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| Table 9: Free Area |
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| Minimum Free Area Required for Each Opening | |||
When a Category I furnace is removed or replaced, the original |
| BTUH Input | Horizontal Duct | Vertical Duct or | Round Duct | ||||
| Rating | Opening to Outside | |||||||
venting system may no longer be correctly sized to properly vent |
| (2,000 BTUH) | (4,000 BTUH) | ||||||
the attached appliances. |
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An improperly sized vent system can cause CARBON MONOXIDE | 40,000 | 20 in2 (129 cm2) | 10 in2 (64 cm2) | 4” (10 cm) | |||||
to spill into the living space causing personal injury, and or death. |
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60,000 | 30 in2 (193 cm2) | 15 in2 (97 cm2) | 5” (13 cm) | ||||||
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Table 8: Unconfined Space Minimum Area |
| 80,000 |
| 40 in2 (258 cm2) | 20 in2 (129 cm2) |
| 5” (13 cm) | |||
BTUH Input Rating |
| Minimum Free Area |
| 100,000 |
| 50 in2 (322 cm2) | 25 in2 (161 cm2) |
| 6” (15 cm) | |
Required for Each Opening |
| 120,000 |
| 60 in2 (387 cm2) | 30 in2 (193 cm2) |
| 7” (18 cm) | |||
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40,000 |
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| 40 in2 (258 cm2) |
| 130,000 |
| 65 in2 (419 cm2) | 33 in2 (213 cm2) |
| 7” (18 cm) |
60,000 |
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| 60 in2 (387 cm2) |
| EXAMPLE: Determining Free Area. |
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80,000 |
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| 80 in2 (516 cm2) |
| Appliance | 1 Appliance | 2 Total Input |
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100,000 |
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| 100 in2 (645 cm2) |
| 100,000 | + 30,000 = (130,000 ÷ 4,000) = 32.5 Sq. In. Vertical | ||||
120,000 |
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| 120 in2 (742 cm2) |
| Appliance | 1 Appliance | 2 Total Input |
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| 100,000 | + 30,000 = (130,000 ÷ 2,000) = 65 Sq. In. Horizontal | ||||||
130,000 |
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| 130 in2 (838 cm2) |
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| Gas |
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| Gas |
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| Gas |
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| Vent |
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Gable |
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| Vent |
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Vent |
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| Ventilated |
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| Attic |
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Optional |
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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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| Outlet |
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| Vent |
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| Air (b) |
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| Gas | Furnace |
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| Water |
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FIGURE 24: Outside and Ambient Combustion Air
Air Supply Openings and Ducts
1.An opening may be used in lieu of a duct 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 “COMBUSTION 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 in (30.5 cm) above, and within 24 in (61 cm) horizontally from, the burner level of the appliance having 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 in (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.
Combustion Air Source from Outdoors
1.Two permanent openings, one within 12 in (30.5 mm) of the top and one within 12 in (30.5 mm) of bottom of the confined space, Two permanent openings, shall communicate directly or by means of ducts with the outdoors, crawl spaces or attic spaces.
2.One permanent openings, commencing within 12 in (30.5 mm) of the top of the enclosure shall be permitted where the equipment has clearances of at least 1 in (2.54 cm) from the sides and back and 6 in (15.24 cm) from the front of the appliance. The opening shall communicate directly with the outdoors and shall have a min- imum free area of:
a.1 square in per 3000 Btu per hour (6.45 cm3 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 7 to estimate free area.
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.
Vent and Supply (Outside) Air Safety Check Procedure
For Category I furnaces, vent installations shall be in accordance with Parts 7 and 11 of the National Fuel Gas Code, ANSI Z223.1/NFPA 54, and or Section 7 and Appendix B of the CSA B149.1, Natural Gas and Propane Installation Codes, the local building codes, furnace and vent manufacture's instructions.
18 | Johnson Controls Unitary Products |
