Setting Gas Pressure - Rheem RGPE series Installation Instructions Manual

SETTING GAS PRESSURE

The maximum gas supply pressure to
the furnace should be 10.5" w.c. natur-
al gas, or 13" w.c. LP gas. The mini-
mum supply gas pressure to the gas
valve should be 5" w.c. natural gas or
11" w.c. LP gas. A properly calibrated
manometer is required for accurate gas
pressure measurements.
Supply Gas Pressure Measurement.
A line pressure tap is on the inlet side
of the gas valve.
1. With gas shut off to the furnace at
the manual gas valve outside the
unit, remove the input pressure
tap plug.
2. Connect a U-Tube manometer to
the pressure tap.
3. Turn on the gas supply and oper-
ate the furnace and all other gas-
fired units on the same gas line as
the furnace.
4. Adjust the line gas pressure to
supply:
A. 5" - 10.5" w.c. for natural gas.
B. 11" - 13" w.c. for LP gas.
5. Shut off the gas at the manual gas
valve and remove the
U-Tube manometer.
6. Replace the pressure tap plug.
7. Turn gas on, and check for leaks.
NATURAL GAS:
If the supply gas line pressure is above
the operating range, install an in-line
gas regulator to the furnace. If supply
gas line pressure is below the operat-
ing range, either remove any restric-
tions in the gas supply piping or
enlarge the gas pipe. See Table 2.
LP GAS:
If the supply gas line pressure is above
the operating range, have the LP sup-
plier reduce the line pressure at the
regulator. If supply gas line pressure is
below operating range, have the LP
supplier adjust the line pressure at the
regulator. See Table 3.
NOTE: Depending on the amount of
LP vapor and the outdoor ambient tem-
perature, the LP storage tank may
require supplemental heat to maintain
proper pressure levels. Ensure LP stor-
age tank does not drop below 15%
capacity during heating season.
FIGURE 16
TYPICAL HOSE CONNECTION TO LINE PRESSURE TAP
TABLE 2
NATURAL GAS PIPE CAPACITY TABLE (CU. FT./HR.)
Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific
gravity of 0.60 (natural gas).
Nominal
Iron Pipe
Size, Inches 10 20
1/2 132 92
3/4 278 190
1 520 350
1-1/4 1,050 730
1-1/2 1,600 1,100
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per
hour required for the gas input rating of the furnace. By formula:
Cu. Ft. Per Hr. Required
The gas input of the furnace is marked on the furnace rating plate. The heating value of the gas (BTU/FT3) may be
determined by consulting the local natural gas utility or the LP gas supplier.
TABLE 3
LP GAS PIPE CAPACITY TABLE (CU. FT./HR.)
Maximum capacity of pipe in thousands of BTU per hour of undiluted liquefied petroleum gases (at 11 inches water
column inlet pressure).
(Based on a Pressure Drop of 0.5 Inch Water Column)
Nominal
Iron Pipe
Size, Inches 10 20 30
1/2 275 189 152
3/4 567 393 315
1 1,071 732 590
1-1/4 2,205 1,496 1,212
1-1/2 3,307 2,299 1,858
2 6,221 4,331 3,465
Example (LP): Input BTU requirement of unit, 150,000
Equivalent length of pipe, 60 ft. = 3/4" IPS required.
Length of Pipe, Feet
30 40 50
73 63 56
152 130 115
285 245 215
590 500 440
890 760 670
Gas Input of Furnace (BTU/HR)
=
Heating Value of Gas (BTU/FT3)
Length of Pipe, Feet
40 50 60 70 80
129 114 103 96 89
267 237 217 196 182
504 448 409 378 346
1,039 913 834 771 724
1,559 1,417 1,275 1,181 1,086 1,023
2,992 2,646 2,394 2,205 2,047 1,921 1,811 1,606 1,496
60 70 80
50 46 43
105 96 90
195 180 170
400 370 350
610 560 530
90 100 125 150
83 78 69 63
173 162 146 132
322 307 275 252
677 630 567 511
976 866 787
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