INSTALLATION INSTRUCTIONS Gas Furnace: (F/G)9MAE
40 440 01 4300 02
Specifications subject to change without notice.
Size the Vent and Combustion Air Pipes
General
Vent or Combustion Air
Pipe Diameters
Approved 2−pipe
termination fittings
2−in. 3−in. 4−in.
1 1/2−in. X N/A N/A
2−in. X N/A N/A
2 1/2−in. N/A X N/A
3−in. N/A X N/A
4−in. N/A X X
Note: Optional accessory 2−pipe termination brackets are
sized for 2−in. and 3−in. Pipe. If a termination bracket is
required for a 4−in. Termination, field fabricate the necessary
brackets and clamps.
Furnace combustion air and vent pipe connections are sized
for 2-in. (50 mm ND) PVC/ABS DWV pipe. The combustion air
and vent pipe connections also accommodate 60mm
polypropylene venting systems with outside diameters of
approximately 60 mm (2−3/8 inches). Any pipe diameter
change should be made outside furnace casing in vertical pipe.
Any change in diameter to the pipe must be made as close to
the furnace as reasonably possible (see Figure 48).
The Maximum Vent Length for the vent pipe and combustion air
pipe equals the Maximum Equivalent Vent Length (MEVL) in
Table 14 or Table 16, minus the number of fittings multiplied by
the deduction for each type of fitting used from Table 15.
Figure 48
Combustion−Air and Vent Pipe
Diameter Transition Location and
Elbow Configuration
A93034
FURNACE
NOT IN
HORIZONTAL
SECTION
PIPE DIAMENTER
TRANSITION IN
SECTION
NOTICE
Optional Configuration for Combustion Air Inlet
Pipe
In applications where there is a risk of excessive moisture
entering the combustion air inlet pipe, a moisture trap may be
added to the inlet pipe to help prevent moisture from entering
the furnace from the combustion air inlet pipe. See
Figure 49.
When sizing venting systems, the equivalent length of the
optional moisture trap (15 feet/5 M) must be taken into ac-
count
Optional Combustion Air Inlet
Moisture Trap
As an option to prevent moisture from trickling into the furnace
vestibule, a trap can be installed in the intake air pipe near the
furnace. Connecting a drain line to the trap is optional as trace
amounts of moisture will evaporate into the intake air stream. If
the combustion air inlet is located near a moisture exhaust
duct, or there are other concerns of excessive moisture being
drawn into the combustion air inlet, it is encouraged to connect
a drain line to the trap.
The trap can be constructed from a running tee of the same
diameter of the intake air pipe with EITHER a removable cap
attached to a 6-inch long pipe connected to the tee or the
External vent Trap Kit to help prevent contaminants from
entering the furnace. See Figure 49.
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