This type of installation requires that the supply air to the appliance(s) be of a sufficient amount to support all of the appliance(s) in the area. Operation of a mechanical exhaust, such as an exhaust fan, kitchen ventilation system, clothes dryer or fireplace may create conditions requiring special attention to avoid unsatisfactory operation of gas appliances. A venting problem or a lack of supply air will result in a hazardous condition, which can cause the appliance to soot and gen- erate dangerous levels of CARBON MONOXIDE, which can lead to serious injury, property damage and / or death.
An unconfined space is not less than 50 cu.ft (1.42 m3) per 1,000 Btu/ hr (0.2928 kW) input rating for all of the appliances installed in that area.
Rooms communicating directly with the space containing the appli- ances are considered part of the unconfined space, if doors are fur- nished with openings or louvers.
A confined space is an area with less than 50 cu.ft (1.42 m3) per 1,000 Btu/hr (0.2928 kW) input rating for all of the appliances installed in that area. The following must be considered to obtain proper air for combus- tion and ventilation in confined spaces.
Combustion Air Source From Outdoors
The blocking effects of louvers, grilles and screens must be given con- sideration in calculating free area. If the free area of a specific louver or grille is not known, refer to Table 12, to estimate free area.
Table 12: Estimated Free Area |
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Wood or Metal | Wood | |
Louvers or Grilles | Metal | |
Screens+ | 1/4” (6.4 mm) | |
mesh or larger 100% | ||
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* Do not use less than 1/4” (6.4 mm) mesh
+Free area of louvers and grille varies widely; the installer should follow louver or grille manufacturer’s instructions.
Dampers, Louvers and Grilles (Canada Only)
1.The free area of a supply air opening shall be calculated by sub- tracting the blockage area of all fixed louvers grilles or screens from the gross area of the opening.
2.Apertures in a fixed louver, a grille, or screen shall have no dimen- sion smaller than 1/4” (6.4 mm).
3.A manually operated damper or manually adjustable louvers are not permitted for use.
4.A automatically operated damper or automatically adjustable lou- vers shall be interlocked so that the main burner cannot operate unless either the damper or the louver is in the fully open position.
When a Category I furnace is removed or replaced, the original vent- ing system may no longer be correctly sized to properly vent the attached appliances.
An improperly sized vent system can cause CARBON MONOXIDE to spill into the living space causing personal injury, and or death.
Table 13: Unconfined Space Minimum Area
| BTUH Input Rating | Minimum Free Area Required for Each Opening | ||||
| 40,000 |
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| 40 in2 (258 cm2) |
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| 60,000 |
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| 60 in2 (387 cm2) |
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| 80,000 |
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| 80 in2 (516 cm2) |
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| 100,000 |
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| 100 in2 (645 cm2) |
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| 120,000 |
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| 120 in2 (742 cm2) |
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Table 14: Free Area |
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| Minimum Free Area Required for Each Opening | |||
| BTUH Input |
| Horizontal Duct | Vertical Duct or | Round Duct | |
| Rating |
| Opening to Outside | |||
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| (2,000 BTUH) | (4,000 BTUH) | |||
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| (4,000 BTUH) |
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| 40,000 |
| 20 in2 (129 cm2) | 10in2 (64cm2) | 4” (10 cm) | |
| 60,000 |
| 30 in2 (193 cm2) | 15 in2 (97 cm2) | 5” (13 cm) | |
| 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) | |
| 120,000 |
| 60 in2 (387 cm2) | 30 in2 (193 cm2) | 7” (18 cm) | |
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| EXAMPLE: Determining Free Area. |
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| Appliance 1 Appliance 2 Total Input |
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| 100,000 +30,000 = (130,000 ÷ 4,000) = 32.5 Sq. In. Vertical | |||||
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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 | |||||
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| Gas |
Gable |
| Vent |
Vent | Ventilated |
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Optional | Attic |
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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) | rnaceuF |
| Gas | |
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| Water |
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| Heater |
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| Ventilated |
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| Crawl Space |
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| Gas |
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| Gable | Vent |
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| Vent |
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| Ventilated |
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| Attic |
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| Top Above |
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| Insulation |
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Soffit |
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| Outlet |
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Vent |
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| Air (b) |
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| Heater | Furnace | Inlet | Inlet | Heater |
| Gas |
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| Gas |
Inlet | Water |
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| Water |
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Air (b) |
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| Air (a) | Air (b) |
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Gas
Vent
| Outlet |
| Air (a) |
Furnace | Inlet |
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| Air (a) |
FIGURE 38: 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 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).
28 | Johnson Controls Unitary Products |
