Combustion-air and vent pipes must terminate together in same
atmosphere pressure zone, either through roof or sidewall (roof
termination preferred), using accessory termination kit. See Table
4 for required clearances.
Furnace combustion-air and vent pipe connections must be at-
tached as shown in Fig. 28. Combustion-air intake plug fitting and
inducer housing alternate vent cap may need to be relocated in
some applications.
CAUTION:
When combustion-air pipe is installed
above a suspended ceiling, pipe must be insulated with
3/8-in. thick Armaflex-type insulation. Combustion-air
pipe should also be insulated when it passes through
warm, humid space.
CAUTION:
When vent pipe is exposed to temperatures
below freezing, such as when it passes through an
unheated space or when a chimney is used as a raceway,
pipe must be insulated as shown in Table 6 with
Armaflex-type insulation.
CAUTION:
Combustion air must not be taken from
inside structure because that air is frequently contami-
nated 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 prod-
ucts. 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.
WARNING:
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.
TABLE 4—COMBUSTION-AIR AND VENT PIPE
TERMINATION CLEARANCES
LOCATION
CLEARANCE (FT)
U.S.A.
Canada
Above grade level or above
anticipated snow depth
1
1†
Dryer vent
3
3
From plumbing vent stack
3
3
From any mechanical fresh
air intake
1
6
For furnaces with an input
capacity less than 100,000
Btuh–from any non-
mechanical air supply (win-
dows or doors which can
be opened) or combustion-
air opening
1
1
For furnaces with an input
capacity greater than
100,000 Btuh–from any
non-mechanical air supply
(windows or doors which
can be opened) or
combustion-air opening
1
3
From service regulator
vent, electric and gas
meters, and relief equip-
ment
4*
6‡
Above grade when adjacent
to public walkway
7
7
* Horizontal distance.
† 18 in. above roof surface in Canada.
‡ 36 in. to electric meter in Canada only.
NOTES:
1. If installing 2 adjacent 355MAV Furnaces, refer to Multiventing and Vent
Terminations section for proper vent configurations.
2. When locating combustion-air and vent terminations, consideration must be
given to prevailing winds, location, and other conditions which may cause
recirculation of the appliance’s own flue products or the flue products of
adjacent vents. Recirculation can cause poor combustion, inlet condensate
problems, and accelerated corrosion of heat exchangers.
Fig. 27—Combustion-Air and Vent Pipe Diameter
Transition Location and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
Fig. 28—Combustion-Air and Vent Pipe Connections
A93083
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