Carrier 58MCA Installation, Start-Up, And Operating Instructions Manual page 23

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. 27—Combustion-Air and Vent Pipe
Connections
to reduce excessive droplets from exiting vent pipe outlet.
COMBUSTION-AIR AND VENT PIPE DIAMETER
Determine combustion-air and vent pipe diameter.
1. Using Table 6, individually determine the combustion-air and
vent pipe diameters. Pick the larger of these 2 pipe diameters
and use this diameter for both combustion-air and vent pipes.
2. When installing vent systems of short pipe length, use the
smallest allowable pipe diameter. Do not use pipe size greater
than required or incomplete combustion, flame disturbance, or
flame sense lockout may occur.
NOTE: Do not count elbows or pipe sections in terminations or
within furnace. See shaded areas in Fig. 30, 31, 32, 33, and 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
EXAMPLE:
An 080-12 size furnace located in Indianapolis, elevation
650 ft above sea level, could be installed in an application
requiring 3 elbows and 32 ft of vent pipe, along with 5
elbows and 34 ft of combustion-air pipe. Table 6 indicates
this application would allow a 2-in. diameter vent pipe, but
require a 2-1/2 in. diameter combustion air pipe (2-in. pipe
is good for 35 ft with 3 elbows, but only 30 ft with 5
elbows). Therefore, 2-1/2 in. diameter pipe must be used
for both vent and combustion-air pipes since larger required
diameter must always be used for both pipes. If same
installation were in Albuquerque, elevation 5250 ft above
sea level, installation would require 2-1/2 in. vent pipe and
combustion-air pipe. At 5001- to 6000-ft elevation, 2-in.
pipe is only good for 17 ft with 5 elbows, and 2-1/2 in. pipe
is good for 70 ft with 5 elbows.
COMBUSTION-AIR AND VENT PIPE ATTACHMENT
NOTE: All pipe joints must be watertight except attachment of
combustion-air pipe to inlet housing connection, since it may be
necessary to remove pipe for servicing.
1. Attach combustion-air pipe as follows:
a. Determine location of combustion-air intake pipe connec-
tion to combustion-air intake housing as shown in Fig. 27
for application.
b. Reposition combustion-air intake housing plug fitting in
appropriate unused intake housing connection.
c. If required, insert perforated disk assembly (factory-
supplied in loose parts bag) in intake housing where
combustion-air intake pipe will be connected. If half disk
set is required, install with shoulder of disk against stop in
combustion-air inlet.
d. Install pipe support (factory-supplied in loose parts bag)
into selected furnace casing combustion-air pipe hole. Pipe
support should be positioned at bottom of casing hole.
e. Insert 2-in. diameter pipe into intake housing.
NOTE: A 2-in. diameter pipe must be used within the furnace
casing. Make all pipe diameter transitions outside furnace casing.
f. Drill a 1/8-in. hole in 2-in. combustion-air pipe using hole
in intake housing as a guide.
g. Install a field-supplied No. 6 or No. 8 sheet metal screw
into combustion-air pipe.
NOTE: DO NOT OVER TIGHTEN SCREW. Breakage to intake
housing or fitting may cause air leakage to occur.
NOTE: Do not attach combustion-air intake pipe permanently to
combustion-air intake housing since it may be necessary to remove
pipe for service of ignitor or flame sensor.
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 RTV 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 OVER TIGHTEN SCREW. Breakage to 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.
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