312AAV
!CAUTION
FURNACE CORROSION HAZARD
Failure to follow this caution may result in furnace damage.
Air for combustion must not be contaminated by halogen compounds, which include fluoride, chloride, bromide, and iodide. These elements can corrode heat exchangers and shorten furnace life. Air contaminants are found in aerosol sprays, detergents, bleaches, cleaning solvents, salts, air fresheners, and other household products.
!WARNING
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal injury or death.
The operation of exhaust fans, kitchen ventilation fans, clothes dryers, attic exhaust fans or fireplaces could create a NEGATIVE PRESSURE CONDITION at the furnace.
The requirements for combustion and ventilation air depend upon whether or not the furnace is located in a space having a volume of at least 50 cubic feet per 1,000 Btuh input rating for all gas appliances installed in the space.
SSpaces having less than 50 cubic feet per 1,000 Btuh require the Outdoor Combustion Air Method.
SSpaces having at least 50 cubic feet per 1,000 Btuh may use the Indoor Combustion Air, Standard or Known Air Infiltration Method.
Outdoor Combustion Air Method
1.Provide the space with sufficient air for proper combus- tion, ventilation, and dilution of flue gases using perman- ent horizontal or vertical duct(s) or opening(s) directly communicating with the outdoors or spaces that freely communicate with the outdoors.
2.Fig. 7 illustrates how to provide TWO OUTDOOR OPENINGS, one inlet and one outlet combustion and ventilation air opening, to the outdoors.
e.One opening MUST commence within 12 in. (300 mm) of the ceiling and the second opening MUST commence within 12 in. (300 mm) of the floor.
f.Size openings and ducts per Fig. 7 and Table 2.
g.TWO HORIZONTAL DUCTS require 1
h.TWO OPENINGS OR VERTICAL DUCTS require 1
3.ONE OUTDOOR OPENING requires:
a.One square inch of free area per 3,000 Btuh (734 mm2/kW) for combined input of all gas appliances in the space per Table 2 and
b.Not less than the sum of the areas of all vent connectors in the space.
Table 2 – Minimum Free Area Required for Each Combustion Air opening of Duct to Outdoors
| TWO HORIZONTAL DUCTS | SINGLE DUCT OR OPENING | TWO OPENINGS OR VERTICAL DUCTS | |||
FURNACE | (1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/KW) | (1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW) | (1 SQ. IN./4,000 BTUH) (550 SQ. MM/KW) | |||
INPUT |
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Free Area of Opening | Round Duct | Free Area of Opening | Round Duct | Free Area of Opening | Round Duct | |
(BTUH) | and Duct | Dia. | and Duct | Dia. | and Duct | Dia. |
| Sq. In. (Sq. mm) | In. (mm) | Sq. In. (Sq. mm) | In. (mm) | Sq. In. (Sq. mm) | In. (mm) |
44,000 | 22 (14194) | 6 (152) | 14.7 (9484) | 5 (127) | 11 (7096) | 4 (102) |
66,000 | 33 (21290) | 7 (178) | 22 (14193) | 6 (152) | 16.5 (10645) | 5 (127) |
88,000 | 44 (28387) | 8 (203) | 29.3 (18903) | 7 (178) | 22 (14193) | 6 (152) |
110,000 | 55 (35484) | 9 (229) | 36.7 (23677) | 7 (178) | 27.5 (17742) | 6 (152) |
132,000 | 66 (42580) | 10 (254) | 44 (28387) | 8 (203) | 33 (21290) | 7 (178) |
154,000 | 77 (49677) | 10 (254) | 51.3 (33096) | 9 (229) | 38.5 (24839) | 8 (203) |
EXAMPLES: Determining Free Area
FURNACE |
| WATER HEATER |
| TOTAL INPUT |
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110,000 | + | 30,000 | = (140,000 divided by 4,000) | = | 35.0 | Sq. In. for each two Vertical Ducts or Openings | |
66,000 | + | 40,000 | = | (106,000 divided by 3,000) | = | 35.3 | Sq. In. for a Single Duct or Opening |
88,000 | + | 30,000 | = | (118,000 divided by 2,000) | = | 59.0 | Sq. In. for each of two Horizontal Ducts |
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