NOTE:
Furnace combustion-air and vent pipe connections are
sized for 2-in. pipe. Any pipe size change should be made outside
furnace casing in vertical pipe. (See Fig. 18.) This allows proper
drainage of vent condensate.
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
6 for required clearances.
Furnace combustion-air and vent pipe connections must be at-
tached as shown in Fig. 19. Combustion-air intake plug fitting and
inducer housing alternate vent cap may need to be relocated in
some applications.
NOTE:
Slope combustion-air and vent pipes a minimum of 1/4
in. per linear ft with no sags between hangers.
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 8 with
Armaflex-type insulation.
CAUTION:
Combustion air must not be taken from
inside structure because inside 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 allow-
ing contact with skin or eyes. Failure to follow this
warning could result in fire, property damage, personal
injury, or death.
WARNING:
All combustion-air and vent pipes must be
airtight and watertight. Pipes must also terminate exactly
as shown in Fig. 22, 23, 24, 25, or 26. 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. 20,
to reduce excessive droplets from exiting vent pipe outlet.
B.
Combustion-Air and Vent Pipe Diameter
Determine combustion-air and vent pipe diameter.
1. Using Table 7, individually determine the 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.
Fig. 18—Combustion-Air and Vent Pipe Diameter
Transition Location and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
TABLE 6—COMBUSTION-AIR AND VENT PIPE
TERMINATION CLEARANCES
LOCATION
CLEARANCE (FT)
U.S.A.
Canada
Above grade level or above antici-
pated 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 (windows or
doors which can be opened) or
combustion-air opening
1
1
From service regulator vent, electric
and gas meters, and relief equipment
4*
6‡
Above grade when adjacent to public
walkway
Note 1
Note 2
* Horizontal distance.
† 18 in. above roof surface in Canada.
‡ 36 in. to electric meter in Canada only.
NOTES:
1. 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.
2. Vent termination can not terminate less than 2 ft horizontal and 7 ft above
public walkway or where condensate vapor or droplets may be a hazard.
Fig. 19—Combustion-Air and Vent Pipe Connections
A99024
AIR
FLOW
DOWNFLOW
COMBUSTION-
AIR
COMBUSTION-
AIR
VENT
VENT
Select 1 vent pipe connection and
1 combustion-air pipe connection.
NOTE:
—16—
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