The Useful Arts Employed in the Construction of Dwelling Houses. Second Edition

by Anonymous

Remedies for some of these Defects.

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 by Dr. 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 which Dr. 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 to be 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 of which, 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 a register stove is 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 air from 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 the room, 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 by Dr. 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 made no 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 in Dr. 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 of close stoves, intended to obviate the ill effects attendant on open fire-places. These must be briefly noticed.