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COMBUSTION
AIR PIPE
BURNER
BOX
COMBUSTION AIR
INTAKE HOUSING
3/8" ID TUBE
TRAP
TO OPEN
DRAIN
3/16"
DRILL
4″
MIN
A93035
Fig. 40 -- Intake Housing Plug Fitting Drain
8. Install casing hole filler cap (factory--supplied in loose
parts bag) in unused combustion air pipe casing hole.
Attachment of Combustion Air Intake Housing Plug
Fitting
The combustion--air intake plug fitting must be installed in
unused combustion air intake housing. This fitting must be
attached by using R TV sealant, or by drilling a 1/8--in. hole in
fitting, using hole in intake housing as a guide. Install a
field--supplied No. 6 or No. 8 sheet metal screw.
NOTE: DO NOT OVERTIGHTEN SCREW. Breakage of
intake housing or fitting may cause air leakage to occur.
A plugged drain connection has been provided on this fitting for
use when moisture is found in combustion air intake pipe and
combustion box.
If use of this drain connection is desired, drill out fitting’ s tap
plug with 3/16--in. drill and connect a field--supplied 3/8--in. tube.
This tube should be routed to open condensate drain for furnace
and A/C (if used), and should be trapped, as shown in Fig. 40.
NOTE: (Direct Vent/2--Pipe Sy stem ONLY). Moisture in
combustion air intake may be a result of improper termination.
Ensure combustion air pipe termination is similar to those as
shown in Fig. 36 so that i t will not be susceptible to area where
light snow or others sources of moisture could be pulled in.
Combustion Air Termination -- Ventilated Combustion
Air
Option
Provisions for adequate combustion, ventilation, and dilution a ir
must be provided in accordance with:
S U.S. Installations: Section 9.3 of the NFGC, Air f or
Combustion and Ventilation and applicable provisions
of the local building codes.
S Canadian Installations: Part 8 of CAN/CS--B149.1--05.
Venting Systems and Air Supply for Appliances and all
authorities having jurisdiction.
Combustion air is piped directly to the burner box on furnace
using t he same materials used to vent the furnace. (See Table 5.)
The c ombustion air pipe is terminated in an attic or crawl space
that is well ventilated with OUTDOOR AIR and is well isolated
from the living space or garage. If the furnace is installed in a well
ventilated attic, crawlspace or other enclosure, the combustion air
pipe can be terminated in the same space.
UNIT CORROSION HAZARD
Failure to follow this caution may result in reduced furnace
component life.
Air for combustion must not be contaminated by halogen
compounds, which include fluoride, chloride, bromide, and
iodide. These elements may corrode heat exchangers and
shorten furnace life. Air contaminants are found in aerosol
sprays, deter gents, bleaches, cleaning solvents, salts, air
fresheners, and other household products.
CAUTION
!
The combustion air pipe cannot be terminated in attics or
crawlspaces that use ventilation fans designed to operate during
the heating season. If ventilation f ans a re present in these areas,
the combustion air pipe must terminate outdoors as a Direct
Vent/2-- Pipe system.
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.
Makeup air MUST be provided for the ventilation devices,
in addition to that required by the furnace. Refer to the
Carbon Monoxide Poisoning Hazard warning at the end of
this section to determine if an adequate amount of make-- up
air is available.
!
WARNING
NOTE: Combustion air pipe must have the same diameter as
vent pipe.
An attic or crawlspace may be considered a space that freely
communicates with the outdoors provided there are adequate
permanent ventilation openings directly to outdoors having free
area of at least 1 --in.2/4,000 Btuh of total input rating for all gas
appliances in the space.
NOTE: In determining the free area of an opening, the blocking
effect of the louvers, grilles, and screens must be considered. If
the free area of a louver or grille design is unknown, it may be
assumed that wood louvers have a 20 percent free area, and metal
louvers or grilles have a 60 percent free area. Screens, when used,
must not be smaller than 1/4 --in. mesh. Louvers and grilles must
be constructed so they cannot be closed.
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal
injury or death.
Many homes require air to be supplied from outdoors for
furnace combustion, ventilation, and dilution of flue gases.
The furnace combustion air supply must be provided in
accordance with this instruction manual.
!
WARNING
Attic terminations require at least (1) 90 degree elbow, with the
open end pointing horizontally or downward. The open end of
the elbow must be at least 12--in. (304.8mm) above any
insulation or other materials. Screen the elbow with a wire mesh
screen no smaller than 3/8 --inch square. (See Fig. 41.)
355CAV