Fireplaces and Chimneys

Footings

Footings for chimneys with fireplaces should be provided as described on page 7; for chimneys without fireplaces, the footings should rest on good firm soil.

The hearth should be about flush with the floor, for sweepings may then be brushed into the fireplace. When there is a basement, an ash dump located in the hearth near the back of the fireplace is convenient. The dump consists of a metal frame about 5 by 8 inches in size, with a plate, generally pivoted, through which ashes can be dropped into a pit below (fig. 35).

In buildings with wooden floors the hearth in front of the fireplace should be supported by masonry trimmer arches (fig. 34) or other fire-resistant construction. Hearths should project at least 16 inches from the chimney breast and should be of brick, stone, terra cotta, or reinforced concrete not less than 4 inches thick. The length of the hearth should be not less than the width of the fireplace opening plus 16 inches. Wooden centering under trimmer arches may be removed after the mortar has set, though it is more frequently left in place. Figure 36 shows a recommended method of floor framing around a fireplace.

Wall Thickness

The walls of fireplaces should never be less than 8 inches thick, and if of stone they should be at least 12 inches thick. When built of stone or hard-burned brick, the back and sides are often not lined with firebrick, but it is better to use firebrick laid in fire-clay. When firebricks are laid fiat with the long sides exposed there is less danger of their falling out. They are generally placed on edge, however, forming a 2-inch protection, in which case metal ties should be built into the main brickwork to hold the 2-inch firebrick veneer in place. Thick metal backs and sides are sometimes used as lining. When a grate for burning coal or coke is built in, firebrick at least 2 inches thick should be added to the fireplace back unless the grate has a solid iron back and is only set in with an air space behind it (fig. 37).

Jambs

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. For wider openings and large rooms, similar proportions should be kept.

Where a masonry arch (fig. 38) is used over the opening, the jambs should be heavy enough to resist the thrust of the arch. Arches over openings less than 4 feet wide seldom sag, but sagging is not uncommon in wider fireplaces, especially where massive masonry is used.

Throat

The sides of the fireplace should be vertical up to the throat, or damper opening (ff fig. 34). The throat should be 6 to 8 inches or more above the bottom of the lintel and have an area not less than that of the flue and a length equal to the width of the fireplace opening. Starting 5 inches above the throat, ee, the sides should be drawn in at tt to equal the flue area.

Proper throat construction is so necessary to a successful fireplace that the work should be inspected several times a day during construction to make certain that the side walls are carried up perpendicularly until the throat is passed and that the full length of opening is provided.

Smoke Shelf and Chamber

The smoke shelf is made by setting the brickwork back at the top of the throat to the line of the flue wall for the full length of the throat. Its depth may vary from 6 to 12 inches or more, depending on the depth, d, of the fireplace.

Damper

A properly designed damper, as shown in figure 34, affords a means of regulating the draft and prevents excessive loss of heat from the room when the fire is out. A damper consists of a cast-iron frame with a lid hinged so that the width of the throat opening may be varied from a closed to a wide-open position. Various patterns are on the market, some designed to support the masonry over the opening, others requiring lintel irons.

Flue

The area of lined flues should be a twelfth or more of the fireplace opening, provided the chimney is at least 22 feet in height, measured from the hearth. If the flue is shorter than 22 feet or if it is unlined, its area should be made a tenth or more of the fireplace opening. The fireplace shown in figure 34 has an opening of 7.5 square feet, or approximately 1,080 square inches, and needs a flue area of approximately 90 square inches; a rectangular flue, 8% by 18 inches, outside dimensions, or a round flue with a 12-inch inside diameter might be used, as these are the nearest commercial sizes of lining (table 2). It is seldom possible to obtain lining having exactly the required area, but the inside area should never be less than that prescribed above. A 13- by 13-inch flue was selected for convenience when combining with the other flues. If the flue is built of brick and is unlined, its area should be approximately one-tenth of the fireplace opening, or 108 square inches. It would probably be made 8 by 16 inches (128 square inches) because brickwork can be laid to better advantage when the dimensions of the flue are multiples of 4 inches. The principles of construction given under Chimneys (p. 7) apply to fireplace flues.

Table 4 is convenient in selecting the proper size of flue or for determining the size of fireplace opening for an existing flue. The area of the fireplace opening in square inches is obtained by multiplying the width, w, by the height, h, (fig. 34), both measured in inches.

COST ESTIMATE

A convenient method for estimating the number of bricks in a chimney is to calculate the volume of the various sections which differ in outside dimensions and then subtract the voids or cavities resulting from ash-pits, fireplace, and flues. This will be the total cubic feet of brickwork which, when multiplied by 22.5, is converted to number of bricks. For convenience, inches as indicated in figure 39 have been converted to decimals of a foot. [6]

Table 4.—Sizes of fireplace flue linings[D]

Number of Bricks

(1) Estimate the total volume of masonry by multiplying together the length, width, and height of the various sections (fig. 39).

(2) Estimate the total volume of voids by multiplying together their length, width, and height.

(3) Subtract volume of voids from volume of masonry.

(4) Multiply net volume of masonry by the number of brick per cubic foot.

269 by 22.5 = 6,053 brick, or 6.1 thousand bricks.

Mortar

To estimate the mortar needed, multiply the mortar material given below for 1,000 brick by 6.1 to determine how much will be needed to build the chimney, using 1:1:6 mixture recommended on page 10.

Foundation

Concrete needed for foundation can be estimated as follows: Concrete for foundation should be 1:2½:5 and for the top 1:2½. The foundation is 7 by 3.75 by 1, or 26.25 cubic feet, or 1 cubic yard, and will require 5 sacks of cement, 0.46 cubic yard of sand, and 92 cubic yard of gravel. The cap is 4.5 by 2.66 by 0.5 = 5.9 cubic feet The area of the three flues above must be deducted: 5.9 minus 2.48 = 3.42 cubic feet, or one-ninth of a cubic yard. As 1 cubic yard was assumed for the foundation, extra cement and sand are not needed. Other material needed:

If firebrick is to be used or the exposed breast is to be of face or special brick (or ceramic tile) the number should be counted or estimated and deducted from the number of common brick as estimated above.

Labor

The labor required to build a chimney depends on the thickness of the walls, the height, and the amount of cutting to build in specialties, provide offsets, etc. In general, a mason will take 16 hours with 8 hours of laborer's help to lay 1,000 brick. On this basis, 16 by 6.1 = 97.6 hours of mason's time and 48.8 hours of laborer's time will be required.

Cost

The approximate cost of the chimney can be determined by using actual local cost of materials and wages as follows:[F]

SMOKY FIREPLACES

OUTDOOR FIREPLACES

TYPES

The tendency is to build too large an outdoor fireplace. Where only a little cooking is to be done occasionally in a small yard or at a picnic, several concrete blocks or stones set on the ground about 12 to 16 inches apart will serve. The shelf of an old refrigerator may be used for a grille. If permanence is desired, the walls should be laid in cement mortar and the fireplace should have a suitable foundation and a permanent grille. An end wall is recommended to prevent embers from being scattered by drafts blowing between the side walls. Smoke annoyance while cooking is lessened by making the fireplace long enough to permit a short chimney (fig. 40).

Fireplaces opening onto an enclosed porch or paved terrace, are often built as an integral part of the house chimney (fig. 41). The corner of boundary walls permits effective treatment. Such fireplaces should meet the regulations of local fire authorities and be built with the same care and be subject to the same rules as inside fireplaces.

OBTAINING PLANS

Plans for outdoor fireplaces are available from various publishing houses; several magazines feature illustrations that can be adapted to the material at hand. If a structure is to be built with local labor and material, simple designs are advisable. The size of stones, joints, and proportions have a direct influence upon appearance, and good personal taste frequently results in more pleasing structures than blind adherence to conventional designs. The various combinations of ovens, cranes, grilles, storage compartments, benches, lights, sinks, etc., to be used as built-in features affect the design. Before planning a structure with these features, catalogs of dealers in outdoor fireplace equipment should be consulted for sizes of the available accessories so that ample space and proper details can be provided in the masonry for building them in. Skilled labor should be employed for elaborate designs (fig. 42) when much equipment is built in or when the fireplace, as in figure 41, is an integral part of a permanent building.

CONSTRUCTION

Ordinarily the fire is built on the hearth, no grate being used. Fire regulations in hazardous localities may require firing doors, dampers, spark screens, and a solid-plate cooking surface; otherwise these features are not essential. Two and a half square feet of cooking surface is desirable, while access to both sides and the end permit several people to cook at the same time. The side walls should have fairly level tops for pots and pans. Side walls are made 2 to 6 inches higher than the cooking level to permit anchoring the grille; if too high, they interfere with cooking. Commercial grilles are available, but satisfactory ones can be made of ½-inch to ¾-inch pipe or ⅝-inch reinforcing rods. The pipes should be 6 to 10 inches longer than the width of the firebox; they should be spaced not more than 1¼ inches apart and have their tops exactly level to prevent pots and pans from wobbling. Two or three pipes can be used for a lintel over the opening into the flue if regular iron lintels are not available. Where a solid top is desired, it should be of boiler plate at least ¼-inch thick. Such plates must be stiffened to prevent buckling by alternate heating and cooling; for ordinary purposes they are merely set on top of the grid though they may be hinged at the rear so they can be tipped back against the chimney.

The best draft is secured when the fireplace faces the direction of prevailing breezes and is protected from strong winds which might scatter sparks. If the fireplace is built too near shrubbery or under trees, the heat and smoke may damage or burn the foliage. A slight rise or a gentle slope that affords good drainage should be selected. 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. Most grilles are set 15 to 24 inches above the ground, though 30 inches may be desirable to avoid the necessity of stooping when cooking. The hearth should slope 1 to 2 inches toward the front so that rain water will drain away.

The area of the chimney flue should be at least one-eighth the vertical cross-sectional area of the firebox.

Fire-clay linings for the firebox and flue are not absolutely necessary except when required by fire regulations or where hot fires are maintained for long periods. They, or common brick linings, are advisable for the more permanent and expensive structures or where it is necessary to use porous stone, such as sandstone and most stratified rocks, which absorb water and flake or chip upon exposure to fire.

Most rocks or stone that can be worked up without special tools or skill, brick, and concrete are adaptable for the average fireplace (fig. 43). The size of the stones determines the thickness of the walls; no wall should be less than 8 inches thick.

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. Concrete made in the proportions 1:2½:4 will serve most purposes where wall sections are about 8 inches thick. For heavy foundations and thick walls not subject to direct fire, 1:3:6 concrete is strong enough.

A concrete slab 4 to 8 inches thick with the bottom 4 to 6 inches below the surface provides a sufficient foundation for medium-sized structures where frost is negligible and the soil is well drained and firm. If the soil is not well drained a 6- to 8-inch layer of stone, cinders, or sand should be provided under the slab and the surface of the immediate vicinity graded or otherwise protected from water. It is advisable to use ¼-inch or ½-inch reinforcing rods, 6 inches apart in both directions, one-third the distance from the top in slabs for all but the smallest fireplaces or where frost is not severe.

Heavy and expensive structures, especially those having tall chimneys, should have foundations below the surface affected by frost or erosion and strong enough to prevent settlement or cracks. Such a foundation can be made of concrete, with a liberal use of large stones for economy, extending under the whole structure, or be continuous walls with a footing similar to those used for houses. The advice and help of builders may save money in the construction of foundations of large expensive fireplaces, especially where climatic conditions are severe and the bearing power of soil is not known.

OPERATION

BARBECUE PITS

DUTCH OVENS

Dutch ovens (fig. 25) are often built in connection with both indoor and outdoor fireplaces to copy early kitchen fireplaces or for actual baking.

When used as an ornament, the oven is fitted with a cast-iron door, and the space thus formed may be used for wood storage. An open firebox or compartment below may be similarly used. Spaces used for wood storage should be separated from the fireplace by a brick or stone partition at least 8 inches thick, all joints being completely filled with mortar.

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. A separate flue with a damper is recommended. For ovens of ordinary size an 8½- by 8½-inch flue is ample. The oven is preheated by fire or hot coals. Before food is placed in the oven, the coals and ashes are removed through the ash drop.

Figure 44 shows a Dutch oven made of tapered adobe bricks and plastered outside with adobe mud. A hole in the top permits the escape of smoke, while the orño is being heated by the fire built inside on the floor. This hole is closed with an adobe block after the coals are raked out. When loaves of bread have been placed on the floor with a wooden paddle, the door hole is stopped with adobe brick.