Outside air openings shall directly communicate with the outdoors. When combustion air is drawn from the outside through a duct, the net free area of each of the two openings must have twice (2 times) the free area required for Outside Air/2 Openings. Table A lists the requirements for the appliance only, additional gas fired appliances located in the same room will require an increase in the net free area to supply adequate combustion air for all appliances. Combustion air requirements are based on the latest edition of the National Fuel Gas Code, ANSI Z223.1, in Canada refer to National Standard CAN B149.1 or B149.2. Check all local code requirements for combustion air.
All dimensions are 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 room where the appliance is installed. Each opening must have a net free area as specified in Table A. Single openings shall be located within 12" (30 cm) of the ceiling.
CAUTION
Under no circumstances should the room where the appliance is installed ever be under a 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 appliance.
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, tricholorethylene, perchlorethylene, chlorine, etc. These chemicals, when burned, form acids which quickly attack the heat exchanger finned tubes, headers, flue collectors, and the vent system. The result is improper combustion and a
TABLE - A
MINIMUM RECOMMENDED COMBUSTION AIR SUPPLY
|
| Combustion Air Source |
| |
| Input | Outside Air/2 | Outside Air/1 | Inside Air/2 |
| Btu/hr | Openings | Opening | Openings |
|
|
|
|
|
45,000 | 12 in2 | 15 in2 | 100 in2 | |
75,000 | 19 in2 | 25 in2 | 100 in2 | |
90,000 | 23 in2 | 30 in2 | 100 in2 | |
135,000 | 34 in2 | 45 in2 | 135 in2 | |
180,000 | 45 in2 | 60 in2 | 180 in2 | |
199,999 | 50 in2 | 67 in2 | 200 in2 | |
215,000 | 55 in2 | 74 in2 | 224 in2 | |
225,000 | 56 in2 | 75 in2 | 225 in2 | |
260,000 | 67 in2 | 89 in2 | 269 in2 | |
270,000 | 68 in2 | 90 in2 | 270 in2 | |
315,000 | 79 in2 | 105 in2 | 315 in2 | |
360,000 | 90 in2 | 120 in2 | 360 in2 | |
|
|
|
| |
399,999 | 100 in2 | 133 in2 | 400 in2 | |
|
|
|
| |
500,000 | 125 in2 | 167 in2 | 500 in2 | |
|
|
|
|
|
6
