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TABLE 6
MINIMUM VENT PIPE LENGTHS
ML193DF
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 10.
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 21
Piping Size Process
1
2
3
4
5
6
Which style termination
being used?
Standard or concentric?
See table 5.
Which needs
most elbows?
Intake or
exhaust?
How many elbows?
Count all elbows inside
and outside house.
Desired pipe size?
2”, 2-1/2”, 3”
Use table 7 or 8 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?
045, 070, 090 or
110?
NOTE
- It is acceptable to use any pipe size which fits within
the guidelines allowed in table 7.
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.
