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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
Table 6 and Table 7A through Table 7B. Table 6 lists the
minimum vent pipe lengths permitted. Table 7A and Table
7B 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.
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.
Capacity
045, 070, 090, 110
Table 6. Minimum Vent Pipe Lengths
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
507271-02
Min. Vent Length*
15 ft. or
5 ft plus 2 elbows or
10 ft plus 1 elbow
Issue 1917
Use the following steps to correctly size vent pipe diameter.
Furnace capacity?
1
Which termination?
2
Which needs most
3
elbows?
How many?
4
Desired pipe size?
5
What is the altitude?
6
Use Table 7 to find
7
max pipe length.
Figure 22.
045, 070,
090, 110
Standard or
Concentric?
See Table 3
Intake or
Exhaust?
2", 2-1/2"
or 3"
Page 17 of 51
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