Assessments - 3, GPA: 4
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Facilidade de uso
A building can be considered as being of tight construction when: 1. Walls and ceilings exposed to outside atmosphere have a continuous water vapor retarder with a rating of 1 perm or less with openings gasketed or sealed, and/or 2. Weatherstripping has been added on operable windows and doors, and/or 3. Caulking or sealants are applied to areas such as joints around window and door frames; between sole plates and floors; between wall-ceiling joints; between wall panels; at penetrations for plumbing, electrical, and fuel lines; and at other openings. If combustion and ventilation air must be supplied to an unconfined space from outside, an opening with a FREE AREA of not less than 1 sq in. per 1000 Btuh of total input of all appliances within unconfined space (but not less than 100 sq in.) must be provided. This opening must be located such that it can not be blocked at any time. IV. CONFINED SPACE A confined space has a volume of less than 50 cu ft per 1000 Btuh of the total input rating for all appliances installed in that space. When furnace is installed in a closet or enclosure, 2 ventilation openings, with OPEN AREA as dimensioned in example below are required for combustion air. The openings should be located about 6 in. from top and bottom of enclosure at front of furnace. (Refer to Table 3.) TABLE 3—COMBUSTION AIR FROM CONFINED SPACE 369RAN FURNACE LENGTH HEIGHT INPUT BTUH (IN.) (IN.) 70,000-105,000 16 8 119,000 20 10 NOTE: In calculating free area, consideration shall be given to blocking effect of louvers, grilles, or screens protecting openings. Screens used shall not be smaller than 1/4 in. mesh and shall be readily accessible for cleaning. If free area through a louver or grille is known, it shall be used in calculating size and free area specified. If design and free area are not known, it may be assumed that wood louvers have 20 percent free area and metal louvers and grilles have 60 percent free area. Louvers shall be fixed in open position or interlocked with furnace so they open automatically at furnace start-up and remain open during furnace operation. The size of the openings depends upon whether the air comes from outside of the structure or an unconfined space inside the structure. A. All Air from Inside the Structure For a confined space, where air is taken from an interior space, 2 permanent openings of equal area are required. One opening must be within 12 in. of ceiling and the other within 12 in. of floor. Each opening must have a free area of at least 1 sq in. per 1000 Btuh of total input rating but not less than 100 sq in. (Refer to Table 4.) TABLE 4—COMBUSTION AIR FROM UNCONFINED SPACE 369RAN FURNACE INPUT BTUH FREE AREA PER OPENING (SQ IN.) 70,000 100 91,000 100 105,000 105 119,000 119 140,000 140 154,000 154 B. All Air from Outside of Structure If outside air is supplied to a confined space, then the 2 openings must be equal and located as above. 1. If combustion air is taken through a permanent opening directly communicating with the outdoors, the opening shall have a minimum free area of 1 sq in. per 4000 Btuh of total input rating for all equipment in the enclosure. 2. If combustion air is taken from outdoors through vertical ducts, the openings and ducts MUST have at least 1 sq in. of free area per 4000 Btuh of the total input for all equipment within the confined space. (Refer to Table 5.) —4— TABLE 5—COMBUSTION AIR FROM OUTDOORS THROUGH VERTICAL DUCTS 369RAN FURNACE INPUT BTUH FREE AREA PER OPENING (SQ IN.) ROUND PIPE (IN. DIAM) 70,000 17.5 5 91,000 22.8 6 105,000 26.3 6 119,000 29.8 6 140,000 35.0 6 154,000 38.5 6 3. If combustion air is taken from outdoors through horizontal ducts, the openings and ducts MUST have at least 1 sq in. of free area per 2000 Btuh of the total input for all equipment within the confined space. (Refer to Table 6.) When ducts are used to supply air, they must be of the same cross sectional area as free area of openings to which they connect. The minimum dimension of rectangular air ducts must not be less than 3 in. TABLE 6—COMBUSTION AIR FROM OUTDOORS THROUGH HORIZONTAL DUCTS 369RAN FURNACE INPUT BTUH FREE AREA PER OPENING (SQ IN.) ROUND PIPE (IN. DIAM) 70,000 35.0 7 91,000 45.5 8 105,000 52.5 9 119,000 59.5 9 140,000 70.0 10 154,000 77.0 10 C. Duct Work Recommendations WARNING: When supply ducts carry air circulated by furnace to areas outside spaces containing furnace, return air MUST also be handled by a duct sealed to furnace casing and terminating outside space containing furnace. Incorrect duct work termination and sealing will create a hazardous condition which could lead to bodily harm. CAUTION: Return-air grilles and warm air registers MUST NOT be obstructed. The proper sizing of warm air ducts is necessary to ensure satisfactory furnace operation. Duct work should be in accordance with the latest editions of NFPA-90A (Installation of Air Conditioning and Ventilating Systems) and NFPA-90B (Warm Air Heating and Air Conditioning System...