507270-03 Page 17 of 60Issue 1917
Exhaust Piping
See Figure 25 and Figure 26
1.  In areas where piping penetrates joist or interior walls, 
hole must be large enough  to  allow  clearance  on all 
sides of pipe through center of hole using a hanger.
2.  When  furnace  is  installed  in  a  residence  where  unit 
is  shut  down  for  an  extended  period  of  time,  such 
as  a  vacation  home,  make  provisions  for  draining 
condensate collection from trap and lines.
3.  Route  piping  to  outside  of  structure.  Continue  with 
installation  following  instructions  given  in  piping 
termination section.
Do  not  discharge  exhaust  into  an  existing  stack  or 
stack that also serves another gas appliance. If vertical 
discharge through an existing unused stack is required, 
insert PVC pipe inside the stack  until  the  end  is  even 
with the top or outlet end of the metal stack.
 CAUTION
The exhaust vent pipe operates under positive pressure 
and  must  be  completely  sealed  to  prevent  leakage  of 
combustion products into the living space.
 CAUTION
Vent Piping Guidelines
This gas  furnace  can be  installed  as  either  a Non-Direct 
Vent or a Direct Vent gas central furnace.
NOTE: In non-Direct Vent installations, combustion air is 
taken from indoors and ue gases are discharged outdoors. 
In Direct Vent installations, combustion air is taken from 
outdoors and ue gases are discharged outdoors.
Intake  and  exhaust  pipe  sizing  -  Size  pipe  according  to 
Table  4 and Table 5A through Table 6C. Table 4  lists the 
minimum vent pipe lengths permitted. Table 5A and Table 
5B list the maximum pipe lengths permitted for A93UH1D 
and 92G1UH-P. Table 6A through Table 6C list the maximum 
pipe lengths permitted for A95UH1D and 95G1UH-P.
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 8.
In  some  applications  which  permit  the  use  of  several 
different sizes of vent pipe, a combination vent pipe may 
be used. Contact Allied Air Technical Service for assistance 
in sizing vent pipe in these applications.
Figure 23. 
NOTE: It  is  acceptable  to  use  any  pipe  size  which  ts 
within  the  guidelines  allowed  in  Table  5A  and  Table  5B, 
and Table 6A through Table 6C.
NOTE: The  exhaust  collar  on  all  models  is  sized  to 
accommodate  2”  Schedule  40  vent  pipe.  In  horizontal 
applications, transition to exhaust pipe larger than 2” must 
be made in vertical runs of the pipe. 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. 
Capacity Min. Vent Length*
045, 070, 090, 110
15 ft. or 
5 ft plus 2 elbows or 
10 ft plus 1 elbow
135**
* Any approved termination may be added to the minimum 
length listed.
** This gas furnace must have 3” to 2” reducing elbow 
(supplied or eld replacement Canadian kit) installed directly 
into unit ue collar.
Table 4. Minimum Vent Pipe Lengths
Do not  use  screens  or perforated  metal  in exhaust  or 
intake terminations. Doing so will cause freeze-ups and 
may block the terminations.
 IMPORTANT