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IV-HEATING SYSTEM SERVICE CHECKS
A-CSA Certification
All units are CSA design certified without modifications.
Refer to the SL297UHNV Installation Instruction.
B-Gas Piping
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet.
WARNING
Do not over torque (800 in-lbs) or under torque (350
in-lbs) when attaching the gas piping to the gas
valve.
Gas supply piping should not allow more than 0.5”W.C. drop
in pressure between gas meter and unit. Supply gas pipe
must not be smaller than unit gas connection.
Compounds used on gas piping threaded joints should be
resistant to action of liquefied petroleum gases.
C-Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shut‐off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas valve must be dis
connected and isolated. Gas valves can be damaged if
subjected to more than 0.5 psig (14” W.C.). See figure 45
.
If
the pressure is greater than 0.5psig (14”W.C.), use the
manual shut-off valve before pressure testing to isolate fur
nace from gas supply.
FIGURE 45
GAS PIPING TEST PROCEDURE
Isolate Gas Valve
Manual Main Shut-Off Valve Will
Not Hold Normal Test Pressure
1/8” N.P.T.
Plugged Tap
Cap
When checking piping connections for gas leaks, use pre
ferred means. Kitchen detergents can cause harmful corro
sion on various metals used in gas piping. Use of a specialty
Gas Leak Detector is strongly recommended. It is available
through Lennox under part number 31B2001. See Corp.
8411-L10, for further details.
Do not use matches, candles, flame or any other
source of ignition to check for gas leaks.
D-Testing Gas Supply Pressure
A threaded plug on the inlet side of the gas valve provides
access to the supply pressure tap. Remove the threaded
plug, install a field-provided barbed fitting and connect a
manometer to measure supply pressure. Replace the
threaded plug after measurements have been taken. See
table 26 for supply line pressure.
E- Proper Gas Flow (Approximate)
Furnace should operate at least 5 minutes before check
ing gas flow. Determine time in seconds for
two
revolu
tions of gas through the meter. (Two revolutions assures a
more accurate time.)
Divide by two
and compare to time
in table 25 below. If manifold pressure matches table 25
and rate is incorrect, check gas orifices for proper size and
restriction.
NOTE- To obtain accurate reading, shut off all other gas
appliances connected to meter.
TABLE 25
GAS METER CLOCKING CHART
SL297
Model
Seconds for One Revolution
Natural
LP/Propane
1 cu ft
Dial
2 cu ft
Dial
1 cu ft
Dia
2 cu ft
Dial
040
90
180
N/A
N/A
060
60
120
150
300
080
45
90
112
224
Natural-1000 btu/cu f LP/Propane - 2500 btu/cuf
TABLE 26
Manifold and Supply Line and LP Conversion Kits*
Unit
Fue
l
Supply Line Pressure
in. w.g.
Min
Max
All Sizes
Nat
4.5
10.5
-040
LP
N/A
N/A
-060*
11.0
13.0
-080*
