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In some applications which permit the use of several differ
ent sizes of vent pipe, a combination vent pipe may be used.
Contact Lennox' Application Department for assistance in
sizing vent pipe in these applications.
Use the steps in figure 25 to correctly size vent pipe diame
ter.
NOTE - It is acceptable to use any pipe size which fits within
the guidelines allowed in table 24.
FIGURE 24
NOTE - Exhaust pipe MUST be glued to furnace exhaust fittings.
NOTE - All horizontal runs of exhaust pipe must slope back to
ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm)
of horizontal run is mandatory for drainage.
NOTE - Exhaust piping should be checked carefully to make
sure there are no sags or low spots.
12” ma x
of straight pip
e
Exhaust Pipe
12” Min.
Horizontal
Gas Furnace
NOTE - The exhaust collar on all models is sized to accommo
date 2” Schedule 40 vent pipe. In horizontal applications, 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 informa
tion concerning sizing of vent systems which include multiple
pipe sizes.
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups
and may block the terminations.
TABLE 23
MINIMUM VENT PIPE LENGTHS
SLP99UHV
MODEL
MIN. EQUIV.
VENT
LENGTH
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
135
5 ft. plus 2 elbows of 3”
diameter pipe
*Any approved termination may be added to the minimum equivalent length
listed. Two 45 degree elbows are equivalent to one 90 degree elbow.
Flue Coupling
The provided flue coupling must be attached (do not use
glue) to the exhaust coupling on the furnace top panel. Use
provided bands. See steps below and FIGURE 26.
1 - Remove the caution sticker from flue coupling .
2 - Fully insert flue coupling with both bands loosely at
tached on the furnace exhaust coupling.
3 - Insert PVC exhaust pipe through flue coupling. Ensure
vent pipe is fully seated into exhaust coupling. Tighten
both top and bottom bands to 40 in lbs. See figure 26.
FIGURE 25
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 ex
haust 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 26
Furnace
Top Band
(torque to 40in−lbs)
PVC
Exhaust Pipe
Flue Coupling To Exhaust Coupling
Top Panel
Bottom Band
(torque to 40in−lbs)
Furnace
Exhaust Coupling
Flue Coupling
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