T. A. H. Miller

“ It is more likely to form when wood is used for fuel than when coal is burned and is more likely to form in cold than in mild climates. Green wood may contain as high as 40 percent water, and dry wood 15 to 20 percent. When wood is slowly burned, it gives off acetic and pyroligneous acid, which in combination with water or moisture form creosote. When the draft is strong and an active fire is maintained, much of the creosote is carried off into the atmosphere. The trouble is aggravated when the fire does not burn briskly and when an outside flue is subjected to chilling blasts. ”

“ In houses heated by furnaces or other modern systems, lack of a damper in the fireplace flue may interfere with uniform heating, particularly in very cold windy weather, whether or not there is a fire on the hearth. When air heated by the furnace is carried up the chimney there is a waste of the furnace fuel, but a damper partially open serves a slow fire of hardwood without smoking the room or wasting heated air from the main heating system. ”

“ When a fireplace smokes, it should be examined to make certain that the essential requirements of construction as outlined in this bulletin have been fulfilled. If the chimney is not stopped up with fallen brick and the mortar joints are not loose, note whether nearby trees or tall structures cause eddies down the flue. To determine whether the fireplace opening is in correct proportion to the flue area, hold a piece of sheet metal across the top of the fireplace opening and then gradually lower it, making the opening smaller until smoke does not come into the room. ”

“ Trouble with creosote and soot can be reduced when one understands how they are formed. Smoke and soot are caused by imperfect combustion, usually due to one or all of the following conditions: (1) Lack of sufficient air to the fire; (2) improper mixture of air with furnace gases; (3) low furnace temperature; (4) too small combustion space so that the gases reach the comparatively cool furnace surface before they are completely burned and, as a result, soot or tarry matter condenses and then passes up the chimney in the form of smoke. Soft coal causes more soot trouble than hard coal. ”

“ Where suitable stone is difficult to get in sufficient quantity, the exposed surface may consist of a shell the thickness of the stone and the inner portion of the wall be made of concrete or large stone bedded in concrete. When flue lining is necessary, it will serve as a form for the flue: otherwise a metal stovepipe makes a practical form, or the flue can be formed of brick laid on edge. The stones can be laid and the concrete deposited with the least trouble by building the veneer and flue only 6 to 8 inches high at one time. All masonry should be laid in mortar, as described on page 10. ”

“ If the flashing is sound, possibly water runs down the inside of the flue and through defective mortar joints. Where these cannot be reached readily, the chimney may have to be torn down and rebuilt. Sometimes a hood (fig. 18, A and B) is built on top of the chimney to keep out water or to prevent wind blowing down it. To prevent dampness being drawn up from the ground, the mortar can be raked from a joint at least 12 inches above the ground and a layer of slate, asbestos shingles, or rust-resistant sheet metal and new mortar worked into the joint. ”

“ A very common error in chimney design is failure to distinguish between the size of the flue required for free passage of the volume of smoke from a given amount of fuel and that which, with proper height, will produce the required draft. ”

“ When the wood is nearly charred, most of the smoke has been driven off and the chimney is hot enough to draw the smoke up the flue. All fires should be banked before they are left, to avoid setting fires. Banking can be safely and effectively done by raking the coals and unconsumed fuel into a pile on the hearth and covering the pile with a few inches of earth. Water thrown on a hot fire may result in scalds from the steam and may crack the fireplace. ”

“ No wood should be in contact with a chimney. Leave a space of 2 inches between the outside face of a chimney and all wooden beams or joists except when 8 inches of masonry is used outside flue lining, in which case the framing may be within one-half inch of the chimney masonry. The space between the floor framing and the chimney may be filled with porous, nonmetallic, incombustible material, such as loose cinders. Brickwork, mortar, and concrete are not suitable. ”

“ If the oven is intended for baking, it is advisable to line it with firebrick, and the masonry should be at least 8 inches thick. A greater heat-storing capacity is secured by using thick walls. An ash drop of standard cast-iron unit type is provided for modern ovens and may lead either to the side of the fireplace or to an ash-pit in the chimney base. The throat or dome should be carefully formed with brick molded or ground to an arch and preferably should be fitted with a damper. If the top of the oven is flat, several lintel irons will be needed to support the brick. ”

“ Frequently metal-pipe extensions are provided to increase the height of a flue on account of the low cost and ease of installation, but these must be securely anchored against wind and have the same area as the flue. Metal extensions are likely to rust in a short time. They are available with a metal cowl or top that turns with the wind to prevent air blowing down the flue. Terra-cotta chimney pots or extensions are more durable and attractive.
A chimney located entirely inside a building has better draft because the masonry retains heat longer when protected from cold outside air. ”

“ If a damper is installed, the width of the opening j, figure 34, will depend on the width of the damper frame, the size of which is fixed by the width and depth of the fireplace and the slope of the back wall. The width of the throat proper is determined by the opening of the hinged damper cover. The full damper opening should never be less than the flue area. Responsible manufacturers of fireplace equipment give valuable assistance in the selection of a suitable damper for a given fireplace. A well-designed and well-installed damper should be regarded as essential in cold climates. ”

“ Likelihood of success in cleaning is greater when the deposits of soot are thick, provided they do not cut down the draft too much. If burning is employed, there is less risk when it is done frequently enough to prevent large accumulations, which cause intense fires. Also, freeing the heater and pipe of soot permits better fuel burning and higher temperatures in the chimney flue, thus reducing the amount of soot likely to be deposited on the flue walls. ”

“ No range, stove, fireplace, or ventilating register should be connected with the flue being used for the heating apparatus because this is a frequent cause of unsatisfactory operation. Fires may occur from sparks passing into one flue opening and out through another where there are two connections to the same flue. If an abandoned fireplace chimney is to be used for a range or stove, close the fireplace flue tight about a foot below the smoke pipe hole. ”

“ Chimneys extending above the roof are exposed to the wind and may sway enough during a gale to open up the mortar joints at the roof line. Openings in a flue at this point are especially dangerous because sparks from the flue may come in contact with the woodwork of the roof. It is therefore good practice to make the upper walls 8 inches thick (fig. 11) by starting to offset the bricks just below the intersection with the roof.
The brickwork around all fireplaces and flues should be laid with cement mortar, as it is more resistant than lime mortar to the action of heat and flue gases. ”

“ A heavy chain drawn up and down the flue walls is sometimes effective. However, when creosote is removed, care is necessary not to knock out mortar joints or to break the flue lining.
Large quantities of salt thrown on the fire in the grate or fireplace will extinguish a chimney fire. A fire in a fireplace flue can be checked in its intensity and frequently extinguished by first quenching the fire on the hearth and then holding a wet rug or blanket over the opening so as to shut off the air. ”

“ Paving the ground around the fireplace, with flagstones or covering it with a layer of gravel or sand will prevent the area from becoming a mudhole or an unsightly bare spot; also, danger of starting brush fires by sparks falling from the firebox is lessened.
Fireboxes 12 to 16 inches wide, 16 to 24 inches long, and 6 to 8 inches deep with the hearth at 9 to 16 inches above the ground are sufficient for most purposes. Large fireboxes are wasteful of fuel; while, if the grille is too high above the hearth, much of the best cooking heat from glowing coals is lost. ”

“ Tests made by the Bureau of Agricultural Chemistry and Engineering showed that about five times the amount of air required for even liberal ventilation may be drawn into a living room by the operation of a fireplace. ”

“ Deep pockets permit the accumulation of soot, which may take fire; therefore start them from a point preferably not more than 8 inches below the center line of the smoke pipe intake and fill the lower part of the chimney with solid masonry instead of extending the pocket to the base of the chimney as is often done. Clean-out doors are necessary at the bottom of deep pockets and, if used, must fit snugly and be kept tightly closed so that air cannot get in. ”

“ The dimensions of a flue for adequate draft depend principally on the grate area and type of heating plant [1] and on the kind of fuel to be burned, both of which should be determined before construction is begun. If a chimney is found to be inadequate the only method of improving it, short of reconstruction, is to increase its height. ”

“ The walls of the chimney, being comparatively cool, cause condensation of the vapors contained in the smoke. Thus the creosote condenses and runs down the flue, finding its way out of any joints that are not perfectly tight. The formation of creosote is unusual in chimneys that are surrounded by warm rooms. The outer walls of a chimney in an outside wall should be at least two bricks thick and the chimney should have a good flue lining. ”

“ The lower section of flue lining, unless resting on solid masonry at the bottom of the flue, should be supported on at least three sides by brick courses projecting to the inside surface of the lining. When laying brick and lining, it is advisable to draw up a tight-fitting bag of straw as the work progresses so as to catch material that might fall and block the flue. ”

“ Pleasing designs result from exercising good taste in use of materials and mantels that suit the room. The photographs in this bulletin have been selected to illustrate various architectural effects that can be developed and should help in the choice of a type suitable for houses of different designs. The essentials for safety and utility, however, should not be sacrificed for style. ”

“ In mild climates a properly built fireplace will heat a single room, and when equipped with a convection heater will also heat a second room on the same floor or an upper floor. In colder climates it is a useful adjunct to other heating systems if provided with a damper. ”

“ The jambs should be wide enough to give stability and a pleasing appearance; they are frequently faced with ornamental brick or tile. For an opening 3 feet wide or less, a 12- or 16-inch width is generally sufficient, depending on whether a wood mantel is used or the jambs are of exposed masonry. The edges of a wood mantel should be kept at least 8 inches from the fireplace opening. ”

“ If, after a chimney is cleaned, an examination discloses holes, unfilled joints, or other unsound conditions out of reach for repair, it is advisable to tear the masonry down and rebuild properly. Inside bricks that are impregnated with creosote and soot should not be used in the new work because they will stain plaster whenever dampness occurs. It is almost impossible to remove creosote and soot stains on plaster and wallpaper. ”

“ Walls of chimneys not more than 30 feet high when lined should be 4 inches thick if of brick and reinforced concrete, 8 inches if of hollow building units, and 12 inches if of stone. Linings may be omitted in chimneys having walls of reinforced concrete at least 6 inches thick or of unreinforced concrete or brick at least 8 inches thick, although lining is desirable in the case of brick construction. Also the outside wall of a chimney exposed to the weather is best made at least 8 inches thick. ”

“ No one type will meet all conditions, but all types should be practical to use and yet not be fire hazards or eyesores.
Figure 40.—A, A fireplace built for 30 cents, cash. One hundred and twenty bricks and six concrete blocks were picked up a few at a time along the road. One sack of cement was purchased, one-half of which was used for another job Sand was available on the site. B f Detailed drawings show dimensions of this fireplace. As the fireplace is ordinarily built, the material would cost about $5 and the labor from $5 to $10, depending on local conditions. ”

“ A metal casing or asbestos board 2 inches from the upper half of the pipe is sometimes employed to protect woodwork directly above it. A pipe, even so protected, should never be closer than 9 inches to any woodwork or other combustible material. ”