Lennox SLP98DFV Installation Instructions Manual page 15

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 9.
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 6
MINIMUM VENT PIPE LENGTHS
SLP98DF Min. Equiv.
Model Vent Lenght
070, 090, 110 15 ft.*
*Any approved termination may be added to the minimum
equivalent length listed.
NOTE - It is acceptable to use any pipe size which fits
within the guidelines allowed in table 7.
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
fittings.
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.
Example
5 ft. plus 2 elbows of 2",
2-1/2" or 3" diameter pipe
Page 15
Piping Size Process
What is the
furnace capacity?
1
070, 090 or 110?
Which style termination
being used?
2
Standard or concentric?
See table 5.
Which needs
most elbows?
3
Intake or
exhaust?
How many elbows?
Count all elbows inside
4
and outside house.
Desired pipe size?
5
2", 2-1/2", 3"
What is the altitude of
6
the furnace installation?
Use table 7 to find max
intake or exhaust pipe
7
length. Includes all vent
pipe and elbows inside
and outside the house.
FIGURE 18