Step 7—Gas Piping
Gas piping must be installed in accordance with national and local
codes. Refer to current edition of NFGC in the United States.
Canadian installations must be made in accordance with NSCNG-
PIC and all authorities having jurisdiction.
Gas supply line should be a separate line running directly from
meter to furnace, if possible. Refer to Table 5 for recommended
gas pipe sizing.
Risers must be used to connect to furnace and to meter. Support all
gas piping with appropriate straps, hangers, etc. Use a minimum of
1 hanger every 6 ft. Joint compound (pipe dope) should be applied
sparingly and only to male threads of joints. Pipe dope must be
resistant to propane gas.
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in fire, explosion,
personal injury, or death.
- Connect gas pipe to furnace using a backup wrench to avoid
damaging gas controls.
- Gas valve shutoff switch MUST be facing forward or tilted
upward.
- Never purge a gas line into a combustion chamber. Never
test for gas leaks with an open flame. Use a commercially
available soap solution made specifically for the detection
of leaks to check all connections.
- Use proper length of pipe to avoid stress on gas control
manifold.
- If a flexible connector is required or allowed by authority
having jurisdiction, black iron pipe shall be installed at
furnace gas valve and extend a minimum of 2 in. outside
furnace casing.
-Protect gas valve from water and debris. Gas valve inlet
and/or inlet piping must remain capped until gas supply line
is permanently installed to protect the valve from moisture
and debris. Also, install a sediment trap in the gas supply
piping at the inlet to the gas valve.
Install a sediment trap in riser leading to furnace. Trap can be
installed by connecting a tee to riser leading to furnace so
straight-through section of tee is vertical. Then connect a capped
nipple into lower end of tee. Capped nipple should extend below
level of gas controls. Place a ground joint union between gas
control manifold and manual gas shutoff valve. (See Fig. 29.)
If local codes allow the use of a flexible gas appliance connector,
always use a new listed connector. Do not use a connector which
has previously served another gas appliance.
An accessible manual shutoff valve MUST be installed external to
furnace casing and within 6 ft of furnace. A 1/8-in. NPT plugged
tapping, accessible for test gauge connection, MUST be installed
immediately upstream of gas supply connection to furnace and
downstream of manual shutoff valve.
Piping should be pressure tested in accordance with NFGC, local
and national plumbing and gas codes before the furnace has been
connected. In Canada, refer to current edition of NSCNGPIC. If
the pressure exceeds 0.5 psig (14-in. wc), gas supply pipe must be
disconnected from the furnace and capped before pressure test. If
test pressure is equal to or less than 0.5 psig (14-in. wc), turn off
electric shutoff switch located on furnace gas valve and accessible
manual shutoff valve before test. After all connections have been
made, purge lines and check for leakage.
FIRE OR EXPLOSION HAZARD
Failure to follow this warning exactly could result in serious
injury, death, or property damage.
Never test for gas leaks with an open flame. Use a commer-
cially available soap solution made specifically for the
detection of leaks to check all connections. A fire or explo-
sion could result causing property damage, personal injury or
loss of life.
Gas line grommet (factory-supplied loose parts bag) should be
used when installing gas piping. Gas line entry hole filler plug
should be installed in unused gas line entry hole. (See Fig. 30.)
NOTE:
The gas valve inlet pressure tap connection is suitable to
use as test gauge connection providing test pressure DOES NOT
exceed maximum 0.5 psig (14-in. wc) stated on gas valve. (See
Fig. 51.)
The gas supply pressure shall be within the maximum and
minimum inlet supply pressures marked on the rating plate with
the furnace burners ON at HI-HEAT and OFF.
Table 5—Maximum Capacity of Pipe*
NOMINAL
IRON
PIPE
SIZE
(IN.)
INTERNAL
DIAMETER
(IN.)
LENGTH OF PIPE (FT)
10
20
30
40
50
1/2
0.622
175
120
97
82
73
3/4
0.824
360
250
200
170
151
1
1.049
680
465
375
320
285
1-1/4
1.380
1400
950
770
660
580
1-1/2
1.610
2100
1460
1180
990
900
* Cubic ft of gas per hr. for gas pressures of 0.5 psig (14–in. wc) or less and
a pressure drop of 0.5–in wc (based on a 0.60 specific gravity gas).
Ref: Table 9.2 NFGC.
Fig. 29—Typical Gas Pipe Arrangement
A93324
UNION
SEDIMENT
TRAP
MANUAL
SHUTOFF
VALVE
(REQUIRED)
GAS
SUPPLY
24
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