Lennox MERIT Series Installation Instructions Manual page 16

TABLE 6
MINIMUM VENT PIPE LENGTHS*
MODEL
045,070, 090, 110
*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 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.
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze-ups and
may block the terminations.
NOTE - Lennox offers a glueless vent adapter kit 17H92
as an option for exhaust exiting at the furnace top cap
coupling.
Use the following steps to correctly size vent pipe diam-
eter.
MIN. VENT LENGTH
15 ft. or
5 ft plus 2 elbows or
10 ft plus 1 elbow
Page 16
Piping Size Process
What is the
furnace capacity?
1
045, 070, 090 or
Which style termination
being used?
2
Standard or concentric?
See table 5.
Which needs
most elbows?
3
exhaust?
How many elbows?
Count all elbows inside
4
and outside house.
Desired pipe size?
5
2", 2-1/2", 3"
What is the altitude of
6
the furnace installation?
Use table 7 or 8 to find
max intake or exhaust pipe
7
length. Includes all vent
pipe and elbows inside
and outside the house.
FIGURE 22
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.
110?
Intake or