Page 23
Exhaust and Intake Piping (FIGURE 24 and FIGURE
Route piping to outside of structure. Continue with instal
-
lation following instructions given in piping termination
section.
WARNING
Carbon Monoxide Poisoning Hazard
Cutting or altering exhaust or air intake pipes, which
are located in the blower compartment, could result
in Carbon Monoxide Poisoning or Death.
CAUTION
Do not discharge exhaust into an existing stack
or stack that also serves another gas appliance. If
vertical discharge through an existing unused stack
is required, insert PVC pipe inside the stack until the
end is even with the top or outlet end of the metal
stack.
CAUTION
The exhaust vent pipe operates under positive
pressure and must be completely sealed to prevent
leakage of combustion products into the living
space.
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 InnoFlue by Centrotherm venting system must also
follow the uninsulated and unconditioned space criteria
listed in table15.
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 tak
-
en 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
-
TABLE 12 (minimum) and TABLE 13 (maximum). Count
all elbows inside and outside the home.
NOTE -
Lennox offers a glueless vent adapter kit 17H92 as an
option for exhaust exiting at the furnace top cap coupling.
TABLE 12
MINIMUM VENT PIPE LENGTHS
ML196DFE MODEL
MIN. VENT LENGTH*
045, 070, 090, 110
15 ft or 5ft plus 2 elbows or 10 ft
plus 1 elbow
*Any approved termination may be added to the minimum length listed.
Two 45 degree elbows are equivalent to one 90 degree elbow.
*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.
Use the following steps to correctly size vent pipe diam
-
eter.
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?
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?
FIGURE 23
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.
CAUTION
Do not use screens or perforated metal in exhaust
or intake terminations. Doing so will cause freeze-
ups and may block the terminations.
