Vent Piping Guidelines - Lennox MERIT Series Installation Instructions Manual

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 Du-
raVent or InnoFlue® by Centrotherm venting system the
vent pipe requirements stated in the unit installation in-
struction – minimum & maximum vent lengths, termination
clearances, etc. – apply and must be followed. Follow the
instructions provided with PoyPro by DuraVent and Inno-
Flue by Centrotherm venting system for assembly or if re-
quirements are more restrictive. The PolyPro by Duravent
and InnoFlueby Centrotherm venting system must also
follow the uninsulated and unconditioned space criteria
listed in TABLE 8.
The ML296DFV 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 or ventilated attic or crawlspace and
flue gases are discharged outdoors. In Direct Vent instal-
lations, 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 7. Count all elbows inside and out-
side the home. Table 6 lists the minimum vent pipe lengths
permitted. Table 7 lists the maximum pipe lengths permit-
ted.
TABLE 6
MINIMUM VENT PIPE LENGTHS
ML296DFV 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 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 - 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 - Lennox offers a glueless vent adapter kit 17H92
as an option for exhaust exiting at the furnace top cap
coupling.
MIN. VENT LENGTH*
15 ft or 5ft plus 2 elbows or
10 ft plus 1 elbow
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.
NOTE - If right side venting option is used, you must in-
clude the elbow at the furnace in the elbow count. If tran-
sitioning to 3" dia pipe, this elbow equates to 20' of equiv-
alent vent length for all models.
Use the following steps to correctly size vent pipe diam-
eter.
1
2
3
How many elbows?
4
Count all elbows inside
and outside house.
5
What is the altitude of
6
the furnace installation?
7
Page 17
Piping Size Process
What is the
furnace capacity?
Which style termination
being used?
Standard or
concentric?.
Which needs
most elbows?
Intake or
exhaust?
Desired pipe size?
Find max intake or
exhaust pipe length.
Includes all vent pipe and
elbows inside and outside
the house.
FIGURE 21