508146-01
Issue 2051
Page 3
5
of 7
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Vent Piping Guidelines
NOTE:
Comfort-Aire/Century has approved the use of
DuraVent® and Centrotherm manufactured vent pipe and
terminations as an option to PVC. When using the
PolyPro® by DuraVent or InnoFlue® by Centrotherm
venting system the vent pipe requirements stated in the
unit installation instruction – minimum & maximum vent
lengths, termination clearances, etc. – apply and must be
followed. Follow the instructions provided with PoyPro by
DuraVent and InnoFlue by Centrotherm venting system for
assembly or if requirements are more restrictive. The
PolyPro by Duravent and InnoFlue by Centrotherm venting
system must also follow the uninsulated and unconditioned
space criteria listed in Table 23.
The GUH97M is installed as a Direct Vent gas central
furnace only.
NOTE:
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
Table 21 through Table 22B. Count all elbows inside and
outside the home. Table 21 lists the minimum vent pipe
lengths permitted. Table 22A through Table 22B list 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 24.
In some applications which permit the use of several
different sizes of vent pipe, a combination vent pipe may be
used. Contact Comfort-Aire/Century
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. In horizontal
applications, any transition to exhaust pipe larger than 2”
must be made in vertical runs of the pipe. Therefore 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. See Figure 24.
NOTE:
It is acceptable to use any pipe size which fits
within the guidelines allowed in Table 22A and Table 22B.
NOTE
- Exhaust pipe MUST be glued to furnace exhaust fittings.
NOTE -
ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm)
of horizontal run is mandatory for drainage.
NOTE
- Exhaust piping should be checked carefully to make
sure there are no sags or low spots.
Exhaust Pipe
Horizontal
Gas Furnace
12” Min.
12” Max.
Figure 24.
Horizontal Installation Offset Requirements
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. Equiv.
Vent Length
Example
70
15 ft.*
5 ft. plus 2 elbows of 1-1/2", 2”, 2-1/2”
or 3” diameter pipe
90
5 ft. plus 2 elbows of 2”, 2-1/2”
or 3” diameter pipe
110
5 ft. plus 2 elbows of 2-1/2”
or 3” diameter pipe
135
5 ft. plus 2 elbows of 3”
diameter pipe
Table 21.
