22
9. Wipe excess cement from joint. A continuous bead of ce-
ment will be visible around perimeter of a properly made
joint.
10. Handle pipe joints carefully until cement sets.
11. Horizontal portions of the venting system shall be suppor-
ted to prevent sagging. Support combustion air piping (if
applicable) and vent piping a minimum of every 5 ft. (1.5
M) (3 ft. (0.9 M) for SDR--21 or --26 PVC) using perforated
metal hanging strap.
12. Slope combustion air piping (if applicable) and vent piping
downward towards furnace a minimum of 1/4--in. (6 mm).
per linear ft with no sags between hangers.
13. Horizontal portions of the venting system shall be installed
so as to prevent the accumulation of condensate.
14. Use appropriate methods to seal openings where combus-
tion air pipe (if applicable) and vent pipe pass through roof
or sidewall.
Combustion--Air and Vent Pipe Diameter
Determine combustion--air and vent pipe diameter.
1. Using Table 8, individually determine the diameter of the
combustion--air and vent pipe allowed. If different, pick the
larger of these two diameters and use this diameter for both
combustion--air and vent pipes.
2. When installing vent systems of short pipe length, use the
smallest allowable pipe diameter. Do not use pipe size great-
er than required or incomplete combustion, flame disturb-
ance, or flame sense lockout may occur.
NOTE
: Do not count elbows or pipe sections in terminations or
within furnace.
NOTE
: A 2--in. (51 mm) diameter pipe must be used within
furnace casing. Make all pipe diameter transitions outside furnace
casing. (See Fig. 24).
UNIT MAY NOT OPERATE
Failure to follow this caution may result in incomplete
combustion, flame disturbance, or flame sense lockout.
When installing combustion air and vent system of short
pipe length, the smallest allowable pipe diameter must be
used.
CAUTION
!
UNIT CORROSION HAZARD
Excessive exposure to contaminated combustion air may
result in safety and performance related problems.
Combustion air must not be taken from inside structure
because that air is frequently contaminated by halogens,
which include fluorides, chlorides, bromides, and iodides.
These elements are found in aerosols, detergents, bleaches,
cleaning solvents, salts, air fresheners, adhesives, paint, and
other household products. Locate combustion--air inlet as
far as possible from swimming pool and swimming pool
pump house.
CAUTION
!
EXAMPLE:
A 100,000 BTUH furnace located in Indianapolis, elevation
650 ft. (198.1 M) above sea level, could be installed as
either a direct vent/2--pipe system that requires 3 elbows and
28 ft. (8.5 M) of vent pipe, along with 5 elbows and 34 ft.
(10.3 M) of combustion--air pipe. Table 8 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 8, 2--in. (51 mm) diameter pipe
is good for 35 ft. (10.6 M) with 3 elbows, but only 25 ft.
(7.6 M) with 5 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.
If same installations were in Albuquerque, elevation 5250 ft.
(1600 M) above sea level:
Table 8 indicates that 2--1/2 in. (64 mm) diameter vent pipe
and combustion--air pipe are required.
If same applications are to be installed at 5001 to 6000 ft.
(1524 to 1829 M) elevation:
2--in. (51 mm) pipe is only good for 23 ft. (7.0 M) (with 3
elbows) and 13 ft. (3.9 M) (with 5 elbows). Therefore,
2--1/2 in. (64 mm) diameter combustion air and vent pipe
must be used.
Combustion Air Pipe
General
Furnace combustion--air connection must be attached as shown in
Fig. 25. Combustion--air intake housing plug may need to be
relocated in some applications.
NOTE
: All pipe joints must be cemented except attachment of
combustion--air pipe to inlet housing connection, since it may be
necessary to remove pipe for servicing.
NOTE
: A 2--in. (51 mm) diameter pipe must be used within the
furnace casing. Make all pipe diameter transitions outside furnace
casing. (See Fig. 24).
COMBUSTION-
AIR
COMBUSTION-
AIR
AIR
FLOW
VENT
VENT
UPFLOW
Select 1 vent pipe connection and
1 combustion-air pipe connection.
NOTE:
A06500
Fig. 25 -- Combustion Air and Vent Pipe Connections
Attachment of Combustion Air Pipe
NOTE
: Combustion air pipe system has the same diameter and
same length as the vent pipe as mentioned in section
“Combustion--Air and Vent Pipe Diameter.”
1. Determine location of combustion--air intake pipe connec-
tion to combustion--air intake housing as shown in Fig. 25.
2. Verify combustion--air intake housing plug fitting is in-
stalled in appropriate unused intake housing connection.
3. Install combustion--air pipe grommet (factory--supplied in
loose parts bag) into selected furnace casing combustion--air
pipe hole.
355B
A
V
