Lennox EL280UHE Series Unit Information page 26

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 19. 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.
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT-OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14"W.C.)
GAS VALVE
FIGURE 19
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. See table 14 for
supply line pressure. Replace the threaded plug after mea­
surements have been taken.
E-Check Manifold Pressure
After line pressure has been checked and adjusted, check
manifold pressure. Checks of manifold pressure are made
as verification of proper regulator adjustment. Manifold pres­
sure for the EL280UHE(X) can be measured at any time the
gas valve is open and is supplying gas to the unit.
1/8 NPT PLUG
CAP
IMPORTANT
For safety, connect a shut‐off valve between the ma­
nometer and the gas tap to permit shut off of gas
pressure to the manometer.
The gas valve is factory set and should not require adjust­
ment. All gas valves are factory regulated.
Manifold Adjustment Procedure:
NOTE - Pressure test adapter kit (10L34) is available from
Lennox to facilitate manifold pressure measurement.
1 - Connect test gauge to manifold pressure post (figure
18) on gas valve.
2 - Ignite unit on low fire and let run for 5 minutes to allow
for steady state conditions.
3 - After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in table
14.
4 - If necessary, make adjustments. Figure 18 show loca­
tion of high fire and low fire adjustment screw.
5 - Repeat steps 2, 3 and 4 on high fire.
6 - Shut unit off and remove manometer as soon as an ac­
curate reading has been obtained. Take care to re­
place pressure tap plug.
7 - Start unit and perform leak check. Seal leaks if found.
F- 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 12 below. If manifold pressure matches table 14
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.
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
Input
1 cu ft
Dial
-045 80
-70 55
-90 41
-110 33
Natural-1000 btu/cu ft
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
Page 26
TABLE 12
LP
2 cu ft 1 cu ft 2 cu ft
Dial Dial
160 200
110 136
82 102
66 82
LP-2500 btu/cu ft
DIAL
400
272
204
164