubbish or pieces of broken bricks or stones, provided the work be strengthened by a few layers or courses of bricks laid in mortar; but it will be indispensably necessary to finish the work where these new walls end, that is to say, at the top of the throat of the chimney, where it ends abruptly in the open canal or flue, by a horizontal course of bricks well secured with mortar. It is of much importance that they should terminate in this manner; for were they to be sloped outward and raised in such a manner as to swell out the upper extremity of the throat of the chimney in the form of a trumpet, and increase it by degrees to the size of the flue of the chimney, this construction would tend to assist the winds which may attempt to blow down the chimney, in forcing their way through the throat, and throwing the smoke backward into the room. The internal form of the breast of the chimney is also a matter of great importance, and which ought to be particularly attended to. The worst form it can have is that of a vertical plane or upright flat, and next to this the worst form is an inclined plane. 

Both these forms cause the current of warm air from the room which will, in spite of every precaution, sometimes find its way into the chimney, to cross upon the current of smoke which rises from the fire in a manner most likely to embarrass it in its ascent and drive it back. The current of air which, passing under the mantle, gets into the chimney, should be made gradually to bend its course upwards, by which means it will unite quietly with the ascending current of smoke, and will be less likely to check and impede its progress. This is to be effected by rounding off the inside of the breast of the chimney, which may be done by a thick coating of plaster. When the breast or wall of the chimney in front is very thin, it may happen, that the depth of the fire-place determined according to the preceding rules may be too small. Thus supposing the breast to be only four inches thick, which is sometimes the case, particularly in rooms situated near the top of a house, taking four inches for the width of the throat, will give only eight inches for the depth of the fire-place. In this case, it would be proper to increase the depth of the fire-place at the hearth to twelve or thirteen inches, and to build up the back perpendicularly to the height of the top of the grate, and then sloping the back by a gentle inclination forward, bring it to its proper place directly under the back part of the throat of the chimney. This slope, though it ought not to be too abrupt, yet should be quite finished at the height of eight or ten inches above the fire, otherwise it may perhaps cause the chimney to smoke; but when it is very near the fire, its heat will enable the current of rising smoke to overcome the obstacle which this slope will oppose to its ascent, which it could not so easily do, were the slope situated at a greater distance from the burning fuel. There is one important circumstance respecting chimney fire-places designed for burning coals which remains to be examined, and that is the grate. 

Although there are few grates that may not be used in chimneys, altered or constructed on the principles recommended by Count Rumford, yet they are not by any means all equally well adapted for that purpose. Those whose construction is most simple, and which of course are the cheapest, are beyond comparison the best on all accounts. Nothing being wanted but merely a grate to contain the coals, and all additional apparatus being not only useless but pernicious; all complicated and expensive grates should be laid aside, and such as are more simple substituted in their room. The proper width for grates in rooms of a middling size, will be from six to eight inches, and their length may be diminished more or less according to the difficulty of heating the room, or the severity of the weather. But where the width of a grate is not more than five inches, it will be very difficult to prevent the fire from going out. It has been before observed that the use of metals is as much as possible to be avoided in the construction of fire-places, it will therefore be proper always to line the back and sides of a grate with fire stone, which will cause the fire to burn better and give more heat into the room.