Timing Diagram; Adjusting Or Checking Furnace Input . 91 24 Setting Input Rate - Rheem R95P Installation Instructions Manual

TABLE 16

TIMING DIAGRAM

ST-A1194-27-X0
The maximum gas supply pressure to the furnace should
be 7" w.c. for natural gas. The minimum gas supply pres-
sure for purposes of input adjustment to the furnace should
be 5" w.c.
A calibrated manometer is required for accurate gas pres-
sure readings.
The manifold pressure should be set at 3.5" w.c. for natural
gas. Only small variations in the gas flow should be made
by means of the pressure regulator adjustment. In no case
should the final manifold pressure vary more than plus or
minus 0.3" w.c. from the above- specified pressures. To
adjust the pressure regulator, remove the regulator cap
and turn the adjustment screw clockwise to increase pres-
sure or counterclockwise to decrease pressure. Then re-
place the regulator cap securely. Any necessary major
changes in the gas flow rate should be made by changing
the size of the burner orifices.
The furnace is shipped from the factory with #51 orifices.
They are sized for natural gas having a heating value of
1100 BTU/cu. ft. and a specific gravity of .60.
Since heating values vary geo-graphically, the manifold
pressure and/or gas orifice size may need to be changed
to adjust the furnace to its nameplate input. Consult the
local gas utility to obtain the yearly average heating value
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To change orifice spuds, shut off the manual gas valve and
remove the gas manifold. On LP gas furnaces, the LP gas
supply pressure must be set between 11" and 14" w.c. by
means of the tank or branch supply regulators. The fur-
nace manifold pressure should be set at 10" w.c. at the gas
control valve. For elevations up to 2,000 feet, rating plate
input ratings apply. For high altitudes (elevations over
2,000 ft.), see conversion kit index for derating and orifice
spud sizes.
Checking furnace input is important to prevent over firing
beyond its design-rated input. NEVER SET INPUT ABOVE
THAT SHOWN ON THE RATING PLATE. Use the follow-
ing table or formula to determine input rate. Start the fur-
nace and measure the time required to burn one cubic foot
of gas. Prior to checking the furnace input, make certain
that all other gas appliances are shut off, with the excep-
tion of pilot burners. Time the meter with only the furnace
in operation.
and orifice size required to fire each individual burner at
14,000 BTU/HR.
NOTE: Refer to the High Altitude Section of this manual
and the National Fuel Gas Code for high altitude rate ad-
justment above 2,000 ft.
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