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RP-HRPD-IOM (07-22) 132210-B
ADJUSTMENTS
Measure and Adjust Manifold (Outlet) Gas Pressure
Measuring manifold gas pressure cannot be done until the heater is in operation (refer to
section) .
• For natural gas:
When the heater leaves the factory, the combination valve is set so that the outlet gas pressure
of a single-stage valve or high fire of a two-stage valve is regulated to 3 .5 IN WC . Low fire on a two-stage valve
is set to 1 .8 IN WC . Inlet supply pressure to the valve must be a minimum of 5 IN WC or as noted on the rating
plate and a maximum of 14 IN WC .
NOTE: Always check the rating plate for minimum gas supply pressure.
• Minimum natural gas supply pressure:
Requirements vary based on size of burner and the gas control option .
Most units require a minimum of 5 IN WC natural gas as stated above, but sizes 350 and 400 with electronic
modulation require a minimum of 6 IN WC natural gas supply pressure . Sizes 300 and 350 with mechanical
modulation require 7 IN WC .
• For propane gas:
When the heater leaves the factory, the combination valve is set so that the outlet gas pressure
of a single-stage valve or high fire of a two-stage valve is 10 IN WC . Low fire on a two-stage valve is set to 5 IN
WC . Inlet pressure to the valve must be a minimum of 11 IN WC and a maximum of 14 IN WC .
⚠ WARNING ⚠
• Manifold gas pressure must never exceed 3.5 IN WC for natural gas or 10 IN WC for propane gas.
• Before attempting to measure or adjust manifold gas pressure, the inlet (supply) pressure must
be within the specified range for the gas being used, both when the heater is in operation and
when it is on standby. Incorrect inlet pressure could cause excessive manifold gas pressure
immediately or at some future time.
NOTE: A manometer (fluid-filled gauge) is recommended rather than a spring-type gauge due to
the difficulty of maintaining calibration of a spring-type gauge.
1 . With the manual valve (on the combination valve) positioned to prevent flow to the main burners, connect a
manometer to the 1/8-inch pipe outlet pressure tap in the valve .
2 . Open the valve and operate the heater . Measure the gas pressure to the manifold . To measure the low-stage
pressure on units equipped with a two-stage valve, disconnect the wire from the HI terminal on the valve . Be
sure to reconnect the wire .
⚠ CAUTION ⚠
DO NOT bottom out the gas valve regulator screw. This can result in excessive overfire and heat
exchanger failure due to unregulated manifold pressure.
3 . Normally, adjustments to the factory-preset regulator should not be necessary . If adjustment is necessary,
set pressure to correct settings by turning the regulator screw IN (clockwise) to increase pressure or OUT
(counterclockwise) to decrease pressure . Consult the valve manufacturer’s literature provided with the furnace
for more detailed information .
High Elevation (>2,000 Feet/609 Meters) Installations
NOTES:
• High elevation (>2,000 feet/609 meters) application with this unit depends on the installation
elevation and the heating value of the gas. At high elevations, the heating value of natural gas is
always lower than the heating value at sea level.
• Deration is necessary to compensate for low atmospheric pressure at high elevations. Generally
this will require obtaining the gas heating value from the local gas utility and replacing the burner
orifices.
