Rheem RGPK Installation Instructions Manual page 17

SETTING GAS PRESSURE
The maximum gas supply pressure
to the furnace should be 10.5
natural gas, or 13 w.c. LP gas. The
minimum supply gas pressure to the
gas valve should be 5" w.c. natural gas
or 11" w.c. LP gas. A properly
calibrated U-Tube manometer is
required for accurate gas pressure
measurements.
Supply Gas Pressure Measurement.
A line pressure tap is on the input 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
operate the furnace and all other
gas-fired units on the same gas
line as the furnace.
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
1/2 132
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
1/2 275
3/4 567
1 1,071
1-1/4 2,205
1-1/2 3,307
2 6,221
Example (LP): Input BTU requirement of unit, 150,000
4. Note or adjust the line gas
w.c.
pressure to give:
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
before turning on the gas.
If the supply gas line pressure is above
these ranges, install an in-line gas
regulator to the furnace for natural gas
units. With LP gas, have the LP
supplier reduce the line pressure at the
regulator.
If supply gas line pressure is below
these ranges, either remove any
restrictions in the gas supply piping or
enlarge the gas pipe. See Tables 2 and
3. With LP gas, have the LP supplier
adjust the line pressure at the regulator.
Length of Pipe, Feet
20 30 40 50
92 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)
10 20 30 40
189 152 129
393 315 267
732 590 504
1,496 1,212 1,039
2,299 1,858 1,559 1,417
4,331 3,465 2,992 2,646
Equivalent length of pipe, 60 ft. = 3/4" IPS required.
60 70 80
50 46 43
105 96 90
195 180 170
400 370 350
610 560 530
Length of Pipe, Feet
50 60 70 80
114 103 96 89
237 217 196 182 173
448 409 378 346 322
913 834 771 724 677
1,275 1,181 1,086 1,023
2,394 2,205 2,047 1,921 1,811 1,606 1,496
WARNING
!
NEVER PURGE A GAS LINE INTO
THE COMBUSTION CHAMBER.
NEVER USE MATCHES, FLAME OR
ANY IGNITION SOURCE FOR
CHECKING LEAKAGE. FAILURE TO
FOLLOW THIS WARNING CAN
CAUSE AN EXPLOSION OR FIRE
RESULTING IN PROPERTY
DAMAGE, PERSONAL INJURY OR
DEATH.
To check for gas leakage, use an
approved chloride-free soap and water
solution, an electronic combustible gas
detector (see Figure 13), or other
approved method.
FIGURE 13
ELECTRONIC COMBUSTIBLE
GAS DETECTOR
90 100 125 150
83 78 69 63
162 146 132
307 275 252
630 567 511
976 866 787
17