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 allowed for each pipe.
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 080-12 size furnace located in Indianapo-
lis, elevation 650 ft above sea level, could be installed in an
application requiring 3 elbows and 32 ft of vent pipe, along
with 5 elbows and 34 ft of combustion-air pipe. Table 7
indicates this application would allow a 2-in. diameter vent
pipe, but require a 2-1/2 in. diameter combustion air pipe
(2-in. pipe is good for 35 ft with 3 elbows, but only 30 ft
with 5 elbows). Therefore, 2-1/2 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 2-1/2 in. vent
pipe and combustion-air pipe. At 5001- to 6000-ft eleva-
tion, 2-in. pipe is only good for 17 ft with 5 elbows, and
2-1/2 in. pipe is good for 70 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 to furnace as follows:
Fig. 32—Control Center
A02017
LHT
OFF
DLY
ON
OFF
W2
BLW
24-V-THERMOSTAT
TERMINALS
SETUP SWITCHES
LOW-HEAT ONLY AND
BLOWER OFF-DELAY
TWINNING AND/OR
COMPONENT TEST
TERMINAL
ACRDJ - AIR CONDITIONING
RELAY DISABLE JUMPER
TRANSFORMER 24-VAC
CONNECTIONS
PL1 - LOW VOLTAGE MAIN
HARNESS CONNECTOR
PL3
HUMIDIFIER TERMINAL
(24-VAC 0.5 AMP MAX.)
3-AMP FUSE
LED OPERATION &
DIAGNOSTIC LIGHT
115-VAC (L2) NEUTRAL
CONNECTIONS
PL2 - HOT SURFACE
IGNITER & INDUCER
MOTOR CONNECTOR
115-VAC (L1) LINE
VOLTAGE CONNECTION
EAC-1 TERMINAL
(115-VAC 1.0 AMP MAX.)
BLOWER SPEED
SELECTION TERMINALS
HI HEAT
LO HEAT
SPARE-1
SPARE-2
COOL
Y1
DHUM
G
COM
24V
WW1
Y/Y2
R
TEST/TWIN
HUM
1 2 3
PL
T
A
CRDJ
0.5-AMP024 VAC
FUSE 3-AMP
SEC-1
SEC-2
PL1
NEUTRAL-L2
1
EAC-2
BHT/CLR
BHI/LOR
PL3 1
BLWR
COOL
SPARE-1
SPARE-2
1-AMP@115 VAC
EAC-1
PR-1
IDR
HSIR
IDM
IHI/LOR
PL2
1
HSI HI LO
STATU
S
C
OD
EL
E
D
HI HEA
T
LO HEA
T
L1
Fig. 33—Combustion-Air and Vent Pipe Diameter
Transition Location and Elbow Configuration
A93034
FURNACE
PIPE DIAMETER
TRANSITION IN
VERTICAL SECTION
NOT IN
HORIZONTAL
SECTION
27