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31-5000724 Rev. 0
Vent Piping Guidelines
NOTE:
GE Appliances 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 21.
The NF97DM 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 20 through Table 23B. Count all elbows inside and
outside the home. Table 20 lists the minimum vent pipe
lengths permitted. Table 23A through Table 23B 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 22.
In some applications which permit the use of several
different sizes of vent pipe, a combination vent pipe may
be used. Contact GE Appliances Application 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 24.
NOTE:
The exhaust collar on all models is sized to
accommodate 2” Schedule 40 vent pipe. Contact the
Application Department 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” (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.
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
Table 20. Minimum Vent Pipe Lengths
Use the following steps to correctly size vent pipe diameter.
Figure 25.
070, 090,
110 or 135
btuh
Standard or
Concentric?
See Table 20
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 22 to find
max pipe length.
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