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Regardless of the diameter of pipe used, the standard roof
and wall terminations described in section Exhaust Piping
Terminations should be used. Exhaust vent termination
pipe is sized to optimize the velocity of the exhaust gas as
it exits the termination. Refer to TABLE 10.
In some applications which permit the use of several dif-
ferent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox’ Application Department for assis-
tance in sizing vent pipe in these applications.
TABLE 7
MINIMUM VENT PIPE LENGTHS
SLP99DF
Model
Min. Equiv.
Vent Lenght
Example
070
15 ft.*
5 ft. plus 2 elbows of 1-1/2”,
2”, 2-1/2” or 3” diameter pipe
090,110
5 ft. plus 2 elbows of 2”,
2-1/2” or 3” diameter pipe
*Any approved termination may be added to the minimum equiv-
alent length listed. Two 45 degree elbows are the equivalent to
one 90 degree elbow.
NOTE - It is acceptable to use any pipe size which ts
within the guidelines allowed in TABLE 8.
NOTE - The exhaust collar on all models is sized to ac-
commodate 2” Schedule 40 vent pipe. Contact the Appli-
cation Department for more information concerning sizing
of vent systems which include multiple pipe sizes.
NOTE - If right side venting option is used, you must in-
clude the elbow at the furnace in the elbow count. If tran-
sitioning to 3” dia pipe, this elbow equates to 20’ of equiv-
alent vent length for all models.
NOTE - All horizontal runs of exhaust pipe must slope
back toward unit. A minimum of 1/4” (6mm) drop for each
12” (305mm) of horizontal run is mandatory for drainage.
NOTE - Exhaust pipe MUST be glued to furnace exhaust
ttings.
NOTE - Exhaust piping should be checked carefully to
make sure there are no sags or low spots.
Use the following steps to correctly size vent pipe diam-
eter.
IMPORTANT
Do not use screens or perforated metal in exhaust
or intake terminations. Doing so will cause freeze-
ups and may block the terminations.
Piping Size Process
1
2
3
4
5
6
Which style termination
being used?
Standard or
concentric?.
Which needs
most elbows?
Intake or
exhaust?
How many elbows?
Count all elbows inside
and outside house.
Desired pipe size?
Find max intake or
exhaust pipe length.
Includes all vent pipe and
elbows inside and outside
the house.
What is the altitude of
the furnace installation?
7
What is the
furnace capacity?
FIGURE 20
NOTE - Lennox oers a glueless vent adapter kit 17H92
as an option for exhaust exiting at the furnace top cap
coupling.
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