Reznor FT Unit Installation Manual - Manual (Page 11)

Form RZ-NA-I-FT, Page 10
12. Gas Pressures (cont'd)
Sizing a Gas
Supply Line
Manifold or Orifice Pressure Settings
Measuring manifold gas pressure cannot be done until the heater is in
operation. It is included in the steps of the "Check-Test-Start" proce-
dure in Paragraph 21. The following warnings and instructions apply.
WARNING: Manifold gas pressure must never exceed
3.5" w.c. for natural gas and 10" w.c. for propane
gas.
For Natural Gas:
When the heater leaves the factory, the combination
gas valve is set so that the manifold gas pressure is regulated to 3.5"
w.c. Inlet supply pressure to the valve for natural gas must be a mini-
mum of 5" w.c. or as noted on the rating plate and a maximum of 14"
w.c.
For Propane Gas:
When the heater leaves the factory, the combina-
tion gas valve is set so that the manifold gas pressure is regulated to
10" w.c. Inlet supply pressure to the valve for propane gas must be a
minimum of 11" w.c. and a maximum of 14" w.c.
Before attempting to measure or adjust manifold gas pressure, the inlet
supply pressure must be within the specified range both when the heater
is in operation and on standby. Incorrect inlet pressure could cause
excessive manifold gas pressure immediately or at some future time. If
natural gas supply pressure is too high, install a regulator in the supply
line before it reaches the heater. If natural gas supply pressure is too
low, contact your gas supplier.
From Gas
Supply
From Gas
Supply
6” Drip Leg
NOTE: Connections
shown are by the installer.
To Controls
Manual
Gas Valve
Immediately upstream of the gas
supply connection, install a manual
shutoff valve with a 1/8” NPT
plugged tap accessible for test
gauge connection.
Ground Joint Union
Figure 8 -
Supply Piping
Connection
Instructions on How to Check Manifold
Pressure (can only be done after heater is
installed):
1)
With the manual valve positioned to prevent flow to the main burn-
ers, connect a manometer to the 1/8" pipe outlet pressure tap in the
valve. NOTE: A manometer (fluid-filled gauge) is recommended rather
than a spring type gauge due to the difficulty of maintaining calibra-
tion of a spring type gauge.
2)
Open the valve and operate the heater. Measure the gas pressure to
the manifold. Normally adjustments should not be necessary to the
factory preset regulator.
If adjustment is necessary, set pressure to correct settings by turning
the regulator screw IN (clockwise) to increase pressure. Turn regulator
screw OUT (counterclockwise) to decrease pressure.
Derating by Manifold Pressure Adjustment for
High Altitude Operation
If the heater is being installed above 2000 ft (610M) and it was deter-
mined in Paragraph 4 that derating by manifold pressure adjustment is
permissible, follow the instructions below.
Instructions for Derating a Heater by Adjusting Manifold
Pressure (The heater must have a single-stage gas valve
and must be factory-equipped for sea level operation.)
1. Check the rating plate to be certain that the heater is equipped for
sea level operation. Do not attempt to derate by manifold gas pres-
sure adjustment if the heater is factory equipped for high alti-
tude. Do not attempt to adjust manifold pressure on heaters
equipped with two stage gas valves.
2. Determine the required manifold pressure for the elevation where
the heater will be operating. If unsure of the elevation, contact the
local gas supplier.
Manifold Pressure Settings by Elevation
Altitude Natural Gas Propane Gas
Feet Meters (inches W.C.) (inches W.C.)
0- 2000 1-610 3.5 10.0
2001-3000 611-915 2.8 7.7
3001-4000 916-1220 2.5 7.1
4001-5000 1221-1525 2.3 6.4
5001-6000 1526-1830 2.1 5.8
6001-7000 1831-2135 1.9 5.2
7001-8000 2136-2440 1.7 4.6
8001-9000 2441-2745 1.5 4.1
Capacity of Piping
Cubic Feet per Hour based on 0.3" w.c. Pressure Drop
Specific Gravity for Natural Gas -- 0.6 (Natural Gas -- 1000 BTU/Cubic Ft)
Specific Gravity for Propane Gas -- 1.6 (Propane Gas -- 2550 BTU/Cubic Ft)
Length Diameter of Pipe
of 1/2" 3/4" 1" 1-1/4" 1-1/2" 2"
Pipe Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane Natural Propane
20' 92 56 190 116 350 214 730 445 1100 671 2100 1281
30' 73 45 152 93 285 174 590 360 890 543 1650 1007
40' 63 38 130 79 245 149 500 305 760 464 1450 885
50' 56 34 115 70 215 131 440 268 670 409 1270 775
60' 50 31 105 64 195 119 400 244 610 372 1105 674
70' 46 28 96 59 180 110 370 226 560 342 1050 641
80' 43 26 90 55 170 104 350 214 530 323 990 604
90' 40 24 84 51 160 98 320 195 490 299 930 567
100' 38 23 79 48 150 92 305 186 460 281 870 531
125' 34 21 72 44 130 79 275 168 410 250 780 476
150' 31 19 64 39 120 73 250 153 380 232 710 433
175' 28 17 59 36 110 67 225 137 350 214 650 397
200' 26 16 55 34 100 61 210 128 320 195 610 372
Note: When sizing supply lines, consider possibilities of future expansion and increased requirements.
Refer to National Fuel Gas Code for additional information on line sizing.