66832-UIM-D-1205
12
Unitary Products Group
GAS PIPING INSTALLATION
Properly sized wrought iron, approved flexible or steel pipe must be
used when making gas connections to the unit. If local codes allow the
use of a flexible gas appliance connection, always use a new listed con-
nector. Do not use a connector that has previously serviced another gas
appliance.
Some utility companies or local codes require pipe sizes larger than the
minimum sizes listed in these instructions and in the codes. The furnace
rating plate and the instructions in this section specify the type of gas
approved for this furnace - only use those approved gases. The instal-
lation of a drip leg and ground union is required. Refer to Figure 17.
IMPORTANT: An accessible manual shutoff valve must be installed
upstream of the furnace gas controls and within 6 feet (1.8 m) of the fur-
nace. Refer to Figures 14, 15, and 16.
The furnace must be isolated from the gas supply piping system by
closing its individual external manual shutoff valve during any pressure
testing of the gas supply piping system at pressures equal to or less
than 1/2 psig (3.5 kPa).
Gas piping may be connected from either side of the furnace using any
of the gas pipe entry knockouts on both sides of the furnace. Refer to
Figure 5 dimensions.
FIGURE 14: Upflow Configuration (50-125 MBH Model Only)
FIGURE 15: Downflow Configuration (50-125 MBH Model Only)
CHECKING THE GAS PRESSURES
1.
The pressure ports on the gas valve are marked OUT P and IN
P.
2.
The manifold pressure must be taken at the port marked OUT P.
3.
The inlet gas supply pressure must be taken at the port marked
IN P.
4.
Using a 3/32” (0.2 cm) Allen wrench, loosen the set screw by
turning it 1 turn counter clockwise. DO NOT REMOVE THE
SET SCREW FROM THE PRESSURE PORT.
5.
Push one end the 3/8” (0.9 cm) ID flexible tubing over the pres-
sure port so that the body of the port is inside the tubing.
6.
Use a reducer connector to connect the 3/8” (0.9 cm) ID flexible
tube to a 1/4” (0.9 cm) ID flexible tube that is connected to a "U”
tube manometer or digital pressure measuring equipment.
IMPORTANT: The inlet gas pressure operating range table specifies
what the minimum and maximum gas line pressures must be for the
furnace to operate safely. The gas line pressure MUST BE a mini-
mum of:
•
7” W.C. (1.74 kPA) for Natural Gas
•
11” W.C. (2.74 kPA) for Propane (LP) Gas
in order to obtain the BTU input specified on the rating plate and/or
the nominal manifold pressure specified in these instructions and on
the rating plate.
TABLE 6: Inlet Gas Pressure Range
INLET GAS PRESSURE RANGE
Natural Gas
Propane (LP)
Minimum
4.5” W.C. (1.12 kPa)
8.0” W.C. (1.99 kPa)
Maximum
10.5” W.C. (2.61 kPa)
13.0” (3.24 kPa) W.C.
BLOWER
DOOR
SWITCH
ROLL-OUT
SWITCHES
BURNERS
HOT
SURFACE
IGNITOR
GAS
VALVE
PRESSURE
SWITCH
GAS
PIPE
GAS
SHUT-OFF
VALVE
ROLL-OUT
SWITCH
DIRT
LEG
VENT
BLOWER
FURNACE
CONTROL
BLOWER
DOOR
SWITCH
ROLL-OUT
SWITCHES
BURNERS
HOT
SURFACE
IGNITOR
GAS
VALVE
PRESSURE
SWITCH
VENT
VENT PIPE
TRANSITION
GAS
PIPE
3” DIAMETER
VENT PIPE
GAS
SHUT-OFF
VALVE
ROLL-OUT
SWITCH
DIRT LEG
VENT
BLOWER
FURNACE
CONTROL
FIGURE 16: Upflow/Horizontal Configuration (150 MBH Model Only)
FIGURE 17: Gas Piping
The gas valve body is a very thin casting that cannot take any
external pressure. Never apply a pipe wrench to the body of the gas
valve when installing piping. A wrench must be placed on the octa-
gon hub located on the gas inlet side of the valve. Placing a wrench
to the body of the gas valve will damage the valve causing improper
operation and/or the valve to leak.
BLOWER
DOOR
SWITCH
ROLL-OUT
SWITCHES
BURNERS
HOT
SURFACE
IGNITOR
GAS
VALVE
PRESSURE
SWITCH
GAS
PIPE
GAS
SHUT-OFF
VALVE
ROLL-OUT
SWITCH
DIRT
LEG
VENT
BLOWER
FURNACE
CONTROL
EXTERNAL MANUAL
SHUTOFF VALVE
TO GAS
SUPPLY
TO GAS
SUPPLY
GROUNDED JOINT UNION
MAY BE INSTALLED
INSIDE OR OUTSIDE UNIT.
DRIP
LEG
