Document 5kj6jK4n9bmg1dnmDrY2ZmeNR

844 CHAPTER 53 1965 Guide And.Data Book 8 at the percentage CO*, moving horizontally to the curve for- the type of fuel, and then moving, vertically downward to the weight of products per 1000 Btu, the reader can determine the flue gas rate in pounds per hour for any fuel.* Any of the described methods of determining available draft may be used, but)a graphical solution to the problem may be obtained for an 8 X 8-in. chimney from Figs. 2,8, and 10. This solution can be best explained by a numerical example.. Example 4: Determine whether a 13-ft, 8 X 8-in. nominal-size flue is sufficient for a coal-heating unit rated at 0.03 in. of watodraft at 400 F inlet temperature, fuel rate being 10 lb per hr of bituminous coal, with 10 percent CO*. Solution: From fig. 8 a Sue gas rate of approximately ISO lb per hr is obtained-iThe available draft for a 180 lb per hr gas flow, and an inlet temperature of 400 F, obtained from Fig. 10, is 0.056 in. of water. This indicates that the chimney is adequate. The selection of chimney areas for liquid- and solid-fuel- burning devices is difficult because of the variability in-effi ciency of different models, the possibility that soot on the lining will restrict the chimney area, and the variation in combustion air requirements of different solid fuels. Figs 2 and 10 show that a given chimney produces a maximum avail able draft and a maximum efficiency for some intermediate mass flow rate for any selected inlet flue gas temperature. For mass flow rates lower than optimum,- the greater cooling of the gases in the chimney causes lower available draft, whereas, for mass flow rates above the optimum,' the greater friction lossee reduce the available draft. A chimney for a given heating system should probably be designed to operate at its point of - maximum efficiency and maximum available draft for its full rated output. A chimney would have an accelerating effect1* on the combustion rate of a solid-fuel burning device if the chimney were operating to the left of the optimum point in Fig. 10, because an additional increment in mass flow rate would increase the available draft a' email amount nd tend to increase the mass flow still more. On the other hand, a chimney operating,to the right of the optimum point in Fg. 10 would tend to decelerate the combustion rate for-any small increase in mass flow rate. Data are not complete for the selection of.proper chimney areas for heating plants of different capacities, but some in formation on the effect of cross-section areas on the capacity of masonry chimneys is provided by tests*-** on several chim neys with liners having nominal outside dimensions: 9-in. diameter, 12-in. diameter, -9 X 9-in., and 9 X 13-in. These tests showed that, for flue gas rates up to 200 lb per hr, and entering flue gas temperatures from 200 to 1000 F, the 9-in. round liner provided an available draft equal to, or greater than, that produced by the other three larger liners. When the flue gas rate was increased to 320 lb per hr, the three larger liners produced a little more draft than the smallest one for entering flue gas temperatures above 600 !F. Other data1* show that metal chimneys with an internal diameter of 6 in. should not be used for ma-<a* flow rates greater than 130 lb per hr. Table 5 shows approximate values of the ma.st flow rates and flue-gas velocities at the chimney inlet that produce the maximum available draft for masonry chimneys* of several conventional sizes and with an effective height of 15 ft. This table shows that a 9-in. round chimney is best suited to mas* flow' rates from-130 to 170 lb per hr; a 9 X 9-in. chimney performs best for flow rates from about 200 to 300 lb per hr. and 9 X. 13-in. and 12-in. round chimneys are best suited to flow rates above 300 lb per hr. These results were obtained with' clean'chimneys, so that conclusions about chimney areas require some modification if soot deposits are taken into con-! ^deration.' ' "" Soot deposits in chimneys reduce the effective area of the liner and may, in some cases, entirely close the pmag* Soot deposits are likely to be greater in the horizontal passages in the, heating plant, the breeching, and. the smokepipe than in the vertical chimney liner. An increase in the liner diameter of one -inch above that required for a elwm chimney will probably make adequate'allowance for soot deposits in'all but the worst cases. Where smoky combustion is likely to occur and the' mass- flow rates on a clean chimney bass apri proach those listed in Table 5,-the next larger1 commercial size liner should be used. Smoky combustion with oil-burn ing devices, particularly with vaporizing oil burners, b likely to be caused by inadequate draft, which is often due to insufficient chimney height. For coal, inadequate chimney . height or chimney: area may be a contributing qurae, but smoky combustion with coal b related to fuel characteristics and firing methods. Therefore, an .increase in chimney area will usually cot cure smoky combustion of a coal-burning device, but can be expected to lengthen the interval between cleanings. ,, New standard sites of-clay flue linings were developed by the industry and approved by the American Standards As sociation, in order to effect economies that can' be derived from coordination. of the dimensions-of building materiala These linings are known as modular.clay flue linings, and .the dimensions and tolerances are summarized in ASA Standard A62.4-47. As the effective areas of these liners are somewhat nmftlW than those of the corr&ponding lining*. nqed pre viously, they cannot be used in certain municipalities where building codes specify minimum areas Himensinn* on the older . DRAFT, REQUIREMENTS OF APPLIANCES .. Typical flue-gas temperatures and drafts required at rated output for several kinds of.domestic heating appliances0 are contained in Table 6. Chimney height and chimney area for cast-iron boilers are specified in the I -- B * R Testing and Rating Code of the'.Institute of.Boiler and'Radiator Manu facturers. !,, ' l' Mechanically-fired devices such as o3 burners and stokers are equipped with blowers, and the chimney b not required to overcome the resistance of-the fuel bed or burner. Never theless, a draft in.the firebox of about 0.03 in. of water- b desirable so that any leakage will be into the firebox rather than outward from it. Insufficient draft for natural-draft appliances b Kkely Tablet ;5l.... Approximate Hue . Gas How .Rates, for Maximum Available, Draft in Masonry-Chimneys- Ffoe Got Teaperntmei at Oifancy tnlef,'F'' Nominal . fntemof Aria External Liner of liner Dimenriont, la. ' Sq. In. 200 600 ' 1000 'Man How Gate, ib'/Hr 200|600 1000 Am Gat - Vdodly at' Chimney Intel, Fp* 6 (dia) ` 38.5 9x9 49 ' 12 (dia);--' .-; 78.5 9 x 13 77 ` " 170 150 ' 130 215 `3b6/ 334 290 Above - Above 320 320 295 Above" Above .320 320 175 2sd 300 175 400 600 150 -- --.- 150 -- Chimneys and Draft 845. ^rith installations in attics or in on^story basement!ess houses! Automatic oil-burning space heaters, floor furnaces, and warm air furnaces employing natural-draft vaporizing-burherB re quire a draft of 0.06 to 0.08 in. .water for outdoor tempera tures of 60 F. Coal-burning heaters and furnaces which attain .design rating at'O F outdoor temperature would require about the same dri&fti.For such :requireroents,'data from- Fig. l3 and Table 2 show that an effective' chimney height, above'chimney inlet, should be a minimum of 8 to 12 ft. Because temperature drop and-friction-loss in the-iflue pipe.-cannot be; calculated accurately,' and the resistance of various chimney connections b uncertain, the minimum calculated.heights should have a generous factor of safety applied to allow for these and other uncertainties. Where ample height cannot be provided; forced or induced draft should' be provided; Extreme care should be used in the application of forced draft to avoid-producing a pressure-in combustion.'chambers, because!they hare -pot .usually designedto prevent the outward-leakage of:toxic gases which might result. - Induced draft by means of motor-driven, fans or'blowers will solve low-draft problems, but.would usually be employed for residential systems only as. a last resort. Operation of. a blower- entails some -cost, introduces maintenance require ments, and maybe dangerous-in event of po'wer'failure'un4 leas. suitable protective devices] are used. Induced draft fans designed to resist effects of high temperature- and corrosion are available; Fans not carefully designed or modified-.to meet these conditions should not be applied to this service. ", ' J RECOMMENDATIONS OF- THE NATIONAL , BOARD OF. FIRE UNDERWRITERS \ : For-general data on the construction-' of chimneys, refer to tire National'Building Code, recommended by the National Board of fire Underwriters,'-Article X,'Section 1001Jto 1006, in which the following'are some of-the important ,'provisibris . listed in the 1951'editibn:'" *' ' t,.;v . -> 1. Flue Connection* Required. Every heating apparatus.or heat producing appliance requiring a flue connection shall ;be connected with a flue-conforming to the provisionsof this.arti cle. This shall not include '.electric appliances;,,gas. appliances, except as specifically required in this article; or oil fired appli-' mppn Agpfw-iwUy designed for use without flue connection. , . / 2. V*e of Nonconjarming,This*. Flues not conforming to the Table 6 ..".. Drafts-Required by Typical. Residential Heating * :. Devices or. Appliances .'] ' \ i :,..OaWc*,- Draft, fa- Water SU root-.1 peroftire* F 8pace Heater, '.Oil-Burning, Pot Burner................................................ 0.06 to 0.08 Warm Air Furnace, Oil-Burning, Pot Burner............................................... 0.06 Warm Air Furnace, Hand-Fired........ 0.06* Floor Furnace, Oil-Burning, Pot Burner............................................... 0.06 Mechanical Ofl Burner, Les than 5 gpb..................................................... 0.03" Mechanical Oil Burner, More than 5 gph.................................................. 0.05* or less Cooking Stove, Solid-Fuel................. 0.04* Space Heater, Coat-Burning............. 0.06* * Draft in firebox. * Forcbeatavt cited anthracite. * IS in. from beater. 1000 660 900 860 _ -- 400 900 requirements of this article for chimneys, metal smokestacks or vents for gas appliances, shall not be used unless listed by Underwriters' Laboratories, Inc.,' installed in full compliance with the listing and the manufacturer's instructions, and .ap proved for such use by the building-official. 3. Smoke Pipe Connection*. .\ \ a. No flue h* have smoke pipe connections in more than onestory of a building, unless provision is made for. effectively closing smoke pipe openings with devices made of noncombustible materials whenever their use is discontinued temporarily,- and completely closing them with masonry when discontinued per manently., b. Two or more smoke pipes ahall not be joined-for a single connection,. unless, the smoke pipes and.flue are of .sufficient size to serve all the appliances thus connected. c. The smoke pipe of`a heating appliance shall`not be con1 nected into the flue of an incinerator which has the rubbish chute identical with the smoke flue. 4. Construction of Chimney*. , a. Chimneys hereafter, erected within or attached to a struc ture'shall be constructed in compliance with the provisions of this section. b. Chimneys shall extend at least 3 ft above the highest' point where they pass through the roof of the building, and at least 2 ft higher than any ridge within 10 ft of such chimney. , .?, c.. Chimneys shall be wholly supported on . masonry or self- supporting fireproof construction. ' ' ; . d. No chimney shall be dorbeled from a wall more than 6 in.; nor ghil a chimney be corbeled from a wall which is less than -12 in. in thickness, unless it projects equally on each side of the wall; provided that in the second story.of 2-story dwellings cor beling of chimneys on the exterior oi the. enclosing walls may equal the wall thickness. In every case the corbeling shall not exceed 1 in. projection for' each course of brick projected. ; . - e. No change in the size or shape of a chimney, where the chimney passes. through the roof, hwll be made within a dis tance of 6 in. above or below the roof joists or.rafters. - - . i 5..Chimney* for Heating Appliances, Low Heat. Industrial Appliance* and Portable Type Incinerator*. a. Chimneys for. stoves, cooking ranges, warm air,' hot water and low pressure steam beating furnaces, fireplace, arid low heat industrial appliances, other than chimneys for incinerators of nonportable type, shall be constructed of solid masonry units or of reinforced concrete. `Die walls shall be property bonded or tied with corrosion-resistant metal anchors: In dwellings and buildings of like beating requirements, the thickness of;.the chimney shall be not less than' 4 in. In other buildings the thick ness ah*11 be not less than 8 in., except that rubble stone masonry ahall be not less than 12 in. thick. b. Every such chimney hereafter erected* or altered shall be lined with a Sue lining conforming to. the- requirements below. ;;.V Flue lining?* ahall be maHw of fire day or other refractory day which will withstand the action ef flue gases and resist, without softening or cracking, the temperatures towhich they will be subjected, but not less than 2000.F. Flue linings may fc* of oast iron of approved quality, fonn.and construction. d. Required clay flue lining?* shall be not less than 1 in.'thick for the smaller flues, and *nal1 increase in thickness for the larger, flues. 1 1* , e. Flue linings hall be installed ahead of the construction^ of the chimney as it is carried up, carefully bedded one on the other in Type A, Type B, or fire clay mortar with close fitting joints left smooth on the inside. L Flue linings ahall start from a point not less than 8 in. be low the intake, or, in the case of fireplaces, from the throat of the fireplace. They ahall extend, as nearly vertically as possible, for the entire height of the chimney, and be extended 4 in. above the top of cap of the chimney. g. Cleanouts for flues or fireplaces ahall be equipped with cast-iron doors and frames arranged to remain tightly closed when not in use. h. When two or more fluea are contained in the same chim ney, at least every third flue shall be separated by masonry at least 4 in. thick bonded Into the masonry wail of tbs chimney. Where flue lining* are not so separated, the joints of adjacent flue linings shaUbe staggered at least 7 in.