Fig. 13.—A. Top of throat damper is at DD, smoke shelf at CO. Side wall should not be drawn in until the height DD is passed. This assures full area. If the drawing in is done as indicated by lines EF and EG, the width of the throat becomes less than the width of the opening and causes the air currents to pile up in the corners of the throat, resulting frequently in a smoky fireplace. B. Correct fireplace construction.
Fig. 13.—A. Top of throat damper is at DD, smoke shelf at CO. Side wall should not be drawn in until the height DD is passed. This assures full area. If the drawing in is done as indicated by lines EF and EG, the width of the throat becomes less than the width of the opening and causes the air currents to pile up in the corners of the throat, resulting frequently in a smoky fireplace. B. Correct fireplace construction.
Fig. 13.—A. Top of throat damper is at DD, smoke shelf at CO. Side wall should not be drawn in until the height DD is passed. This assures full area. If the drawing in is done as indicated by lines EF and EG, the width of the throat becomes less than the width of the opening and causes the air currents to pile up in the corners of the throat, resulting frequently in a smoky fireplace. B. Correct fireplace construction.
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.
Fig. 14.—Fireplaces constructed like this without throat will very likely smoke.
Fig. 14.—Fireplaces constructed like this without throat will very likely smoke.
Fig. 14.—Fireplaces constructed like this without throat will very likely smoke.
Infigure 13-Bis 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 (seefig. 14) 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 infigure 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. (Seefig. 13-A.) The sides of the fireplace should be vertical until the throat is passed. (DD infig. 13-A.) 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 infigure 13, A and B. The wrong way to place the throat damper is shown infigure 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 infigure 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.
Fig. 15.—Wrong location for throat damper. The throat is so low that the accumulation of gases at the point constricted weakens rather than improves the draft with greater likelihood of a smoky fireplace. Note that the smoke shelf is bricked up. This is wrong.
Fig. 15.—Wrong location for throat damper. The throat is so low that the accumulation of gases at the point constricted weakens rather than improves the draft with greater likelihood of a smoky fireplace. Note that the smoke shelf is bricked up. This is wrong.
Fig. 15.—Wrong location for throat damper. The throat is so low that the accumulation of gases at the point constricted weakens rather than improves the draft with greater likelihood of a smoky fireplace. Note that the smoke shelf is bricked up. This is wrong.
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 figures15and16, 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. Thearea 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 infigure 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.
Fig. 16.—This construction without a throat damper directs the down draft so that it meets the up draft almost at the throat, which is more faulty than the construction shown infig. 15, for there the lid of the damper deflects the down current.
Fig. 16.—This construction without a throat damper directs the down draft so that it meets the up draft almost at the throat, which is more faulty than the construction shown infig. 15, for there the lid of the damper deflects the down current.
Fig. 16.—This construction without a throat damper directs the down draft so that it meets the up draft almost at the throat, which is more faulty than the construction shown infig. 15, for there the lid of the damper deflects the down current.
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 thehouse. 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.
Fig. 17.—Smoke dampers with lids hinged in the center do not turn the up draft as well as do those hinged at the rear side.
Fig. 17.—Smoke dampers with lids hinged in the center do not turn the up draft as well as do those hinged at the rear side.
Fig. 17.—Smoke dampers with lids hinged in the center do not turn the up draft as well as do those hinged at the rear side.
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 ofthe 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 supportthe 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 18illustrates 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.
Fig. 18.—All air required for feeding the fire must pass through the room, entering through cracks around windows and doors and producing an uncomfortable temperature in all parts of the room except near the hearth.
Fig. 18.—All air required for feeding the fire must pass through the room, entering through cracks around windows and doors and producing an uncomfortable temperature in all parts of the room except near the hearth.
Fig. 18.—All air required for feeding the fire must pass through the room, entering through cracks around windows and doors and producing an uncomfortable temperature in all parts of the room except near the hearth.
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 infigures 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. (Tests by the writer have shown this temperature to be higher than 125 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.
PERSPECTIVE
The principle may be applied in various forms.Figure 19-Aillustrates 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 offigure 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.
Fig. 19.—Simple form of warm-air flue for outside chimney. Air required for feeding the fire is brought in from the outside around a metal form set in the fireplace, with a space between it and the back and sides of the brickwork. As the cold outside air passes around the metal it becomes heated and is delivered into the room at a temperature much higher than where it is pulled in through window and door cracks. The result is a much more comfortable room.
Fig. 19.—Simple form of warm-air flue for outside chimney. Air required for feeding the fire is brought in from the outside around a metal form set in the fireplace, with a space between it and the back and sides of the brickwork. As the cold outside air passes around the metal it becomes heated and is delivered into the room at a temperature much higher than where it is pulled in through window and door cracks. The result is a much more comfortable room.
Fig. 19.—Simple form of warm-air flue for outside chimney. Air required for feeding the fire is brought in from the outside around a metal form set in the fireplace, with a space between it and the back and sides of the brickwork. As the cold outside air passes around the metal it becomes heated and is delivered into the room at a temperature much higher than where it is pulled in through window and door cracks. The result is a much more comfortable room.
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 (fig. 19-B), 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.
Fig. 20.—Simple form of warm-air flue for inside chimney.
Fig. 20.—Simple form of warm-air flue for inside chimney.
Fig. 21.—Improved form of warm-air flue for Inside chimney. The increased radiating surface obtained by conducting the metal flue up the back of the fireplace heats the air to a higher temperature so that it is delivered into the room farther from the outlet duct.
Fig. 21.—Improved form of warm-air flue for Inside chimney. The increased radiating surface obtained by conducting the metal flue up the back of the fireplace heats the air to a higher temperature so that it is delivered into the room farther from the outlet duct.
Fig. 21.—Improved form of warm-air flue for Inside chimney. The increased radiating surface obtained by conducting the metal flue up the back of the fireplace heats the air to a higher temperature so that it is delivered into the room farther from the outlet duct.
Figure 20shows 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 21shows 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 mustbe 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.
Fig. 22.—Improved form of warm-air flue with floor register. This method increases the efficiency of fireplaces many times by delivering the air that must be supplied to the fire into the room at temperatures of 100° and higher, depending upon the form and extent of the heating surface at the back of the fireplace, and delivering it to the coldest part of the room so that heat is distributed more effectively and the entrance of cold air around windows and doors is reduced to a minimum.
Fig. 22.—Improved form of warm-air flue with floor register. This method increases the efficiency of fireplaces many times by delivering the air that must be supplied to the fire into the room at temperatures of 100° and higher, depending upon the form and extent of the heating surface at the back of the fireplace, and delivering it to the coldest part of the room so that heat is distributed more effectively and the entrance of cold air around windows and doors is reduced to a minimum.
Fig. 22.—Improved form of warm-air flue with floor register. This method increases the efficiency of fireplaces many times by delivering the air that must be supplied to the fire into the room at temperatures of 100° and higher, depending upon the form and extent of the heating surface at the back of the fireplace, and delivering it to the coldest part of the room so that heat is distributed more effectively and the entrance of cold air around windows and doors is reduced to a minimum.
Figure 22shows a more elaborate installation. This insures very satisfactory heating with a fireplace fire. The piece A B C D of galvanized metal has a rectangular cross section. Two or three courses of brickwork are omitted and the metal duct is set into the fireplace, so that radiation from the fire impinges upon its surface from B to D. The air entering from outside at AE is heated as it passes through the flue behind and under the fire and is carried through another rectangular duct under the floor to a register located in a far part of the room. Out of this register air in large volume is discharged at a high temperature. This air heats the far part of the room and other parts as it travels from the register upward and through the room to the fireplace. Thus the fireplace heats the room by convection of heat as well as by radiation, and all parts of the room are more comfortable than if radiation alone were depended upon. A test of an installation similar to that shown infigure 22was made by the writer. The fireplace and suction fluewere built in a cabin measuring 24 feet square by 9 feet high. The test was conducted late in November on a night when the outside temperature was 24° F. It was the first fire built in the fireplace in that season, consequently all the materials of the building were cold. The room was practically air-tight; very little leakage could be felt around the windows. A temperature of slightly over 100° was recorded directly over the register, in the center of the room it was 72°, and in the farthest corner a thermometer, hung about 18 inches from the wall between two windows, showed 65°.
Thus the efficiency of fireplaces may be materially increased, the degree depending upon the character of the air duct installed. Even in the simple types the air required to make the fire burn enters the room at a higher temperature at the floor instead of around windows and doors at a low temperature; windows and doors may therefore be made tight, so as to reduce the cold-air leakage. The type with a register in the far part of the room supplies heat to parts of the room or to an adjoining room, which would receive little heat if radiation only were relied upon. This means of improving fireplace heating is particularly adapted to small houses in the South, where the open fire is the most common method of house heating. As the simple types require only galvanized Sheet metal bent at right angles, it is within the means and ability of many to supply themselves with flues of their own making.
WASHINGTON: GOVERNMENT PRINTING OFFICE: 1921
Transcriber NoteIllustrations were moved so as not to split paragraphs. Hyphenization has been standardized to the most common form.
Transcriber Note
Illustrations were moved so as not to split paragraphs. Hyphenization has been standardized to the most common form.