Installation & Operation Manual
1 Determine boiler location (continued)
4.If a single combustion air opening is provided to bring combustion air in directly from the outdoors, the opening must be sized based on a minimum free area of one square inch per 3000 Btu/hr (7 cm2 per kW). This opening must be located within 12” (30 cm) of the top of the enclosure (see FIG.
Combustion air requirements are based on the latest edition of the National Fuel Gas Code, NFPA 54 / ANSI Z223.1; in Canada refer to the latest edition of CGA Standard CAN/CSA B149.1. Check all local code requirements for combustion air. All dimensions based on net free area in square inches. Metal louvers or screens reduce the free area of a combustion air opening a minimum of approximately 25%. Check with louver manufacturers for exact net free area of louvers.
Where two openings are provided, one must be within 12" (30 cm) of the ceiling and one must be within 12" (30 cm) of the floor of the equipment room. Each opening must have a net free area as specified in Table 1B. Single openings shall commence within 12" (30 cm) of the ceiling. The minimum dimension of air openings shall not be less than 3" (80 mm).
CAUTION Under no circumstances should the equipment room ever be under negative
pressure. Particular care should be taken where exhaust fans, attic fans, clothes dryers, compressors, air handling units, etc., may take away air from the unit.
The combustion air supply must be completely free of any flammable vapors that may ignite or chemical fumes which may be corrosive to the appliance. Common corrosive chemical fumes which must be avoided are fluorocarbons and other halogenated compounds, most commonly present as refrigerants or solvents, such as Freon, trichlorethylene, perchlorethylene, chlorine, etc. These chemicals, when burned, form acids which quickly attack the stainless steel heat exchanger, headers, flue collectors, and the vent system.
The result is improper combustion and a
EXHAUST FANS: Any fan or equipment which exhausts air from the equipment room may deplete the combustion air supply and/or cause a downdraft in the venting system. Spillage of flue products from the venting system into an occupied living space can cause a very hazardous condition that must be corrected immediately.
TABLE - 1B
MINIMUM RECOMMENDED COMBUSTION
AIR SUPPLY TO EQUIPMENT ROOM
| FIG. | FIG. |
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| *Outside Air from | *Outside Air from |
| Inside Air from |
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| 2 Ducts Delivered from Interior Space2 | *Outside Air from | |||||||
Model | 2 Openings Directly from | 2 Ducts Delivered from |
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Number | Outdoors1 | Outdoors1 | Same Story | Different | 1 Opening Directly | ||||
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| Stories | from Outdoors, in |
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| Top | Bottom | Top | Bottom | Top |
| Bottom | Total | |
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| Opening, in2 | Opening, in2 | Opening, in2 | Opening, in2 | Opening, in2 |
| Opening, in2 | Opening, in2 |
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| (cm2) | (cm2) | (cm2) | (cm2) | (cm2) |
| (cm2) | (cm2) |
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FB 1500 | 375 | 375 | 750 | 750 | 1500 |
| 1500 | 3000 | 500 |
(2420) | (2420) | (4839) | (4839) | (9678) |
| (9678) | (19355) | (3226) | |
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FB 2000 | 500 | 500 | 1000 | 1000 | 2000 |
| 2000 | 4000 | 667 |
(3226) | (3226) | (6452) | (6452) | (12904) |
| (12904) | (25807) | (4304) | |
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FB 2500 | 625 | 625 | 1250 | 1250 | 2500 |
| 2500 | 5000 | 833 |
(4033) | (4033) | (8065) | (8065) | (16129) |
| (16129) | (32258) | (5381) | |
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FB 3000 | 750 | 750 | 1500 | 1500 | 3000 |
| 3000 | 6000 | 1000 |
(4839) | (4839) | (9678) | (9678) | (19355) |
| (19355) | (38710) | (6452) | |
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FB 3500 | 875 | 875 | 1750 | 1750 | 3500 |
| 3500 | 7000 | 1167 |
(5646) | (5646) | (11291) | (11291) | (22581) |
| (22581) | (45162) | (7530) | |
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The above requirements are for the appliance only; additional gas fired appliances in the equipment room will require an increase in the net free area and/or volume to supply adequate combustion air for all appliances.
No combustion air openings are needed when the appliance is installed in a space with a volume NO LESS than 50 cubic feet per 1,000 Btu/hr of all installed gas fired appliances. Buildings MUST NOT be of *“Tight Construction”3.
1Outside air openings shall directly communicate with the outdoors.
2Combined interior space must be 50 cubic feet per 1,000 Btu/hr input. Buildings MUST NOT be of *“Tight Construction”.
3”Tight Construction” is defined as a building with less than 0.40 ACH (air changes per hour). For buildings of “Tight Construction”, provide air openings into the building from outside.
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