Page 22
Vent Piping Guidelines
NOTE - Lennox 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 re
quirements stated in the unit installation instruction – min
imum & maximum vent lengths, termination clearances,
etc. – apply and must be followed. Follow the instructions
provided with PoyPro by DuraVent and InnoFlue by Cen
trotherm venting system for assembly or if requirements
are more restrictive. The PolyPro by Duravent and In
noFlue by Centrotherm venting system must also follow
the uninsulated and unconditioned space criteria listed in
table 14.
The ML196DFE can be installed as either a Non-Direct
Vent or a Direct Vent gas central furnace.
NOTE - In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors. In
Non-Direct Vent installations, combustion air is taken from
indoors or ventilated attic or crawlspace and flue gases are
discharged outdoors.
Intake and exhaust pipe sizing -- Size pipe according to
tables 11 and 12. Count all elbows inside and outside the
home. Table 11 lists the minimum vent pipe lengths per
mitted. Table 12 lists the maximum pipe lengths permitted.
TABLE 11
MINIMUM VENT PIPE LENGTHS
ML196DFE
MODEL
MIN. VENT LENGTH*
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.
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 15.
In some applications which permit the use of several differ
ent sizes of vent pipe, a combination vent pipe may be
used. Contact Lennox' Application Department for assis
tance in sizing vent pipe in these applications.
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups
and may block the terminations.
Use the following steps to correctly size vent pipe diameter.
FIGURE 23
Piping Size Process
1
2
3
4
5
6
Which style termination
being used?
Standard or concentric?
Which needs
most elbows?
Intake or
exhaust?
How many elbows?
Count all elbows inside
and outside house.
Desired pipe size?
Use table 12 or 13 to find
max intake or exhaust pipe
length. Includes all vent
pipe and elbows inside
and outside the house.
What is the altitude of
the furnace installation?
7
What is the
furnace capacity?
NOTE - It is acceptable to use any pipe size which fits within
the guidelines allowed in table 12.
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.
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