VENT PIPE
NOTE:
Furnace vent pipe connections are sized for 2-in. pipe.
Any vent pipe size change should be made outside furnace casing
in vertical pipe. (See Fig. 37.) This allows proper drainage of vent
condensate.
Determine vent pipe diameter and maximum pipe lengths using
Table 6.
Furnace vent pipe connection must be attached as shown in Fig.
34. Inducer housing alternate vent cap may need to be relocated in
some applications.
NOTE:
Starting at furnace, slope vent pipe a minimum of 1/4 in.
per linear ft upward to termination(s) with no sags between
hangers.
When vent pipe is exposed to temperatures below freezing,
such as when it passes through an unheated space or when a
chimney is used as a raceway, pipe must be insulated as
described in Table 7 with Armaflex-type insulation. Failure to
follow this caution will result in minor unit operation.
An abandoned masonry chimney may be used as a raceway for
properly insulated and supported vent pipe. Each furnace must
have its own vent pipe and be terminated individually, as shown in
Fig. 41.
Other gas appliances with their own venting system may also use
the abandoned chimney as a raceway providing it is permitted by
local code, the current edition of the National Fuel Gas Code and
the vent or liner manufacturer’s installation instructions. Care must
be taken to prevent the exhaust gases from one appliance from
contaminating the combustion air of other gas appliances.
Vent pipes must be airtight and watertight. Failure to follow
this warning could result in property damage, personal injury,
or death.
NOTE:
The minimum vent pipe length for these furnaces is 5 ft.
Short pipe lengths (5-8 ft) may discharge water droplets. These
droplets may be undesirable, and a 12-in. minimum offset pipe
section is recommended to reduce excessive droplets from exiting
vent pipe outlet. (See Fig. 38.)
NOTE:
Do not count elbows or pipe sections in terminations or
within furnace. See shaded areas in Fig. 40.
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. Table 6 indicates
this application would allow a 2-in. diameter vent pipe. At
0-2000 ft elevation, 2-in. pipe is good for up to 35 ft with
3 elbows. If same installation were in Albuquerque, eleva-
tion 5250 ft above sea level, installation would require 2-1/2
in. vent pipe. At 5001- to 6000-ft elevation, 2-in. pipe is
allowed for up to 23 ft with 3 elbows, but 2-1/2 in. pipe can
be used for up to 70 ft with 3 elbows.
Install vent pipe as follows:
1. Determine location of vent pipe connection to inducer housing
as shown in Fig. 34 for application.
2. Reposition elastomeric (rubber) inducer housing outlet cap
and clamp to appropriate unused inducer housing connection.
Tighten clamp.
Inducer housing outlet cap must be installed and fully seated
against inducer housing. Clamp must be tightened to prevent
any condensate leakage. Failure to follow this warning could
result in electrical shock, fire, personal injury, or death.
3. Install pipe support (factory-supplied in loose parts bag) into
selected furnace casing vent pipe hole. Pipe support should be
positioned at bottom of casing hole.
Vent pipe must be installed and fully seated against inducer
housing internal stop. Clamp must be tightened to prevent any
condensate leakage. Failure to follow this warning could
result in electrical shock, fire, personal injury, or death.
NOTE:
A 2-in. diameter pipe must be used within the furnace
casing. Make all pipe diameter transitions outside furnace casing.
4. Be certain that mating surfaces of inducer housing connection
elastomeric coupling, and 2-in. diameter vent pipe are clean
and dry. Assemble the elastomeric (rubber) vent coupling
(with 2 loose clamps) onto inducer housing connection. Insert
the 2-in. diameter vent pipe through the elastomeric (rubber)
coupling and fully into inducer housing connection until it
bottoms on the internal stop. Tighten both clamps to secure the
pipe to inducer housing. Tighten the clamp screws to 15 in.-lb.
of torque.
5. Install casing hole filler cap (factory-supplied in loose parts
bag) in unused vent pipe casing hole.
VENT EXTENSION PIPE
Some furnaces are supplied with a PVC vent extension pipe
(2-in. diameter by 12-in. long). This pipe has a built-in
channel to assist vent condensate disposal. When this vent
extension pipe is supplied, it must be used to connect the field
vent pipe to furnace inducer housing on ALL upflow and
downflow applications.
NOTE:
See label on vent extension pipe for proper installation.
This pipe may be shortened if an elbow is used to connect vent
extension tube to field-installed vent pipe.
6. Working from furnace to outside, cut pipe to required
length(s).
7. Deburr inside and outside of pipe.
Fig. 37—Vent Pipe Diameter Transition Location
and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
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