WW-F-2743A
3.10 Heat exchange surfaces. Heat exchange surfaces shall include the combustion chamber (primary heating surface) plus any secondary surfaces, such as wrap-around radiators, box-type panels, or tube sections, interposed between the combustion chamber and the flue-gas stack connection. On gas-fired units with multiple, manifold-connected burners, combustion chambers may be die-formed integrally with supplemental heat transfer surfaces to provide a unitized, multi- section clam-shell type heat exchanger. All heat exchangers shall be gas-tight construction, designed, and installed to allow the metal to expand and contract within the casing without developing leaks or causing damage to associated parts. Combustion chambers and secondary heating surfaces shall be constructed of materials and sheet metal gages acceptable under UL or ANSI standards for the maximum temperature which the surfaces are exposed at specified test temperatures. Refractory used for chamber linings shall be of the castable, performed type consisting primarily of alumina, silica, or magnesia compositions with the suitable binders. Refractory linings shall be rated to withstand temperatures to 2500 F (1 371 C) and shall be replaceable with a minimum of disassembly.
3.11 Burners and fuel systems.
3.11.1 Oil. Group 1 and group 2 oil burner shall be of the high-pressure or low-pressure atomizing type in accordance with UL 296. Group 3 oil burners shall be of air or mechanical atomizing type, conforming to UL 296. Burners shall be designed to fire fuel oil conforming to ASTM D 396 grades number 1 and number 2 for burner types LO and GLO and grade number 4 for burner types HO and GHO. The burner shall be completely automatic and shall include a motor, combustion air blower, ignition system, fuel pump, burner tube, and for group 3 units, a safety shutoff valve. Combination burners shall be designed for selective burning of either gas or grade number 1 or number 2 fuel oil. Both oil burners and combination burners shall be UL listed.
3.11.2 Gas. Type I, group 1 and group 2 gas burners shall meet the requirements of
ANSI Z21.47. Type II, group 1 and group 2 shall meet the requirements of ANSI Z83.8 as specified in 3.7(b). Type I, group 3 gas burners shall meet the requirements of UL 795 or ANSI Z21.47 and type I, with ANSI Z83.8 as specified in 3.7(b). Burners shall be designed, adjusted, rated, and certified to fire natural, manufactured, mixed, or propane gas, as specified (see 1.2.3). Burners shall be rated for use at altitudes to 2,000 feet (609.6 m) unless higher altitudes are specified (see 6.2). Gas pressure regulators shall be furnished for all units.
3.12 Ignition systems. The ignition systems shall comply with the applicable provisions of UL 296, UL 795, ANSI Z21.47, and ANSI Z83.8. Burners shall be equipped with ignition systems as follows:
a. Ignition systems for group 1 and group 2, gas-fired units, shall be of the direct spark, intermittent or interrupted types with electrically-ignited proven pilots or shall be of the pilotless hot-surface ignition type. Continuous pilots shall not be permitted.
b. Ignition systems for group 3 atmospheric gas burners shall be intermittent or interrupted type in accordance with ANSI Z21.47. Ignition systems for group 3 power gas burners shall meet UL 795 or ANSI Z83.8.
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