14
GAS PIPING
NOTICE: See General Safety Information section for
English/Metric unit conversion factors.
NOTICE: If more than one duct furnace is to be served
by the same piping arrangement, the total cu. ft./hr.
input and length of pipe must be considered.
NOTICE: If the duct furnace is to be fi red with LP
gas, consult your local LP gas dealer for pipe size
information.
NOTICE: Heater installation for use with propane
(bottled) gas must be made by a qualifi ed LP gas
dealer or installer. He will insure that proper joint
compounds are used for making pipe connections;
that air is purged from lines; that a thorough test is
made for leaks before operating the heater; and that
it is properly connected to the propane gas supply
system.
Before any connection is made to the existing line
supplying other gas appliances, contact the local gas
company to make sure that the existing line is of adequate
size to handle the combined load.
1. Determine the required Cu. Ft. / Hr. by dividing the rated heater input by 1000. For SI / Metric measurements: Convert unit Btu. / Hr. to
kilowatts. Multiply the units input (kW) by 0.0965 to determine Cubic Meters / Hour. 2. FOR NATURAL GAS: Select the pipe size directly
from the table. 3. FOR PROPANE GAS: Multiply the Cu. Ft. / Hr. (Cubic Meters per Hour) value by 0.633; then use the table. 4. Refer to
the metric conversion factors listed in General Safety section for more SI unit measurements/conversions.
To avoid damage or possible
personal injury, do not connect gas piping to this
unit until a supply line pressure/leak test has
been completed. Connecting the unit before
completing the pressure/leak test may damage
the gas valve and result in fi re hazard.
Do not rely on a shut-off valve to
isolate the unit while conducting gas pressure/
leak tests. These valves may not be completely
shut off, exposing the gas valve to excessive
pressure and damages.
PIPE SIZING
To provide adequate gas pressure to the gas duct furnace,
size the gas piping as follows:
1. Find cu. ft./hr. by using the following formula:
Input
Cu. ft./hr. =
BTU/Cu. ft.
2. Refer to table 4. Match “Length of Pipe in Feet” with
appropriate “Gas Input - Cu. Ft./Hr.” fi gure. This fi gure
can then be matched to the pipe size at the top of the
column.
Example:
It is determined that a 67 foot (20.4m) run of gas pipe is
required to connect a 200 MBTU gas duct furnace to a
1,000 BTU/cu. ft. (0.29kW) natural gas supply.
200,000 BTU/Hr
1,000 BTU/Cu. ft.
= 200 Cu. ft./hr.
Using Table 4, a 1 inch pipe is needed.
Maximum Capacity of Pipe in Cubic Feet of Gas per Hour (Cubic Meters per Hour) for Gas Pressures of 0.5 psig (3.5 kPa) or Less,
and a Pressure Drop of 0.5 Inch Water Column (124.4 Pa)
(Based on a 0.60 Specifi c Gravity Gas)
Nominal
Iron
Internal
Length of Pipe, Feet (meters)
Pipe
Size
Dia. 10 20 30 40 50 60 70 80 90 100
125
150
175
200
in.
in.
(3.0) (6.1) (9.1) (12.2) (15.2) (18.3) (21.3) (24.4) (27.4) (30.5) (38.1) (45.7) (53.3) (61.0)
1/2
0.622
175
120 97 82 73 66 61 57 53 50 44 40 37 35
(4.96) (3.40) (2.75) (2.32) (2.07) (1.87) (1.73) (1.61) (1.50) (1.42) (1.25) (1.13) (1.05) (0.99)
3/4 0.824 360 250 200 170 151 138 125 118 110 103 93 84 77 72
(10.2) (7.08) (5.66) (4.81) (4.28) (3.91) (3.54) (3.34) (3.11) (2.92) (2.63) (2.38) (2.18) (2.04)
1 1.049 680 465 375 320 285 260 240 220 205 195 175 160 145 135
(19.3) (13.2) (10.6) (9.06) (8.07) (7.36) (6.80) (6.23) (5.80) (5.52) (4.96) (4.53) (4.11) (3.82)
1
1/4
1.380
1400 950 770 660 580 530 490 460 430 400 360 325 300 280
(39.6) (26.9) (21.8) (18.7) (16.4) (15.0) (13.9) (13.0) (12.2) (11.3) (10.2) (9.20) (8.50) (7.93)
1
1/2
1.610
2100
1460
1180 990 900 810 750 690 650 620 550 500 460 430
(59.5) (41.3) (33.4) (28.0) (25.5) (22.9) (21.2) (19.5) (18.4) (17.6) (15.6) (14.2) (13.0) (12.2)
2 2.067 3950 2750 2200 1900 1680 1520 1400 1300 1220 1150 1020 950 850 800
(112) (77.9) (62.3) (53.8) (47.6) (43.0) (39.6) (36.8) (34.5) (32.6) (28.9) (26.9) (24.1) (22.7)
2
1/2 2.469 6300 4350 3520 3000 2650 2400 2250 2050 1950 1850 1650 1500 1370 1280
(178) (123) (99.7) (85.0) (75.0) (68.0) (63.7) (58.0) (55.2) (52.4) (46.7) (42.5) (38.8) (36.2)
3 3.068 11000 7700 6250 5300 4750 4300 3900 3700 3450 3250 2950 2650 2450 2280
(311) (218) (177) (150) (135) (122) (110) (105) (97.7) (92.0) (83.5) (75.0) (69.4) (64.6)
4 4.026 23000
15800
12800
10900 9700 8800 8100 7500 7200 6700 6000 5500 5000 4600
(651) (447) (362) (309) (275) (249) (229) (212) (204) (190) (170) (156) (142) (130)
Table 4 - Gas Pipe Size
