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1 Where provisions for fresh air are required in this section, one of the <br /> following methods shall be used: <br /> 2 <br /> 1. Permanent openings or ducts leading from the water <br /> 3 heater location to other interior areas, except unven- <br /> tilated attics, which meet the minimum required <br /> 4 volume specified in subsection (b) of this section. <br /> 5 If such openings or ducts convey air from an attic space, the attic space <br /> shall be ventilated by fresh air openings or louvers on a vertical wall or at <br /> 6 two different levels or elevations. <br /> 7 2. Permanent openings or ducts leading from the water <br /> heater enclosure to the outside of the building. <br /> 8 <br /> 3. For gas-burning water heaters, all openings or ducts <br /> 9 shall have a total unobstructed area not less than that <br /> shown in Table 23-1. <br /> 10 <br /> For heaters burning solid or liquid fuels, the required areas shall be one <br /> 11 and one-half times those required for gas-burning heaters. <br /> 12 A minimum of six (6) inches unobstructed space across the entire front of <br /> the water heater shall extend from the floor to at least the top of the <br /> 13 appliance. <br /> 14 Areas of ducts or openings shall be equally divided with one-half (Y2) of the <br /> total required area within the upper twelve (12) inches of the appliance <br /> 15 enclosure and one-half (Y2) not more than twelve (12) inches above the base <br /> of the lowest appliance within the enclosure. Required openings shall not <br /> 16 be less than three (3) inches in least dimension. <br /> 17 (d) Louvers and Grilles <br /> 18 In calculating free area of all louvers and grilles, consideration shall be <br /> given to the blocking effect of louvers, grilles or screens protecting <br /> 19 openings. Screens used shall not be smaller than Y4 inch mesh. If the free <br /> area through a design of louver or grille is known, it should be used in <br /> 20 calculating the size opening required to provide the free areas specified. <br /> If the design and free area is not known, it may be assumed that wood <br /> 21 louvers will have twenty to twenty-five (20-25) per cent free area and <br /> metal louvers and grilles will have sixty to seventy-five (60-75) per cent <br /> 22 free area. <br /> 23 (e) Alternate Methods of Supplying Combustion Air <br /> 24 In lieu of requirements of Table 23-1, combustion air supply may be <br /> designed in accordance with recognized engineering principles when first <br /> 25 approved by the Building Official. <br /> 26 <br /> 27 <br /> 28 <br /> 29 <br /> 30 <br /> 31 <br /> 32 <br /> - 16 - <br />