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506501-01 Page 17 of 48Issue 1031
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 flue gases are discharged outdoors.
In Direct Vent installations, combustion air is taken from
outdoors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing - Size pipe according to Tables
4 and 5. Table 4 lists the minimum vent pipe lengths
permitted. Table 5 lists the maximum pipe lengths permitted.
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 6.
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.
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
IMPORTANT
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.
EXHAUST PIPE
Horizontal Application
Figure 20
Use the following steps to correctly size vent pipe diameter.
*Any approved termination may be added to the minimum length
listed.
**This gas furnace must have 3" to 2" reducing ell (supplied or field
replacement Canadian kit) installed directly into unit flue collar.
MINIMUM VENT PIPE LENGTHS
Table 4