Page 24
The ML193UHE 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 and flue gases are discharged out
-
doors. In Direct Vent installations, combustion air is taken
from outdoors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing -- Size pipe according to
TABLE 12 (minimum pipe lengths) and TABLE 13 (maxi
-
mum pipe lengths. Count all elbows inside and outside the
home. TABLE 14 lists maximum pipe lengths for furnaces
installed in a closet or basement using ventilated attic or
crawl space for intake air.
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.
NOTE -
The exhaust collar on all models is sized to ac
-
commodate 2” Schedule 40 vent pipe. In horizontal ap
-
plications, any transition to exhaust pipe larger than 2”
must be made in vertical runs of the pipe. Therefore a 2”
elbow must be added before the pipe is transitioned to
any size larger than 2”. This elbow must be added to the
elbow count used to determine acceptable vent lengths.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
Horizontal Installation Offset Requirements
NOTE
- Exhaust pipe MUST be glued to furnace exhaust fitting,
unless the optional glueless vent adapter kit 17H92 is used..
NOTE -
ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm)
of horizontal run is mandatory for drainage.
NOTE
- Exhaust piping should be checked carefully to make
sure there are no sags or low spots.
Exhaust Pipe
Horizontal
Gas Furnace
12” Min.
12” Max.
FIGURE 23
TABLE 12
MINIMUM VENT PIPE LENGTHS
ML193UHE Model
MIN. VENT LENGTH*
030, 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. Two 45 degree elbows are the equivalent of one
90 degree elbow.
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 24
IMPORTANT
Do not use screens or perforated metal in exhaust
or intake terminations. Doing so will cause freeze-
ups and may block the terminations.
