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FURNACE
NOT IN
HORIZONTAL
SECTION
Fig. 38 - - Combustion Air and Vent Pipe Transition
Location and Elbow Configuration
CAUTION
!
UNIT OPERATION HAZARD
Failure to follow this caution may result in intermittent unit
operation.
When installing combustion air and vent system of short
pipe length, the smallest allowable pipe diameter must be
used.
CAUTION
!
UNIT CORROSION HAZARD
Failure to follow this caution may result in unit component
damage.
Excessive exposure to contaminated combustion air may
result in safety and performance related problems.
Combustion air must not be taken from inside structure
because that air is frequently contaminated by halogens,
which include fluorides, chlorides, bromides, and iodides.
These elements are found in aerosols, detergents, bleaches,
cleaning solvents, salts, air fresheners, adhesives, paint, and
other household products. Locate combustion- -air inlet as
far as possible from swimming pool and swimming pool
pump house.
EXAMPLE: This 80,000 BTUH furnace located in Indianapolis,
elevation 650 ft. (198.1M) above sea level, could be installed as a
direct Vent / 2- -pipe system that requires 3 elbows and 17 ft.
(5.1M) of vent pipe, along with 5 elbows and 16 ft. (4.8M) of
combustion- -air pipe. Table 7 indicates this application would
allow a 1- -1/2- -in. diameter vent pipe, but require a 2- -in. diameter
combustion air pipe. According to Table 7, 1- -1/2- -in. diameter
pipe is good for 20 ft. (6.0M) with 3 elbows, but only 10 ft.
(3.0M) with 5 elbows. Therefore, 2- -in. diameter pipe must be
used for both vent and combustion- -air pipes since the largest
required diameter must always be used for both pipes. If the same
installation was made in Albuquerque, elevation 5250 ft.
(1600.2M) above sea level, installation would require 2- - in.
diameter vent pipe and combustion- -air pipe. At 5001 to 6000- -ft
(1524M - - 1828M) elevation, 1- -1/2- -in. pipe is not allowed with
5 elbows, but 2- -in. pipe is good for 68 ft. (20.7M) with 5 elbows
are required.
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
A93034
COMBUSTION AIR PIPE
General
Furnace combustion- -air connection must be attached as shown in
Fig. 39. Combustion- -air intake housing plug may need to be
relocated in some applications.
NOTE:
Select 1 vent pipe connection and
1 combustion-air pipe connection.
AIR
FLOW
COMBUSTION-
COMBUSTION-
AIR
AIR
VENT
VENT
UPFLOW
COMBUSTION-
AIR
VENT
AIR
FLOW
HORIZONTAL-LEFT DISCHARGE
Fig. 39 - - Combustion Air and Vent Pipe Connections
NOTE: All pipe joints must be cemented except attachment of
combustion- -air pipe to inlet housing connection, since it may be
necessary to remove pipe for servicing.
NOTE: A 2- -in. diameter pipe must be used within the furnace
casing. Make all pipe diameter transitions outside furnace casing.
Attachment of Combustion Air Pipe
NOTE: Combustion air pipe system has the same diameter and
same length as the vent pipe as mentioned in section
"Combustion- - - -Air and Vent Pipe Diameter."
1. Determine location of combustion- -air intake pipe connec-
tion to combustion- -air intake housing as shown in Fig. 39
for application.
2. Verify combustion- -air intake housing plug fitting is in-
stalled in appropriate unused intake housing connection.
3. Install combustion- -air pipe grommet (factory- -supplied in
loose parts bag) into selected furnace casing combustion
air pipe hole.
4. Determine the number of combustion air disk halves to be
installed in the combustion air intake housing. Insert per-
forated disk half or assembly (factory supplied in loose
parts bag) in intake housing where combustion- -air intake
pipe will be connected.
5. Insert assembled combustion air inlet pipe into intake
housing as shown in Fig. 39.
NOTE: Do not cement combustion air intake pipe permanently
to combustion air intake housing since it may be necessary to
remove pipe for service of igniter or flame sensor.
6. Drill a 1/8- -in. hole in 2- -in, combustion air pipe using the
hole in intake housing as a guide.
7. Install a field- -supplied No. 6 or No. 8 sheet metal screw
into combustion air pipe.
34
NOTE:
Select 1 vent pipe connection and
1 combustion-air pipe connection.
VENT
VENT
COMBUSTION-
COMBUSTION-
AIR
AIR
AIR
FLOW
DOWNFLOW
COMBUSTION-
AIR
VENT
AIR
FLOW
HORIZONTAL-RIGHT DISCHARGE
A96187
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