Page 21
Flue Coupling 
The  provided  ue  coupling  must  be  attached  to  the  ex-
haust coupling on the furnace top panel. Use provided 
bands. See steps below. and FIGURE 26.
1 -   Remove the caution tag from the ue coupling.
2 -   Fully  insert  ue  coupling  with  both  bands  loosely 
attached on the furnace exhaust coupling.
3 -   Insert  PVC  exhaust  pipe  through  ue  coupling 
Ensure vent pipe is fully seated into exhaust 
coupling.
4 -  Tighten both top and bottom bands to 40in-lbs.
NOTE - Do  not  use  any  type  of  glue  or  silicone 
to  attach  the  ue  coupling  to  the  furnace  exhaust 
coupling.
Furnace
Top Band
(torque to 40in-lbs)
PVC
Exhaust Pipe
Top Panel
Flue Coupling To Exhaust Coupling
Bottom Band
(torque to 40in-lbs)
Flue Couplig
Furnace
Exhaust Coupling
FIGURE 26 
Crawl Space and Extended Horizontal Venting
Lennox provides kit 51W18(USA) and kit 15Z70 (Canada) 
to  install  2”  or  3”  PVC  exhaust  piping  through  the  oor 
joists and into the the crawl space. This kit can also be 
used as a supplemental drain for installations with con-
densate run back in the vent pipe (ie. long horizontal runs, 
unconditioned spaces, etc.). See FIGURE 27 and FIG-
URE 28
Venting In A Crawl Space
Basement Floor
KIT 51W18
(USA)
KIT 15Z70
(CANADA)
FIGURE 27 
 
Long Horizontal Runs
KIT 51W18
(USA)
KIT 51Z70
(CANADA)
FIGURE 28 
Guidelines for Vent Terminations
In Direct Vent applications, combustion air is taken from 
outdoors  and  the  ue  gases  are  discharged  to  the  out-
doors. The SLP99UHV is classied as a direct vent, Cate-
gory IV gas furnace.
In Direct Vent applications, the vent termination is limited 
by local building codes. In the absence of local codes, re-
fer to the current National Fuel Gas Code ANSI Z223-1/
NFPA 54 in U.S.A., and current CSA-B149 Natural Gas 
and Propane Installation Codes in Canada for details.
Position termination according to location given in  gure 
20. In addition, position termination so it is free from any 
obstructions and 12” above the average snow accumula-
tion.
At vent termination, care must be taken to maintain protec-
tive coatings over building materials (prolonged exposure 
to exhaust condensate can destroy protective coatings). 
It is recommended that the exhaust outlet not be located 
within 6 feet (1.8m) of an outdoor AC unit because the 
condensate can damage the painted coating.
NOTE - See TABLE 9 for maximum allowed exhaust pipe 
length  without  insulation  in  unconditioned  space  during-
winter design temperatures below 32°F (0°C). If required 
exhaust  pipe  should  be  insulated  with  1/2”  (13mm)  Ar-
maex or equivalent. In extreme cold climate areas, 3/4” 
(19mm) Armaex or equivalent  may be necessary. Insu-
lation must be protected from deterioration. Armaex with 
UV  protection  is  permissable.  Basements  or  other  en-
closed areas that are not exposed to the outdoor ambient  
temperature and are above 32 degrees F (0°C) are to be 
considered conditioned spaces.
 IMPORTANT
Do not use screens or perforated metal in exhaust or 
intake terminations. Doing so will cause freeze-ups and 
may block the terminations.
 IMPORTANT
For Canadian Installations Only:
In accordance to CSA International B149 installation 
codes, the minimum allowed distance between the 
combustion air intake inlet and the exhaust outlet of other 
appliances shall not be less than 12 inches (305mm).