Lennox ML193DFE Series Unit Information page 24

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TABLE 12
MINIMUM VENT PIPE LENGTHS
ML193DFE MODEL
045, 070, 090
*Any approved termination may be added to the minimum length listed.
Two 45 degree elbows are equivalent to one 90 degree elbow.
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 16.
In some applications which permit the use of several dif-
ferent 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.
CAUTION
Do not use screens or perforated metal in exhaust
or intake terminations. Doing so will cause freeze-
ups and may block the terminations.
MIN. VENT LENGTH*
15 ft or 5ft plus 2 elbows or 10 ft
plus 1 elbow
Use the following steps to correctly size vent pipe diam-
eter.
1
2
3
4
5
6
7
NOTE - It is acceptable to use any pipe size which fits within the
guidelines allowed in table 13.
NOTE - All horizontal runs of exhaust pipe must slope back to-
ward 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.
Page 24
Piping Size Process
What is the
furnace capacity?
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?
What is the altitude of
the furnace installation?
Find max intake or
exhaust pipe length.
Includes all vent pipe and
elbows inside and outside
the house.
FIGURE 24