5.When the boiler is installed in a confined space and all air is provided from the outdoors the confined space shall be provided with one or two permanent openings according to methods A or B. When ducts are used, they shall be of the same cross sectional area as the free area of the area of the openings to which they connect. The minimum dimension of rectangular air ducts shall be not less than 3 x 3 inches or 9 square inches.
A. When installing two openings, one must commence within 12 inches from the top and
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| FIGURE 2 |
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| FIGURE 3 |
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the other within 12 inches from the bottom of |
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the enclosure. The openings shall |
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communicate directly, or by ducts, with the |
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outdoors or spaces (crawl or attic) that freely |
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communicate with the outdoors. One of the |
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following methods must be used to provide |
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adequate air for ventilation and combustion. |
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1. When directly communicating |
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with the outdoors, each opening shall have a |
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minimum free area of 1 square inch per 4,000 |
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BTU per hour of total input rating of all |
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equipment in the enclosure. See figure 2 |
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above. |
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2. When communicating with the |
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| FIGURE 4 |
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outdoors by means of vertical ducts, each |
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opening shall have a minimum free area 1 |
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square inch per 4,000 BTU per hour of total input rating of all appliances in the enclosed space. See figure 3 above.
3.If horizontal ducts are used, each opening and duct shall have a minimum free area 1 square inch per 2,000 BTU per hour of total input rating of all appliances in the enclosed space. See figure 4 at right.
B.One permanent opening, commencing within 12 inches of the top of the enclosure, shall be permitted where the equipment has clearances of at least 1 inch from the sides, 1 inch from the back, and 6 inches from the front of the boiler. The opening shall directly communicate with the outdoors or shall communicate through a vertical or horizontal duct to the outdoors or spaces (crawl or attic) that freely communicate with the outdoors. The openings must have a minimum free area of 1 square inch per 3000 Btu per hour of the total
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