508151-01
Issue 2104
Page 33 of 72
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 21.
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 Services department
for assistance in sizing vent pipe in these applications.
NOTE:
It is acceptable to use any pipe size which fits within
the guidelines allowed in Table 19A through Table 19C.
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.
NOTE:
If right side venting option is used, you must include
the elbow at the furnace in the elbow count. If transitioning
to 3” dia pipe, this elbow equates to 20’ of equivalent vent
length for all models.
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
IMPORTANT
Model
Min. Vent Length
All
15 ft. or
5 ft. plus 2 elbows or
10 ft. plus 1 elbow
*Any approved termination may be added to the minimum
length listed.
Table 18.
Minimum Vent Pipe Lengths
Use the following steps to correctly size vent pipe diameter.
045, 070,
090, 110
Standard or
Concentric?
See Table 17
Intake or
Exhaust?
1-1/2”, 2”,
2-1/2”,
or 3”
Furnace capacity?
1
Which termination?
2
Which needs most
elbows?
3
How many?
4
Desired pipe size?
5
What is the altitude?
6
Use Table 19A
through 19C to find
max pipe length.
7
Figure 24.