Lennox SLP98UHV Installation Instructions Manual page 14

The SLP98UHV is installed only as a Direct Vent gas
central furnace.
NOTE - In Direct Vent installations, combustion air is tak-
en from outdoors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing -- Size pipe according to
tables 4 and 5. Count all elbows inside and outside the
home. Table 4 lists the minimum vent pipe lengths per-
mitted. Table 5 lists the maximum pipe lengths permitted.
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 7.
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.
Use the steps in figure 17 to correctly size vent pipe di-
ameter.
NOTE - It is acceptable to use any pipe size which fits
within the guidelines allowed in table 5.
Exhaust Pipe
Exhaust Pipe
Horizontal
Gas Furnace
12" ma x
of straight pip e
NOTE -
ward 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.
FIGURE 16
NOTE - The exhaust collar on all models is sized to ac-
commodate 2" Schedule 40 vent pipe. In horizontal ap-
plications, any transition to exhaust pipe larger than 2"
must be made in vertical runs of the pipe. Therefore a 2"
elbow must be added before the pipe is transitioned to
any size larger than 2". This elbow must be added to the
elbow count used to determine acceptable vent lengths.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations..
12" Min .
*Any approved termination may be added to the minimum equivalent length
listed.
Page 14
IMPORTANT
Piping Size Process
What is the
furnace capacity?
1
045, 070, 090,
110 or 135?
Which style termination
being used?
2
Standard or concentric?
See table 3.
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 5 or 6 to find
max intake or exhaust pipe
7
length. Includes all vent
pipe and elbows inside
and outside the house.
FIGURE 17
TABLE 4
MINIMUM VENT PIPE LENGTHS
SL998UHV MIN.EQUIV. VENT
MODEL LENGTH
070, 090, 110
15 ft*
135
EXAMPLE
5 ft. plus 2 elbows
of 2", 2-1/2" or 3"
diameter pipe
5 ft. plus 2 elbows of
3" diameter pipe