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| Table 14: Free Area |
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| Minimum Free Area Required for Each Opening | |||
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When a Category I furnace is removed or replaced, the original |
| BTUH Input |
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| Horizontal Duct | Vertical Duct or | Round Duct | |||||||
venting system may no longer be correctly sized to properly vent |
| Rating | Opening to Outside | |||||||
the attached appliances. |
| (2,000 BTUH) | (4,000 BTUH) | |||||||
An improperly sized vent system can cause CARBON MONOXIDE |
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| (4,000 BTUH) |
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60,000 | 30 in2 (193 cm2) | 15 in2 (97 cm2) | 5” (13 cm) | |||||||
to spill into the living space causing personal injury, and or death. | ||||||||||
Table 13: Unconfined Space Minimum Area in Square Inch |
| 80,000 | 40 in2 (258 cm2) | 20 in2 (129 cm2) |
| 5” (13 cm) | ||||
| 100,000 | 50 in2 (322 cm2) | 25 in2 (161 cm2) |
| 6” (15 cm) | |||||
BTUH Input Rating | Minimum Free Area in Square Inches | 120,000 | 60 in2 (387 cm2) | 30 in2 (193 cm2) |
| 7” (18 cm) | ||||
Required for Each Opening |
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| EXAMPLE: Determining Free Area. |
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60,000 |
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| 60 (387 cm2) |
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| Appliance 1 Appliance 2 Total Input |
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80,000 |
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| 80 (516 cm2) |
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| 100,000 +30,000 = (130,000 ÷ 4,000) = 32.5 Sq. In. Vertical | ||||
100,000 |
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| 100 (645 cm2) |
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| Appliance 1 Appliance 2 Total Input |
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| 100,000 +30,000 = (130,000 ÷ 2,000) = 65 Sq. In. Horizontal | ||||||
120,000 |
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| 120 (742 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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| Vent |
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| Ventilated |
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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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| Insulation |
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Soffit | Outlet |
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Vent | Air (a) |
| Soffit |
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| Outlet |
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| Outlet |
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| Vent |
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| Air (b) |
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| Air (a) |
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| Gas | Furnace |
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| Water |
| Gas | Furnace |
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| Heater |
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| Inlet | Inlet | Heater | Inlet | |||||
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| Air (a) | Air (b) |
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| Crawl Space |
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FIGURE 37: 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 appli- ance. 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 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” (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” (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 in. per 3000 Btu per hour (6.45 cm3 per 0.879 kW) of the total input rating of all equipment located in the enclo- sure.
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 12.
Johnson Controls Unitary Products | 27 |
