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506501-01 Page 39 of 48Issue 1031
Gas Pressure Adjustment
Gas Flow (Approximate)
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 8. If manifold pressure matches Table 9 and rate is
incorrect, check gas orifices for proper size and restriction.
Remove temporary gas meter if installed.
NOTE: To obtain accurate reading, shut off all other gas
appliances connected to meter.
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.
For proper furnace operation the minimum gas supply
pressure is 5" w.c and the maximum gas supply pressure is
13" w.c for natural gas. The minimum gas supply pressure
is 10" w.c. and the maximum gas supply pressure is 13"
w.c. for LP/propane gas.
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
9.
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.
High Altitude Information
NOTE: In Canada, certification for installations at elevations
over 4500 feet (1372 m) is the jurisdiction of local authorities.
The manifold pressure may require adjustment to ensure
proper operation at higher altitudes. Refer to Table 9 for
proper manifold pressure settings at varying altitudes. Table
10 lists required pressure switch changes and conversion
kits at varying altitudes.
The combustion air pressure switches are factory set and
require no adjustment.
Manifold Pressure (Outlet) Inches w.c.
NOTE: A natural to L.P./propane gas changeover kit is
necessary to convert this unit. Refer to the literature kit
installation instruction for the conversion procedure.
Table 9
Conversion Kit and Pressure Switch Requirements at Varying Altitudes
Pressure switch is factory set. No adjustment necessary. All models use the factory installed pressure switch from 0-4500 feet (0-1370 m).
Table 10
Table 8