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514 CHAPTER 35 1959 Guide The following minimum performance requirements are stipulated: 1. Adequate provision for ease of lighting nH insurance against loss of ignition prior to heating of burner. 2. Base of operation of controls. 3. Proper operation of burner without excessive carboniza tion with grades of oil recommended by the manufacturer. 4. The heater shall be capable of passing the 6 percent ICHAM smoke test. 5. The heater shall be capable of operating with an overall efficiency of not less than 70 percent under conditions of test, or at a lower stack draft recommended by the manufacturer. Design Considerations Same factors important in the design of oil-burning heaters are: 1. Proper pitch of oil lines from the sump to the burner, thus preventing vapor and air lock. 2. Proper positioning of the oil sump or constant-level valve to maintain the proper oil level in the burners, if factory as sembled. 3. Tight construction, not only of oil 1 but of oil *nlr sump, and burner to prevent a hazardous condition due to oil leafage. 4- Provision for leveling and aligning the entire heater for maintenance of proper operation. If a separate fuel is used, the heater should have provision for secure fanning to the floor to prevent excessive strain oq oil supply line, and the consequent danger of leakage of oil. 5. Provision of a draft regulator to prevent abnormal draft fluctuations. 6. Proper shielding of an attached fuel oil supply prevent excessive oil temperatures. to 7. All metal parts subjected to'the corrosive action of the oil mall be made of noncorrodibk metal, or of metal suitably coated to resist corrosion. 8. 11a heater should have suitable baffling or insulation to prevent overheating of floors and walls. 9. Strength in assembly to prevent transportation and use GAS HEATERS Vented gas heaters are defined as those capable of remov ing 90 percent of the flue gases through a single flue outlet. All heaters having a gas input rating in excess of 50,000 Btu per hour must be of the vented type in order to' meet ASA Approval Requirement* for Goa-Fired Room Heater** Space heaters may be classified by burner type as follows: 1. Injection Burner type which employs the energy of a jet 0i Urdus' *** *or com^ust`on into the burner and mix it 2. Yellow Flame Burner type in which secondary air only is depended on for the combustion of the gas. Materials and Construction Standards covering materials and accessories used in the construction of gas heaters are described in ASA Approval Requirement* for Gas-Fired Room Heaters? and in applica ble Listing Requirements." Efficiency Requirement Vented space heaters having input ratings in excess of 20,000 Btu per hour are required to have a heating efficiency of not less than 70 percent based on the total hearing value of the gas. Vented space heaters having input ratings of 20,000 Btu per hour or less are required to have a heating efficiency of not less than 65 percent.' These effinipnciftq are based upon the following equation: where . = 100 -- -- X 100 q (10) et " heating efficiency, percent. H/ = heat above room temperature carried away by the flue products, Btu per hour. q = hourly gas heat input, Btu per hour. Radiant heaters are required to have a radiant efficiency of not less than 28 percent. Design Considerations Some factors important in the design of gas heaters are: 1. Proper design of the burner head, port sizes, and locations so that toe flame will not lift, float, or back, anH be ex cessively noisy in operation. 2. Proper venting of combustion chamber for relief of forces resulting from ignition of an explosive mixture of and air. 3. Protection of valve handles to prevent excessive tempera ture rise during operation. 4. Insulation and baffling of heater to prevent overheating of walls and floor. INSTALLATION OF SPACE HEATERS The two most important considerations involved in the installation of a space heater are safety and chimney draft. The items of chimney details and flue connections which should have special attention are outlined in Chapter 36, Chimneys and Draft Calculations. In &Q cases, it is recom mended that installation be made in accordance with the current National Building Code. REFERENCES 17 -- B -- R Testing and Rating Code for Lout Pressure Heat ing Boilers (Institute of Boiler and Radiator Manufacturers. July 1952). '.Testing and rating code for boiler-burner units (Engineering Standards Part II, Mechanical Contractors Association of Amer ica, 1956). * I -- B = R Ratines for Cast-Iron Boilers (Institute of Boiler and Radiator Manufacturers, May 10, 1955). * 1^ recommendations for heating boilers (Engineering Standards Part II, Mechanical Contractors Association of Amer ica, 1956). * Comfort Healing (American Gas Association, 1938, p. 35). * Gravity Code and Manual for the Design and Installation of Gravity Warn Air Heating Systems (National Warm Air Heating and Air Conditioning Association, J{0 5 gth ed.). necommenoea lorms lor municipal nH fire codes are included in Code and Manual for Design and Installa tion of Warm Air Winter Air Conditioning Systems (National Warm Air Heating and Air Conditioning Association, Manual 7, 4th ed.). A. Landry and R. A. Sherman: Development of a design of smokeless stove for bituminous coal (ASME Annual Meet ing, 1948). * American Standard Approval Requirements for Gas-Fired Room Heaters (American Standards Association, Z21 J1..1054). * American Standard Listing Requirements for: Automatic 20, 1951); Gas Appliance Thermostats (Z21.23, ;2;!v; D,om**txc. Gas Appliance Pressure Regulators (Z21.18, 1956); Automatic Valve* for Gas Appliances (Z21.21, 1952); (American Standards Association). if CHAPTER 36 CHIMNEYS AND DRAFT CALCULATIONS Draft Definitions, Theoretical Natural Draft, Factors Affecting Natural Draft, Available Draft, Required Draft; Industrial Chimneys, Available Draft for the Industrial Chimney, Determining Industrial Chimney Sizes; Residential Chimneys, Available Draft for Residential Chimneys, Short Chimneys, Determining Residential Chimney Sixes, Draft Require ments of Appliances, Chimneys for Gas Appliances; Recommendations of the National Board of Fire Under writers, General Considerations RAFT is the pressure difference associated with the FACTORS AFFECTING NATURAL DRAFT D -movement of flue gases through a flue or chimney. As indicated in both Equations 1 and 2, the theoretical Natural draft is caused and measured by toe difference innatural draft is directly proportional to the height of the flue weight of a column, of flue gas within the flue and a corre and is dependent upon toe absolute mean temperature of the sponding <*nbimn of air of equal dimension outside toe flue. gases within the flue. It is also directly proportional to the Natural draft is always negative and is expressed in inches of density of the air outside the flue although toe effect of this water gage. factor is minor. When the movement of air is supplied by a fan, the draft is The formulas for theoretical natural draft are based on said to be forced or induced. When the fan is located so as to main or average temperature which is one half of the sum push the flue gases through the flue, the draft is forced. When of the entering and exit temperature. Since the difference in toe fan is located so as to draw the flue gases through the exit and entering temperatures, or the temperature gradient flue, the draft is induced. in the flue, is due to the escape of heat through the walls of THEORETICAL NATURAL DRAFT the flue and chimney, the heat transfer characteristics of the chimney construction affect draft. Heat transfer is also af Theoretical natural draft is produced solely by the differ fected by the rate of flow of toe flue gases through toe flue ence in weight of the column of flue gases within the flue and that of a corresponding column of air of equal dimensions so that draft is also affected directly. The flow of flue gases through the flue is retarded by fric outside the flue. In the determination of theoretical natural tion which varies directly with the friction coefficient of the draft, no allowance is made for friction 01 other positive or flue surface,'and with the rate of flue-gas flow. The friction negative effects. Theoretical natural draft is expressed by the loss may be estimated by means of one of the formulas for following formula: ducts such as the Fannmg equation or it may be estimated with sufficient accuracy by toe method used for air ducts. D, - 2.96 HB. (1) (See Chapter 21.) The height of the flue is measured from the point of en where trance of the flue gases to the top of the flue. With no wind to produce an aspirating effect and with no obstruction such D, -- theoretical draft, inches of water. as a rain cap at the top of the flue, the column of flue gases H " height of flue or chimney, feet. may extend upward above the top of the flue for several B - barometric pressure, inches of mercury. p, *= density of air at 0 F and 1 atmosphere pressure, pounds feet. The effect of this column may be sufficient to overcome the negative or retarding effect of friction and to cause the per cubic foot. observed draft to exceed the theoretical draft. This added p. ** density of flue-gas at 0 F and 1 atmosphere pressure, effect has been measured in some test work. A wind blowing pounds per cubic foot. T, > temperature of air surrounding the chimney, Fahren across the top of the flue may also produce an aspirating effect sufficient to overcome the effect of friction and to cause the heit absolute. observed draft to exceed the theoretical. Both of these effects T, temperature of the gases, average or effective, in the are transient and unreliable and should not be considered in chimney, Fahrenheit absolute. determining the proper design of a chimney. Theoretical natural draft may also be expressed by-the following simplified formula in which it is assumed that the densities of the flue gas ami of the air are equal at the same temperature and pressure: PH(TC - T.) 52T, (2) where p mean density of atmospheric air, pounds per cubio foot. AVAILABLE DRAFT The available draft produced by any chimney is equal to the theoretical natural draft minus the friction loss. Given the height, the heat transfer characteristics of the chimney construction, the entering temperature of the flue gases and their volume, and toe friction coefficient of the flue and its dimensions, toe available draft is readily calculable. The efficiency of a chimney is defined as the ratio of the observed draft or available draft, produced by toe chimney 515 1