507581-04
Page 18 of 59
Issue 1933
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
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.
NOTE
:
The exhaust collar on all models is sized to
accommodate 2” Schedule 40 vent pipe. When vent
pipe which is larger than 2” must be used in an upflow
application, a transition must be applied at the exhaust
collar in order to properly step to the larger diameter
vent pipe. Contact Allied Air Technical Service for more
information concerning sizing of vent systems which
include multiple pipe sizes.
NOTE:
All horizontal runs of exhaust pipe must slope back toward
unit. A minimum of 1/4” (6 mm) drop for each 12” (305 mm) 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 sages or low spots.
Figure 23. Exhaust Pipe
Horizontal Application
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
IMPORTANT
Table 4. Minimum Vent Pipe Lengths
Model
Min. Vent Length*
030,045,070,090,110
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.
Use the following steps to correctly size vent pipe diameter.
030, 045,
070, 090,
110
Standard or
Concentric?
See Table 3
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 5 to find
max pipe length.
7
Figure 24. Minimum Vent Pipe Lengths
