Lennox G61MPV Service Manual page 51

A−Vent Piping Guidelines
The G61MPV 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 in Direct Vent applications
and exhaust pipe sizing in Non-Direct Vent applications −−
Size pipe according to tables 36 and 37. Table 36 lists the
minimum equivalent vent pipe lengths permitted. Table 37
lists the maximum equivalent pipe lengths permitted.
Maximum vent length is defined as:
Total length (linear feet) of pipe,
Plus Equivalent length (feet) of fittings,
Plus Equivalent length (feet) of termination.
NOTE − Include ALL pipe and ALL fittings, both in
doors and outdoors.
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 38.
Upflow and Downflow Application
Rooftop Termination
*12" Min.
Exhaust Pipe Offset
*12" Min.
Horizontal Application
Rooftop Termination
*A minimum of 1/4" (6mm) drop for each 12" (305mm) of horizontal run is mandatory for drainage
NOTE − The exhaust pipe should be offset a minimum of 12
inches to avoid the possibility of water droplets being re-
leased from the exhaust termination. The minimum ex-
haust vent length is 15 ft. Shorter exhaust vent lengths may
result in the discharge of water droplets from the exhaust
termination, in spite of the 12−inch vertical offset.
Each 90° elbow (including those provided with the furnace)
of any diameter is equivalent to 5 feet (1.52m) of vent pipe
of the same diameter. Two 45° elbows are equivalent to
one 90° elbow of the same diameter. One 45° elbow is
equal to 2.5 feet (.76m) of vent pipe of the same diameter.
In some applications which permit the use of several differ-
ent sizes of vent pipe, a combination vent pipe may be
used. Contact the Application Department for assistance in
sizing vent pipe in these applications.
NOTE − On G61MPV−071, −091 and −111 units, sweep el-
bows must be used for all 90° elbows in the venting
system when 2", 2−1/2" or 3" vent pipe is used. On
G61MPV−135, sweep elbows must be used for all 90° el-
bows in the venting system when 3" vent pipe is used.
Sweep elbows are recommended for use in vent sys-
tems of other G61MPV units.
Upflow and Downflow Application
FIGURE 22
Page 51
*12" Min.
Side Wall Termination
*12" Min.
Horizontal Application
Side Wall Termination