Vent Piping Guidelines - Lennox ML195UH Installation Instructions Manual

Vent Piping Guidelines

The ML195UH 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 outdoors.
In Direct Vent installations, combustion air is taken from out-
doors and flue gases are discharged outdoors.
Intake and exhaust pipe sizing −− Size pipe according to
tables 4 and . Table 4 lists the minimum vent pipe lengths
5
permitted. Table lists the maximum pipe lengths per-
5
mitted.
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 6.
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.
NOTE − The exhaust collar on all models is sized to ac-
commodate 2" Schedule 40 vent pipe. When vent pipe
which is larger than 2" must be used in an upflow applica-
tion, a transition must be applied at the exhaust collar in
order to properly step to the larger diameter vent pipe.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
Exhaust Pipe
Exhaust Pipe
Horizontal
Gas Furnace
12" ma x
of straight pip e
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.
FIGURE 20
TABLE 4
MINIMUM VENT PIPE LENGTHS
ML195UH
MODEL
045, 070, 090, 110, 135
*Any approved termination may be added to the minimum length listed.
12" Min .
MIN. VENT LENGTH*
15 ft. or
5 ft. plus 2 elbows or
10 ft. plus 1 elbow
Page 17
Use the following steps to correctly size vent pipe diameter.
1
Furnace capacity?
Which termination?
2
Which needs
3
most elbows?
How many?
4
Desired pipe size?
5
6
What is the altitude?
Use table 5 to find
7
max. intake or
exhaust pipe length.
FIGURE 21
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze−ups
and may block the terminations.
045, 070,
090, 110
or 135 btuh
Standard or
Concentric?
See table 3
Intake or
exhaust
2", 2 1/2"
or 3"