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Gable |
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Vent |
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Top Above |
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Inlet (a) |
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Insulation |
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Soffit | Outlet |
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Vent | Air (a) |
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FIGURE 39: Outside and Ambient Combustion Air
Air Supply Openings and Ducts
1.An opening may be used in lieu of a duct to provide to provide the outside air supply to an appliance unless otherwise permitted by the authority having jurisdiction. The opening shall be located within 12” (30.5 cm) horizontally from, the burner level of the appliance. Refer to “AIR SOURCE FROM OUTDOORS AND VENT AND SUPPLY AIR SAFETY CHECK” in these instructions for additional information and safety check procedure.
2.The duct shall be either metal, or a material meeting the class 1 requirements of
3.The duct shall be least the same
4.The duct shall terminate within 12” (30.5 cm) above, and within 24” (61 cm) horizontally from, the burner level of the appliance hav- ing the largest input.
5.A square or rectangular shaped duct shall only be used when the required free area of the supply opening is 9 in2 (58.06 cm2) or larger. When a square or rectangular duct is used, its small dimen- sion shall not be less than 3” (7.6 cm).
6.An air inlet supply from outdoors shall be equipped with a means to prevent the direct entry of rain and wind. Such means shall not reduce the required free area of the air supply opening.
7.An air supply inlet opening from the outdoors shall be located not less than 12” (30.5 cm) above the outside grade level.
Ventilated Combustion Air
The ventilated attic space or a crawl space from which the combustion air is taken must comply with the requirements specified in “AIR SOURCE FROM OUTDOORS” in this instruction or in Section 5.3, Air for Combustion and Ventilation of the National Fuel Gas Code, ANSI Z223.1 (latest edition). This type installation requires two properly sized pipes. One brings combustion air from a properly ventilated attic space or crawl space and a second pipe that extends from the furnace vent connection (top right of unit) to the exterior of the building. Refer to Table 7 for intake pipe sizing, allowable length and elbow usage. Follow all notes, procedures and required materials in the "COMBUSTION AIR/VENT PIPE SIZING" section in these instructions when installing the combustion air pipe from the unit and into a ventilated attic space or crawl space. DO NOT terminate vent pipe in an Attic or Crawl Space.
Ventilated Combustion Air Termination
Refer to Figure 39 for required attic termination for the combustion air intake pipe. For attic termination, use two 90 elbows with the open end in a downward position. Be sure to maintain 12” (30.5 cm) clearance above any insulation, flooring or other material.
A crawl space combustion air installation consists of a straight pipe from the PVC coupling on the burner box that extends into the crawl space and terminates with a 1/4” (6.4 mm) mesh screen and no elbows.
Combustion Air Source from Outdoors
1.Two permanent openings, one within 12” (30.5 cm) of the top and one within 12” (30.5 cm) of bottom of the confined space, Two per- manent openings, shall communicate directly or by means of ducts with the outdoors, crawl spaces or attic spaces.
2.One permanent openings, commencing within 12” (30.5 cm) of the top of the enclosure shall be permitted where the equipment has clearances of at least 1” (2.54 cm) from the sides and back and 6” (15.2 cm) from the front of the appliance. The opening shall com- municate directly with the outdoors and shall have a minimum free area of:
a.1 square inch per 3000 BTU per hour (322 cm2 per 0.879 kW) of the total input rating of all equipment located in the enclosure.
b.Not less than the sum of all vent connectors in the confined space.
3.The duct shall be least the same
4.The blocking effects of louvers, grilles and screens must be given consideration in calculating free area. If the free area of a specific louver or grille is not known. Refer to Table 11.
12” minimum between bottom of air intake and any material below.
12” Min.
FIGURE 40: Attic and Crawl Space Combustion Air Termination
28 | Johnson Controls Unitary Products |
