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Gas Pressure Adjustment
Gas Flow (Approximate)
GAS METER CLOCKING CHART
Seconds for One Revolution
Natural
Unit
1 cu ft
Dial
−045
80
−070
55
−090
41
−110
33
−135
27
Natural−1000 btu/cu ft
NOTE: To obtain accurate reading, shut off all other gas
appliances connected to meter.
Furnace should operate at least 5 minutes before checking
gas flow. Determine time in seconds for two revolutions of
gas through the meter. (Two revolutions assures a more
accurate time.)
Divide by two and compare to time in
Table 11. If manifold pressure matches Table 12 and rate
is incorrect, check gas orifices for proper size and restriction.
Remove temporary gas meter if installed.
Supply Pressure Measurement
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.
Manifold Pressure Measurement
1. Remove the threaded plug from the outlet side of the
gas valve and install a field provided barbed fitting.
Connect to a manometer to measure manifold pressure.
2. Start unit and allow 5 minutes for unit to reach steady
state.
3. While waiting for the unit to stabilize, observe the flame.
Flame should be stable and should not lift from burner.
Natural gas should burn blue.
4. After allowing unit to stabilize for 5 minutes, record
manifold pressure and compare to value given in
Table 12.
NOTE: Shut unit off and remove manometer as soon as
an accurate reading has been obtained. Take care to remove
barbed fitting and replace threaded plug.
Page 36 of 48
LP
2 cu ft
1 cu ft
Dial
Dial
160
200
110
136
82
102
66
82
54
68
LP−2500 btu/cu ft
TABLE 11
Supply Line and Manifold Pressure (inches w.c.)
Unit
All
2 cu ft
All
DIAL
400
272
NOTE:
A natural to L.P. propane gas changeover kit is necessary
204
to convert this unit. Refer to the changeover kit installation
164
instruction for the conversion procedure.
136
Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Take combustion sample beyond the flue outlet
and compare to the tables below. The maximum carbon
monoxide reading should not exceed 50 ppm.
The maximum carbon monoxide reading should not exceed 50 ppm.
High Altitude Information
NOTE: In Canada, certification for installations at elevations
over 4500 feet (1372 m) is the jurisdiction of local authorities.
The furnace requires no manifold pressure adjustments for
operation at altitudes up to 10,000 feet (3048 m) above sea
level. Units installed at altitudes of 4501 - 10,000 feet (1373
to 3048 m) require a pressure switch change which can be
ordered separately. Table 14 lists conversion kit and
pressure switch requirements at varying altitudes.
The combustion air pressure switch is factory-set and
requires no adjustment.
Issue 1109
Manifold
Fuel
Pressure
Nat. Gas
3.5
L.P. Gas
10.0
TABLE 12
Unit
CO
%
2
For Nat
All
7.2 − 7.9
TABLE 13
Line Pressure
4.5 − 10.5
11.0 − 13.0
CO
%
2
For L.P.
8.6 − 9.3
506725-01
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