Document 06ek4mM1EM5jBbGQgxaZ3YB0d

392 CHAPTER 16 1950 Guide Table 4. Drafts Required by Typical Domestic Heating Devices or Appliances Device Warm Air Furnace, Oil Burning, Pot Burner.................... Mechanical Oil Burner, More than 5 gph----------------------- Draft, Inches Water 0.06 to 0.08 0.06 0.06b 0.06 0.03a 0.05a or less 0.04b 0.06b Stack Temperature F Deg 1000 860 900 860 400 900 * Draft in firebox. b For chestnut sized anthracite. CHIMNEYS FOR GAS HEATING Heating appliances designed to bum gas as well as appliances converted to gas burning, except those equipped with power type burners and ex cepting conversion burner installations in excess of 400,000 Btu per hour input in large steel boilers, are always equipped with a draft hood attached to the flue outlet of the appliance. This draft hood is required if the appliance is to meet the approval requirements of the American Gas As sociation and the American Standards Association, and is essential for safe operation. It is designed to prevent excessive chimney draft which would lower appliance efficiency, to prevent a blocked flue or a down-draft in the chimney from impairing combustion, to provide a relief opening for the products of combustion during down-draft or blocked flue conditions, and to prevent spillage of the products of combustion to the space surrounding the appliance, if there is a chimney draft equivalent to that provided by a 3-ft chimney. As the draft hood is designed without moving parts, the relief opening is always open, and consequently some air is drawn into the chimney. While the air drawn in lowers the gas temperature in the chim ney, it also lowers the dew-point of the gases and tends to prevent , con densation. The installation of conversion burner equipment in large boilers is usually made in accordance with regulations of the local gas company. In such installations a definite chimney draft may be required for proper combustion, and consequently the foregoing reference to the use of draft hoods would not apply. The products of complete combustion of gas are water vapor (HjO) and carbon dioxide (C02). In the case of manufactured gas, the presence of organic sulfur compounds, generally between 3 and 15 grains per hun dred cubic feet, gives rise to minute percentages of sulfur dioxide and sulfur trioxide. The volume of water vapor in the flue products from natural or coke oven gas is about twice the volume of carbon dioxide. , It is extremely important that the chimney be tight and resistant to corrosion, not only from moisture, but also from dilute sulfur trioxide. Clay linings with joints which prevent retention of moisture and lin ings made of non-corrosive materials, are advantageous. The protection of unlined chimneys has been investigated and the results indicate that after the loose material has been removed; spraying with a water emulsion of asphalt chromate will provide excellent protection. Chimneys and Draft Calculations 393 'Advice regardingrecommended practice'and materials for flue connec tions and chimney linings can usually be obtained from the local gas com pany, and should be given careful consideration. - Since a gas-designed appliance must be able to operate at rated input5 (plus 10 or 15 per cent) without chimney connection, and without pro-' ducing carbon monoxide, the only function of the chimney is to remove the products of combustion from the room. The chimney provides draft to Fio. 7. Allowable Btu Input to Circular Flues for Domestic Gas.Appliances. with Draft Hoods 'j NOTES APPLYING TO FIG. 7: (1. Chart is based on: average flue temperature of 150 F, outside temperature of 60 F, barometric pressure of 30 is. Hg, -100 per cent excess air and 100 per cent dilution at draft hood. , 2. Based on terra-cotta lined flues.' Withrough brick flues.capacities are 15 percent less. 3. Based on condition that horizontal run is not greater than 20 ft exoept for a flue height less than 20 ft, in which case the horizontal run is not to have greater length than the height of the flue. 4. Two long radius elbows are included in the horizontal run, the diameter of which is equal to that ofthe flue. 5. Each additional elbow reduces the allowable horizontal run by a length in feet equal to the diameter |n inches. 6. When the horizontal run has an effective length in excess of that given (or additional elbows) the nextlarger size of flue should be chosen. . It is desirable that long horizontal runs be insulated to reduce heat loss of. flue produote and to conserve draft. - 7. Capatitieasbouldbereduced3.6peroent foreach 1000 ft above sea leveL