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• <br /> b (z) ,teR. <br /> • <br /> • <br /> TABLE 304.1 <br /> COMBUSTION AIR REQUIREMENTS FOR GAS-FIRED <br /> APPLIANCES WHEN THE COMBINED INPUT IS UP TO <br /> AND INCLUDING 400,000 Btu/lir <br /> • <br /> TOTAL INPUT OF APPLIANCESa, REQUIRED FREE AREA OF AIR-SUPPLY ACCEPTABLE APPROXIMATE ROUND DUCT <br /> THOUSANDS OF Btu/hr OPENING OR DUCT,SQUARE INCHES EQUIVALENT DIAMETER2, <br /> • (kW) (sq mm) INCH(mm) <br /> • <br /> 25 (8) • 7(4,500) 3(75) <br /> 50(15) 7(4,500) 3 (75) <br /> 75(23) • • • . :� .11(7,000) 4(100) <br /> 100 (30) • :1'4(5,000) 4(100) <br /> • . . 125 (37) 18(12,000) 5(125) <br /> 150 (45) 22(14,000) 5(125) <br /> 175 (53) 25(16,000) 6(150) <br /> 200(60) 29 (19,000) 6(150) <br /> 225 (68) 32(21,000) 6(150) <br /> 250(75) 36(23,000) 7(175) <br /> 275 (83) 40(26,000) 7(175) <br /> ' 300 (90) 43 (28,000) • 7(175) <br /> r= 325(98) 47 (30,000) 8(200) <br /> 350(105) 50(32,000) 8(200) <br /> 375(113) 54(35,000) 8(200) <br /> • L. 400(120) 58(37,000) 9(225) <br /> I. For total inputs falling between listed capacities, use next largest listed input. <br /> • : . If flexibleduct is used, increasi the duct diameter by one inch.* <br /> Flexible duct Shall be stretched with minimal sags. • <br /> • <br /> BTU Amount for Non-direct vent appliances <br /> • <br /> 8:k. re c t fioor vtext -� <br /> • Elec_ c_ et-kev' \tveekie <br /> • <br /> • <br /> • <br /> • <br /> • <br /> . <br />