CHIMNEY AND FIREPLACE CONSTRUCTION Correct chimney construction is absolutely essential to economi cal home heating. The ideal and most efficient chimney is vertical, with round flue and smooth interior surfaces (fig. I). All chim neys should be built with "fire-clay" flue linings (not "flue-tile," "terra-cotta" or "clay" flue lining). Faulty chimney construction practically always shows its shortcomings by its effect upon some other feature of the plant. A lighted paper thrust in the bottom and sucked up and consumed with a roar is often erroneously taken to indicate a good draught. Chimney draught can be known definitely only by measurement with the proper instrument, a draught gage. Chimney height and temperature inside and out side the chimney determine intensity of draught in a correctly built chimney.
Factors that contribute to faulty chimneys are : (z) Insufficient height to assure proper draught and avoid interfering air currents (fig. 2) ; the top of a chimney should extend at least 3f t. above flat roofs and at least 2 f t. above the ridge of peaked roofs; exten sions, if used, should be fitted with air-tight joints; (2) omission of flue-lining to ensure continued tightness, so that heat and weathering cause mortar gradually to disintegrate and result in a leaky chimney (fig. 2) ; (3) offsets and bends are likely to reduce the chimney free area and present difficulties in construction that militate against tightness and inside smoothness; loose bricks and mortar may fall and lodge in such a way as to cause objectionable restricted areas and 'provide lodgement for dangerous soot accu mulations (fig. 2) ; (4) careless and improper installation of the smoke pipe into the chimney (fig. 3) ; (5) openings into a chim ney for other than the smoke pipe of the boiler ; such should never be permitted, they are apt to check and interfere with the draught ; (6) lack of a tightly-fitting cover for the clean-out door; (7) fail ure to support the chimney properly ; it should never be based on timber construction and when resting upon the ground sufficient masonry foundation should be provided to prevent settling; (8) improper laying of brick ; it should never be laid on edge, should be properly bonded and sufficient mortar used between the bricks to fill all voids. Size and height of chimneys depend upon the total heat demands of the structure to be served, the type and number of boilers and the fuel to be used. Reputable manufacturers spe cify draught requirements for their respective equipment and state the required flue areas, sizes and heights of chimneys ; these should be observed. Irrespective of fuel used, the minimum effec tive area' inside the flue lining for any installation should be not less than 7o sq.in. and the short cross-sectional dimension should be never less than six-tenths of the greater dimension. The mini mum chimney height above the grate should be 3 5f t. if erratic draughts are to be avoided.
A chimney that is not tight will fail to draw properly. Force 'Effective area of a flue, broadly speaking, is the theoretical cross sectional area occupied by the column of smoke and gases rising with spiral motion up the flue.
or direction of wind, the amount of moisture in the air or the qual ity of the fuel may aggravate the trouble. A smoke test will prove leaks and every flue should be tested before a boiler is con nected thereto, by building a paper, straw, wood or tar-paper fire at the base of the flue. When the smoke is passing in dense volume if the stack be tightly blocked by laying a wet blanket over it, the leakage will be immediately evident by the appearance of smoke at the opening, or from an adjoining flue indicating leakage between the flue joints.
If a leakage is not obviously evident, further inspection by means of a mirror held at the proper angle at the base of a straight flue should be made for minor obstructions such as broken tile, mortar accumulations, birds' nests, partly burned paper, soot or tarry deposits ; or removal may be accomplished by passing up and down the flue a weighted bag of hay or straw attached to the end of two ropes.
Correct throat construction is essential, to avoid a smoky fire place and to provide for proper velocity of the outgoing gases. The area of the throat should be not less than that of the flue, its length always equal to the width of the fireplace opening (fig. 4) ; the sides of the fireplace should be vertical until the throat is passed (fig. 4) ; and above the throat, the sides should be drawn in until the desired flue area is obtained; the throat should be not more than 4 or Sin. in width and set Bin. above the lintel of the opening (fig. 4). The use of a throat damper is advisable; if omitted, the throat opening should be 4in. and the smoke shelf always included. A smoke shelf and chamber are absolutely essen tial. The shelf is formed by setting back the brick work at the top of the throat to the line of the flue wall, making the shelf equal in length to that of the throat. No shelf should be less than 4in. and may vary from this to i gin. or more, depending on depth of fireplace ; the level of the shelf should be 8in. above the fire place opening (fig. 4). The smoke chamber acts as a reservoir to hold accumulated smoke temporarily when a gust of wind across the chimney top momentarily dampers the chimney, as well as to lessen the down draft and prevent smoke being forced into the room. All smoke chamber walls should be smooth inside. The back of a fireplace should pitch forward from a point a little less than half-way from the hearth to the top of the open ing and the sides should be beveled, as straight back and sides do not radiate heat as well.
The use of a throat damper affords means for regulating a fire. The type with lid hinged at rear, rather than in the centre, directs better the outgoing smoke into the flue. Full opening is required for fast-burning pine ; slow-burning hardwood logs require only I or tin. openings. Fireplace openings should be kept low, 3oin. minimum and 42in. maximum height. The higher the opening, the greater the possibility of a smoky fireplace; the width of opening should be slightly greater than the height ; a minimum depth of i8in. is advisable although i 2in., in small fireplaces, will provide a good draft with properly constructed throat.
Efficiency of fireplace heating can be improved materially by the use of a fireplace heater which heats all incoming air before it enters the room. These devices consist of an intake air mani fold, into which air from the outside is drawn and delivered into heat pipes lining the rear wall of the fireplace, from which it passes into a heated air manifold and is then delivered into the room directly above the fireplace openings at temperatures varying from 135° to 195° F. Tests have shown that the use of a proper fireplace heater is the means of increasing measurably the effec tiveness of fireplace heating, through, (I) raising the room tem perature 3/ times as quickly as can be done with the bare fire place, (2) maintaining a far more even temperature throughout the entire room, (3) avoiding cold air leakage through window and door cracks and (4) by producing a greater heating effect with less fuel than when no heater is used. (A. M. D.) See J. J. Norman, Design of a Brick Chimney (1913) ; J. G Mingle, Draft and Capacity of Chimneys (192 5) ; A. Custodis, Radical Brick Chimneys (5924).