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.
Excessive exposure to contaminated combustion air will
result in safety and performance related problems.
Solvent cements are combustible. Keep away from heat,
sparks, and open flame. Use only in well ventilated areas.
Avoid breathing in vapor or allowing contact with skin or
eyes. Failure to follow this warning could result in fire,
property damage, personal injury, or death.
All combustion-air and vent pipes must be airtight and
watertight. Pipes must also terminate exactly as shown in Fig.
37, 38, 39, 40, or 41. Failure to follow this warning could
result in property damage, personal injury, or death.
NOTE: The minimum combustion-air and vent pipe length (each)
for these furnaces is 5 ft. Short pipe lengths (5-8 ft) may discharge
water droplets. These droplets may be undesirable, and a 12-in.
minimum offset pipe section is recommended, as shown in Fig. 35,
to reduce excessive droplets from exiting vent pipe outlet.
Combustion-Air and Vent Pipe Diameter
Determine combustion-air and vent pipe diameter.
1. Using Table 7, individually determine the smallest
combustion-air and vent pipe diameters. Pick the larger of
these 2 pipe 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 greater
than required or incomplete combustion, flame disturbance, or
flame sense lockout may occur.
NOTE: Do not count elbows or pipe sections in terminations or
within furnace. See shaded areas in Fig. 37, 38, 39, 40, and 41.
EXAMPLE:
An 080-14 size furnace located in Indianapolis, elevation
650 ft above sea level, could be installed in an application
requiring 3 elbows and 17 ft of vent pipe, along with 5
elbows and 16 ft of combustion-air pipe. Table 6 indicates
this application would allow a 1-1/2-in. diameter vent pipe,
but require a 2-in. diameter combustion air pipe (1-1/2-in.
pipe is good for 20 ft with 3 elbows, but only 10 ft with 5
elbows). Therefore, 2-in. 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
installation were in Albuquerque, elevation 5250 ft above
sea level, installation would require 2-in. vent pipe and
combustion-air pipe. At 5001- to 6000-ft elevation, 1-1/2-
in. pipe is not allowed with 5 elbows, but 2-in. pipe is good
for 68 ft with 5 elbows.
Combustion-Air and Vent Pipe Attachment
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.
1. Attach combustion-air pipe as follows:
a. Determine location of combustion-air intake pipe connec-
tion to combustion-air intake housing as shown in Fig. 34
for application.
b. Reposition combustion-air intake housing plug fitting in
appropriate unused intake housing connection.
c. Insert perforated disk assembly (factory supplied) in intake
housing where combustion-air intake pipe will be con-
nected.
d. Install pipe support (factory-supplied in loose parts bag)
into selected furnace casing combustion-air pipe hole. Pipe
support should be positioned to bottom of casing hole.
e. Insert 2-in. diameter pipe into intake housing.
TABLE 5—APPROVED COMBUSTION-AIR AND VENT PIPE, FITTING AND CEMENT MATERIALS
ASTM SPECIFICATION
(MARKED ON MATERIAL)
MATERIAL PIPE FITTINGS SOLVENT CEMENT AND PRIMERS DESCRIPTION
D1527 ABS Pipe — — Schedule-40
D1785 PVC Pipe — — Schedule-40
D2235 For ABS — —
Solvent
Cement
For ABS
D2241 PVC Pipe — — SDR-21 & SDR-26
D2466 PVC — Fittings — Schedule-40
D2468 ABS — Fittings — Schedule-40
D2564 For PVC — —
Solvent
Cement
For PVC
D2661 ABS Pipe Fittings — DWV at Schedule-40 IPS sizes
D2665 PVC Pipe Fittings — DWV
F438 CPVC — Fittings — Schedule-40
F441 CPVC Pipe — — Schedule-40
F442 CPVC Pipe — — SDR
F493 For CPVC — —
Solvent
Cement
For CPVC
F628 ABS Pipe — — Cellular Core DWV at Schedule-40 IPS sizes
F656 For PVC — — Primer For PVC
F891 PVC Pipe — — Cellular Core Schedule-40 & DWV
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