This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The subject of smoky chimneys is undoubtedly most important and most difficult. In Chapter VI (Broad Irrigation)., Section II., Vol. I., certain rules were laid down for the construction of fireplaces, flues, and chimney-stacks, and a perusal of these will, it is hoped, be of some service in connection with the cure of smoky chimneys, although they do not cover the whole ground. The defects of existing chimneys may be defects of construction (including form, size, and workmanship) or of position (including fireplace, flue, and stack).
Defects of construction, if due to bad workmanship, may not be very serious; perhaps a few bricks or some large droppings of mortar have partially blocked the flue. These can be discovered by the sweeper, and can usually be removed by dragging a suitable "core" down the flue; if not, their position can he approximately ascertained, and they can be removed after ratting out the brickwork in front.
If the Hue is in any part too nearly horizontal, it can only be remedied at considerable inconvenience and expense. One case of this kind was altered by the writer, as shown in Fig. 686, with very satisfactory results, new windows being at the same time inserted in order to light and ventilate the attics. The defect, however, cannot always be so easily removed.
The size of the flue is often a serious fault. In old houses especially, the flues are usually much too large, having been built in the days when boys climbed the flues in order to sweep them. As a rule, such chimneys smoke when the tires are first lighted, but cease to smoke when the whole of the flue is thoroughly wanned. A good plan is to burn some shavings for a short time before laying the coals. The lessening of a flue is not an easy matter. The lowest part (which is often the worst) can be bricked up to a considerable height, after removing the range; perhaps the best method of completing the reduction is to cut holes into the flue at intervals, and place 9-inch drain-pipes or flue-pipes within the old flue.
The construction of the chimney-stack is often defective. If the brickwork of the stack is thin and porous, it may become soaked with rain, and thus chill the air in the flue and so reduce the draught Pointing the joints, or covering the stack with stucco, may do some good, but reconstruction in a more substantial way and with better materials is the most thorough remedy; a damp course of lead or ether material, inserted immediately above the roof, will prevent moisture soaking into the rooms below. The "mid-feathers", or brickwork between the several flues, sometimes give way, and thus help to choke the flues, while at the same time the smoke from one flue may be drawn down another flue into the house. The cure of this defect is obvious.
The lack of air-inlets in the room is often the cause of unsatisfactory draught in the flue. In his Report on "Sanitary Works at Windsor Castle, 1863 Sir (then Mr.) Robert Rawlinson wrote: "To prevent smoky chimneys, about seventy of the most troublesome rooms have been ventilated and otherwise improved". Another extract from the same report gives an example of improving large flues in the way indicated in the last paragraph but one: " In the numerous structural alterations made in Windsor Castle, the old large and open chimney-spaces of mediaeval periods have been made good. All new chimney-flues are lined with fire-clay tubes, flushed and grouted-in solid."
Fig 686 - Alteration of Chimney stacks in consequence of insufficient Inclination of Flues.
The position of the fireplace cannot usually be altered without very great expense. It may, however, be pointed out that fireplaces against external walls often smoke on account of the flue being chilled. Any external protection, such as weather-tiling, will be of service in cases of this kind.
The position and height of the chimney-stack are very frequent causes of smoky fireplaces. Chimney-stacks rising from the eaves of a roof are great sinners, and sometimes the defect can only be cured by raising the stack a little higher than the ridge of the roof, and crowning it with a suitable cowl. Chimney-teles on gables are also liable to blow-downs, when the wind is in the direction of the ridge. The neighbourhood of loftier buildings, trees, rocks, etc, causes smokiness in chimneys, in consequence of gusts of wind blowing over the loftier objects and sweeping down upon the flues. The houses in mountainous districts furnish lessons for us in cases like these. In the Pyrenees and the middle of Cor-i. as well as in the Alps and the mountainous parts of our own country, I have been struck with the diminutive chimney-stacks, which the builders have deemed sufficient. Many of them, even when placed near the eaves, do not rise more than a foot or two above the roof, but almost invariably the top of the flue is covered, and the smoke escapes through openings in the sides of the stack. Sometimes the covering is a flag supported on a stone at each corner, and perhaps weighted with a large stone to prevent it being blown off. Sometimes the cover is formed with two flags or slates, sloping to a ridge over the flue. The important feature of all is that a direct blow-down is impossible, and my experience is that chimney-cowls with side openings and with the top covered are more frequently successful in preventing blow-downs than any other kind.
The Pembridge chimney-cowl, illustrated in Fig. 687, is a simple example of this kind. I have tried it on a troublesome flue, on two sides of which are loftier buildings, and it has proved quits satisfactory; it has, however, the disadvantage of great breadth, and cannot be used for a series of flues of ordinary size. It is also somewhat difficult to sweep, as the top is fixed.
Fig. 687. - Elevation and faction of the Pembridge Chimney-cowl.
Green's patent chimney-pot is an ingenious contrivance. As shown in Fig. 688, it can be obtained either with or without the covering at the top. The makers recommend that the pot alone should first be fixed, " as this usually effects a cure, but if this is not entirely successful, then the cowl, which is of cast-iron and drops in at the top of the pot, may be added". On removing the cast-iron "cowl", the flue and pot can be easily swept.
Fig. 688. - Green's Patent Chimney-pot A, without cowl; b, with cut-iron cowl.
Fig 689. - Elevation. Section, and Plan of the " Success " Chimney-pot.
This pot and cowl together will undoubtedly prevent a blow-down in nearly every case.
Cowls with fast tops, such as the Pembridge cowl, interfere somewhat with the sweeping of the flue, and attempts have therefore been made, as in the "Success" chimney-pot, to prevent blow-downs by providing outlets in the sides of the pot, while leaving the top uncovered. The arrangement is not always satisfactory.
The three cowls illustrated in figs. 687, 688, and 689, have the great advantage of being made of fire-clay or glazed earthenware, these materials being practically indestructible by ordinary agencies.
382 the improvement of existing houses.
Cowls of sheet-iron or steel soon corrode, and should only be used when earthenware or fire-clay cowls have failed to effect a cure. Fig. 690 shows a common form. 1 have found Boyle's cowl (Fig. 691) successful, but it will only last a few The "lobster-back" cowl and the rotary cowl are also used, but it is best to avoid appliances with movable parts wherever possible, as they require regular attention, and are not very durable; moreover, some of them are very noisy. A somewhat curious metal cowl, without movable parts, is shown in fig 692; it is known as Cooper's patent "Acme". and is said to have proved satisfactory in many cases.
Fig. 690. - Chimney cowl of Sheet Iron or Steel.
Fig. 691. - Boyle's Chimney-cowl.
Fig. 692 - Cooper's "Acme" chimney cowl.
A. for fitting on existing chimney - pots; B, with square base and flange.