42
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
A93034
Fig. 41 -- Combustion--Air and Vent Pipe Diameter
Transition Location and Elbow Configuration
COMBUSTION-AIR
PIPE (DIRECT
VENT/2 PIPE)
BURNER
BOX
COMBUSTION – AIR
INTAKE HOUSING
3/8 ID TUBE
TRAP
TO OPEN
DRAIN
3/16
DRILL
4″MIN
(102 mm)
COMBUSTION-AIR
PIPE (NON-DIRECT
VENT/1-PIPE)
A05093
Fig. 42 -- Air Intake Housing Plug Fitting Drain
EXAMPLE:
An 080--12 size furnace located in Indianapolis, elevation
650 ft (198 M) above sea level, could be installed as either a
direct vent/2-pipe system that requires 3 elbows and 32 ft (10
M) of vent pipe, along with 5 elbows and 34 ft (10 M) of
combustion-air pipe OR a non-direct vent/1-pipe system that
requires 3 elbows and 32 ft (10 M) vent pipe.
For a direct vent/2-pipe system, Table 13 indicates this
application would allow a 2--in. (51 mm) diameter vent pipe,
but require a 2-1/2 in. (64 mm) diameter combustion air pipe.
According to Table 13, 2-in. (51 mm) diameter pipe is good
for35ft(11M)with3elbows,butonly30ft(9M)with5
elbows. Therefore, 2-1/2 in. (64 mm) diameter pipe must be
used for both vent and combustion-air pipes since larger
required diameter must always be used for both pipes.
For a non-direct vent/1-pipe system, Table 13 indicates that
this application would allow a 2-in. (51 mm) diameter vent
pipe.
If same installations were in Albuquerque, elevation 5250 ft
(1600 M) above sea level:
For a direct vent/2-pipe system, Table 13 indicates that 2-1/2
in. (64 mm) diameter vent pipe and combustion-air pipe are
required.
For a non-direct vent/1-pipe system, Table 13 indicates that
2-1/2-in. (64 mm) diameter vent pipe is required.
If same applications are to be installed at 5001 to 6000 ft
(1524 to 1829 M)elevation:
For a direct vent/2-pipe system, 2-in. (51 mm) pipe is only
good for 23 ft (7 M) (with 3 elbows) and 17 ft (5 M)(with 5
elbows). Therefore, 2-1/2 in. (64 mm) diameter combustion air
and vent pipe must be used.
For a non-direct vent/1-pipe system, a 2-in. (51 mm)
diameter pipe is only good for 23 ft (7 M) with 3 elbows. A
2-1/2-in. (64 mm) diameter vent pipe must be used.
352AAV
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