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equipped with means to prevent operation of either unit unless
the damper is in the full--heat or full--cool position.
AIR FOR COMBUSTION AND
VENTILATION
Provisions for adequate combustion, ventilation, and dilution air
must be provided in accordance with:
U.S. installations: Section 9.3 of the NFPA 54 /A ANSI
Z223.1--2006, Air for Combustion and Ventilation, and
applicable provisions of the local building codes.
Canadian installations: Part 8 of the CAN/CSA--B149.1--05,
Venting Systems and Air Supply for Appliances and all
authorities having jurisdiction.
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.
CAUTION
!
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.
Make--up air MUST be provided for the ventilation devices,
in addition to that required by the furnace. Refer to Carbon
Monoxide Poisoning Hazard warning in venting section of
these instructions to determine if an adequate amount of
make--up air is available.
!
WARNING
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.
S Spaces having less than 50 cubic feet per 1,000 Btuh require the
Outdoor Combustion Air Method.
S Spaces 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.
a. 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.
b. Size openings and ducts per Fig. 7 and Table 2.
c. TWOHORIZONTAL DUCTSrequire1 --in
2
of freearea
per 2,000 Btuh (1,100 mm
2
/kW) of combined input for
all gas appliances in the space per Fig. 7 and Table 2.
d. TWO OPENINGS OR VERTICAL DUCTS require 1
-- i n
2
of freearea per 4,000 Btuh (550 mm
2
/kW) for com-
bined input of all gas appliances in the space per Fig. 7
and Table 2.
3. ONE OUTDOOR OPENING requires:
a. One square inch of free area per 3,000 Btuh (734
mm
2
/kW) for combined input ofall 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
FURNACE
INPUT
(BTUH)
TWO HORIZONTAL DUCTS SINGLE DUCT OR OPENING TWO OPENINGS OR VERTICAL DUCTS
(1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/K W) (1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW) (1 SQ. IN./4,000 BTUH) (550 SQ. MM/K W)
Free Area of Opening
and Duct
Sq. In. (Sq. mm)
Round Duct
Dia.
In. (mm)
Free Area of Opening
and Duct
Sq. In. (Sq. mm)
Round Duct
Dia.
In. (mm)
Free Area of Opening
and Duct
Sq. In. (Sq. mm)
Round Duct
Dia.
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
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
58CT