Read Ebook: Chimneys & Fireplaces They Contribute to the Health Comfort and Happiness of the Farm Family - How to Build Them by Daniels Ara Marcus

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SMOKE TEST FOR LEAKAGE.

Every flue should be subjected to a smoke test before the heater is connected with it. This may be done as follows: Build a paper, straw, wood, or tar-paper fire at the base of the flue, and when the smoke is passing in a dense column tightly block the outlet at the top by laying a wet blanket over it. If leakage exists at any point, it will immediately become apparent by the appearance of smoke at the opening. Flues so tested frequently reveal very bad leaks into adjoining flues or directly through the walls or between the linings and the wall. When the smoke test indicates leakage, the defect should be remedied before the chimney is accepted for use. Remedying such defects is usually difficult, hence it is wise to watch the construction closely as it progresses. Many brick masons say that all flues leak. This is not true; every flue should be tight.

CLEANING AND REPAIRING THE FLUE.

If a smoke test shows no leakage and the flue is straight, a hand mirror held at the proper angle at the base affords a means of examination for obstructions. Usual causes of stoppage are broken tile leaning inward, mortar accumulations, loose bricks, bird's nests, partly burned paper, soot from soft coal, tarry deposits from burning wood, etc. A weighted bag of hay or straw attached to the end of a rope may be passed up and down the flue to clean it if there is not too great an offset in it.

FIREPLACES.

The use of the fireplace is a very old method of house heating. As ordinarily constructed fireplaces are not efficient and economical. The only warming effect is produced by the heat given off by radiation from the back, sides, and hearth of the fireplace. Practically no heating effect is produced by convection; that is, by air currents. The air passes through the fire, is heated, and passes up the chimney, carrying with it the heat required to raise its temperature from that at which it entered the room and at the same time drawing into the room outside air of a lower temperature. The effect of the cold air thus brought into the room is particularly noticeable in parts of the room farthest from the fire.

The open fireplace, however, has its place as an auxiliary to the heating plant and for the hominess that a burning fire imparts to the room. If one is to be provided, the essentials of construction should be understood and followed so that it will not smoke.

ESSENTIALS OF FIREPLACE CONSTRUCTION.

In order that satisfactory results may be obtained from an open fireplace, it is essential: First, that the flue have the proper area; second, that the throat be correctly proportioned and located; third, that a properly-constructed smoke shelf and chamber be provided; fourth, that the chimney be carried high enough to avoid interference; and fifth, that the shape of the fireplace be such as to direct a maximum amount of radiated heat into the room.

AREA OF THE FLUE.

The sectional area of the flue bears a direct relation to the area of the fireplace opening. The area of lined flues should be a tenth or more of that of the fireplace opening. If the flues are unlined the proportion should be increased slightly because of greater friction. Thirteen square inches of area for the chimney flue to every square foot of fireplace opening is a good rule to follow. For the fireplace shown in figure 13-A, the opening of which has an area of 8.25 square feet, there is required a flue having an area of 107 square inches. If this flue were built of brick and unlined it would probably be made 8 inches by 16 inches, or 128 square inches, because brickwork can be laid to better advantage when the dimensions of the flue are multiples of 4 inches. If the flue is lined the lining should have an inside area approximating 107 square inches. It is seldom possible to secure lining having the exact required area, but the clear area should never be less than that prescribed above.

Failure to provide a chimney flue of sufficient sectional area is in many instances the cause of an unsatisfactory fireplace. The cross section should be the same throughout the entire length of the chimney. Do not contract the flue at the chimney top, for that would nullify the larger opening below; if it is necessary to change the direction of a flue the full area should be preserved through all turns and bends, and the change should be made as gradual as possible.

THE THROAT.

In figure 13-B is shown the throat, the narrow opening between the fireplace and the smoke chamber. Correct throat construction contributes more to efficiency than any other feature except proper flue design. A flue twice as large as is necessary brought straight down to the fireplace without constriction at the throat would result in a poor draft, for the draft does not depend upon the largeness of the flue but upon its proper proportioning to the fireplace and throat. The arrows indicate the upward flowing currents of warm air which are thrown forward at the throat and pass through the smoke chamber into the flue on the inner side. This rapid upward passage of air causes a down current on the opposite side, as indicated by the descending arrows. The down current is not nearly as strong as the up current, but it may be of such force that if there be no throat to the fireplace to increase the velocity of the upward current by constricting it, the meeting of the two currents will result in smoke being forced out into the room. Thus it frequently happens that a fireplace has an ample flue area and yet smokes badly. The influence of the throat upon the upward and downward air currents is shown in figure 13-B.

The area of the throat should not be less than that of the flue. Its length should always be equal to the width of the fireplace opening. The sides of the fireplace should be vertical until the throat is passed. Above the throat the sides should be drawn in until the desired flue area is attained. The throat should be set 8 inches above the location of the lintel, as shown in figure 13, A and B. The wrong way to place the throat damper is shown in figure 15. The throat should not be more than 4 or 5 inches wide. The lesser width is a safe standard. If a damper is installed the width of the brick opening at the throat will depend upon the width of the frame of the damper, the width of the throat proper being regulated by the hinged cover of the damper. If the throat damper is omitted the opening should be 4 inches, as shown in figure 16. The smoke shelf should not be bricked up but should conform to the dotted lines. The depth of the smoke shelf should be the same for a 2-foot as for a 10-foot fireplace opening.

Proper throat construction is so necessary to a successful fireplace that the work should be carefully watched to see that the width is not made more than 4 inches and that the side walls are carried up perpendicularly until the throat is passed, so that the full length of opening is provided. All masons do not appreciate these fine but necessary points. Many prefer their own and sometimes will ignore the proper methods. It is therefore advisable to inspect the work several times a day as it progresses and thus avoid poor results. When trouble is experienced in an existing fireplace that has ample flue area, it is usually found that the formation of the throat is the cause.

SMOKE SHELF AND CHAMBER.

A smoke shelf and chamber are absolutely essential. The shelf is formed by setting the brickwork back at the top of the throat to the line of the flue wall. The shelf should be the full length of the throat. The depth of the shelf should be not less than 4 inches. It may vary from this to 12 or more, depending upon the depth of the fireplace.

The purpose of the smoke shelf is to change the direction of the down draft so that the hot gases at the throat will strike it approximately at a right angle instead of head on. Therefore the shelf should not be bricked up as shown in figures 15 and 16, but should be made as wide as the construction will permit at a height of 8 inches above the top of the fireplace opening.

The smoke chamber is the space extending from the top of the throat up to the bottom of the flue proper and between the side walls, which may be drawn in after the top of the throat is passed. The area at the bottom of the chamber is quite large, since its width includes that of the throat added to the depth of the smoke shelf. This space is capable of holding accumulated smoke temporarily in case a gust of wind across the top of the chimney momentarily cuts off the draft. Smoke might be forced into the room if there were no reservoir to hold it. The smoke chamber also lessens the force of the down draft by increasing the area through which it passes. If the walls are drawn inward 1 foot for each 18 inches of rise, friction is reduced and interference with the draft lessened. The walls should be smooth inside, for roughness seriously impedes the upward movement of the air currents.

SHAPE OF THE FIREPLACE.

The shape of the fireplace proper should be as indicated in figure 13-A. The back should pitch forward from a point a little less than half way from the hearth to the top of the opening, and the sides should be beveled as indicated. Straight back and sides do not radiate as much heat into the room.

THE THROAT DAMPER.

A properly designed throat damper affords a means of regulating the fire. The damper consists of a cast-iron frame with a lid hinged preferably at the back so that the width of the throat opening may be varied from nothing to 6 inches. There are a number of patterns on the market, some of which are designed to support the masonry over the fireplace opening.

A roaring pine fire requires a full throat opening, but slow-burning hardwood logs require but 1 or 2 inches of opening. Regulating the opening according to the kind of fire prevents waste of heat up the chimney. Closing the opening completely in summer keeps flies, mosquitoes, and other insects from entering the house by way of the chimney.

In houses heated by furnaces or other modern systems fireplaces without throat dampers interfere with even heating, particularly in very cold weather. An open fire must be supplied with air and the larger the fire the greater the quantity required; a fireplace with a width of 5 feet or more may pull air from distant parts of the house. This air that is heated at the expenditure of fuel in the furnace is carried up the chimney and wasted, but with a throat damper open only 1 or 2 inches a slow fire of hardwood can be kept going without smoking the room, thus reducing materially the waste of hot air.

PLACING THE THROAT DAMPER.

The throat damper should be as wide as the fireplace, so the side walls should not be drawn in until after the throat is passed. Smoke dampers with lid hinged at the back will help the smoke shelf to turn the down draft; if the lid is hinged in the center the downward and upward currents are apt to conflict. The placing of the damper varies with the type, but generally the bottom of the frame is built into the brickwork at the level of the top of the fireplace opening, forming the throat and supporting the masonry above it.

SIZE OF FIREPLACE OPENING.

Pleasing proportions in the fireplace opening are desirable. The width should generally be greater than the height, but as 30 inches is about the minimum height consistent with convenience in tending the fire, a narrow opening may be made square. Three feet and a half is a good maximum for height of opening unless the fireplace is over 6 feet wide. The higher the opening the greater the chance of a smoky fireplace.

A fireplace should be in harmony with the rest of the room in proportions and details. This consideration and the kind of fuel to be used largely determine the size of opening.

Generally speaking the day of large farmhouse fireplaces capable of receiving cordwood is past. The tending of fires usually falls to the housewife, and cordwood is a heavier weight than she should handle and can not be stored near at hand. Cordwood cut in two is easily handled; so that a 30-inch width is about the minimum for farmhouses where wood is used for fuel. If coal is burned the opening may be made narrower.

DEPTH OF FIREPLACE OPENING.

Unless a fireplace with a 6-foot opening is made fully 28 inches deep, in order that large logs will lie well inside, the advantage of the wide opening is lost, for the logs will have to be split. A shallow opening throws out more heat than a deep one of the same width, but can take only sticks of smaller diameter; thus it becomes a question of preference between the greater depth which permits of large logs that burn longer and require less frequent replenishing and the shallower which takes lighter sticks and throws more heat.

In small fireplaces a depth of 12 inches will permit good draft if the throat is constructed as explained above, but a minimum depth of 18 inches is advised, to lessen the danger of brands falling out on the floor. Wire guards should be placed in front of all fireplaces. In general, the wider the opening the greater should be the depth.

THE HEARTH.

The hearth should be flush with the floor, for sweepings may then be brushed into the fireplace. An ash dump located in the hearth near the back of the fireplace is convenient for clearing ashes and other refuse from the hearth provided there is space below for an ash pit. The dump consists of a cast-iron metal frame, with pivoted cover, through which the refuse can be brushed into the ash pit below. The ash pit should be of perfectly tight masonry and provided with a tightly fitting cleanout door. If a warm-air flue, as described on page 27, is provided, the ash dump will have to be located near one side of the hearth instead of in the center.

THE JAMBS.

The jambs of the fireplace should be of sufficient width to give stability to the structure both actually and in appearance. For a fireplace opening 3 feet wide or less, 16 inches is generally sufficient; for wider openings similar proportions should be kept. Greater widths may be required to harmonize with the proportions of the rooms, and the above should be taken as a minimum.

FIREPLACE BACK AND SIDES.

The back and sides of the fireplace should be constructed of firebrick only. The bricks should be laid flat with the long sides exposed, for if placed with the face exposed there is danger of their falling out.

SUPPORTING IRONS.

In small fireplaces sagging of the arch over the opening seldom occurs, but in fireplaces over 4 feet wide it is not uncommon. It is due to insufficient support of the masonry. Except in massive construction there generally is not sufficient masonry at the sides of the opening to resist the thrust of arch construction; hence it is usual to support the masonry with iron, which, if too light, will sag. Too small an iron will become so hot that its tensile strength is lowered until it bends. A heavy flat bar at least one-half inch thick is sometimes used or a T-bar which has greater strength, but less metal; the wider the opening the heavier the bar required.

IMPROVING FIREPLACE HEATING.

A number of patents have been obtained for improvements in fireplace heating. Most of them, depending on the fact that hot air rises, deliver air heated in or around the fireplace through a register, located above the fire, into the upper part of the room, which is always the warmest part. Furthermore, they require a specially built chimney, precluding the installation of such a device in an existing fireplace. Unless fresh outside air is supplied there is no improvement in the warming of the room.

Patent No. 1251916, issued to Joseph Parsons, of Lakeville, Conn., and by him assigned to the United States Government, presents means of greatly increasing the efficiency of fireplace heating. The inventor's claim differs from other claims for improving fireplace heating in that the operation of his device depends upon the suction created in the chimney by the hot air rising from the fireplace and therefore makes possible the delivery of heated air through a register located at any place in the room or at the hearth. Furthermore, it permits of installation of one of the simpler types in an existing chimney.

For a fire to burn it must be supplied with oxygen. If a fire were built in a fireplace in an air-tight room it would go out as soon as the oxygen present had been consumed unless a down draft in the chimney supplied the needed air. As our fireplace fires do not go out so long as they are fed with fuel it is obvious that the required air supply is obtained from somewhere. Any one who has depended upon a fireplace to heat a room knows that the part of the room farthest from the fire is the coldest and that the temperature around the windows is especially low. In fact the harder the fire burns the colder it is at the windows. The fire must have air, and as cracks exist around windows and doors the air enters through them. The volume entering is equal to that passing up the chimney. This air comes from outside at a low temperature. Figure 18 illustrates how a fireplace fire supplies its needs. When it grows colder outside a bigger fire is made. The bigger the blaze the greater the quantity of outside air drawn into the room through every crack and crevice until, when the outside temperature gets below the freezing point, there is no comfort in the room beyond the immediate vicinity of the fire.

If a room were so tight that the air leakage were insufficient to supply a fireplace fire, it would not burn properly and would smoke. If a pane of glass were removed from a window cold air would rush in through the opening. If the glass were replaced and an opening of equal area be made through the chimney, as shown in figures 19, A and B, so that air could be admitted into the room as indicated by the arrows in the plan, figure 19-B, an equal volume of cold air would be drawn through this opening. As it comes into contact with the metal form the air becomes heated, so that when delivered into the room its temperature would be 100 degrees or higher, depending upon the radiating surface of the hearth, assuming an outside temperature of 32 degrees. If the chimney opening be closed and the pane of glass be again removed the temperature of the air entering through the window would be 32 degrees. It is obvious that the room will be more effectually heated when the air required for combustion is supplied at a high temperature than when supplied through cracks and crevices at a low temperature. All our homes should be made fairly tight for greater comfort in winter. In such a house, with doors and windows closed, the suction caused by the fire can thus be utilized to draw into the room outside air heated in passing through a metal flue on which the fire is burning.

The principle may be applied in various forms. Figure 19-A illustrates a simple form for use in connection with an outside chimney. A piece of galvanized sheet iron is bent to the proper form and set into the fireplace so as to leave an air space between it and the back and sides of the fireplace. An opening to the outside is made by removing two or three courses of brick. Air enters through this, becomes heated by contact with the metal, and is delivered into the room at the sides of the fireplace, as indicated in the plan of figure 19-B. It immediately rises within the room, gives up part of its heat, and eventually whirls about and into the fire, as indicated by the arrows in figure 19-A. This form would not necessarily heat the entire room effectually; it would, however, supply heated air for the fire in volume sufficient to replace or materially reduce the quantity of cold air which would otherwise enter through window and door cracks. With a brisk fire burning, a rush of warm air can be felt 6 or 8 feet away from the fireplace.

This simple form may be built as follows: A piece of roofing tin about 6 inches wider than the height of the fireplace opening, with length equal to the width of the opening plus twice the depth of the side, should be secured. It should then be marked and cut as indicated in the form , and bent into a shape similar to that shown in the perspective, same figure. When placing it, there should be a space left between the tin and the brickwork at both back and top. The back and sides at the top should be bent back 2 inches to meet the brickwork. The crack or joint should be tightly closed with asbestos or furnace cement. The tin form rests on the 4-inch bottom flange. The joint here can be made tight by placing a few brick on the flange and covering with ashes, or a metal plate cut to the proper shape may be laid upon and preferably riveted to the lower flanges of the back and sides. The form should be as high as the opening and the metal sides should project about 3 inches beyond the jambs, so as to throw the heated air well out into the room. A one-fourth-inch rod placed across the top of the tin form directly under the arch iron of the fireplace assists in holding the top of the tin firmly against the brickwork.

Figure 20 shows a simple form for use with an inside chimney. A hole may be cut in the hearth on one side and connected with the outside by means of a passage through the chimney foundation. The manner of providing this passage will depend upon the construction in the particular case. A galvanized sheet-metal box with a division plate extending part way through it is set on the hearth. The side over the opening is bent down in front, as at A, so that the entering cold air must pass to the rear around the division plate and then out into the room in front of the hearth, as at B. The fire, on top of the metal flue, heats the air issuing at B as it flows under it. Figure 21 shows an improved form in which the flue and division plate are extended up the back of the fireplace. This presents considerably more radiating surface, so that the air can be heated to a higher temperature. The air issuing from this flue at B is discharged farther out into the room. If there is a cellar under the floor a metal duct must be employed to bring fresh air from an opening in the outside wall, just below the joists, to the hole in the hearth. Cellar air should never be sucked through the flue. All openings under the house or through the wall should be screened to keep out rats and mice, and doors should be provided to close the openings entirely if desired.

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