supply/outlet or air conditioning coil casing (when used). When
installed on combustible material, supply-air duct attachment must
ONLY be connected to the accessory subbase, KGASB, or factory
approved air conditioning coil casing. DO NOT cut main furnace
casing to attach supply side air duct, humidifier, or other accesso-
ries. All accessories MUST be connected external to furnace
casing.
RETURN AIR CONNECTIONS
Never connect return-air ducts to the back of the furnace. A
failure to follow this warning can cause a fire, personal injury,
or death.
Downflow Furnaces
The return-air duct must be connected to return-air opening
(bottom inlet) as shown in Fig. 1. DO NOT cut into casing sides
(left or right). Side opening is permitted for only upflow and
certain horizontal furnaces. Bypass humidifier connections should
be made at ductwork or coil casing sides exterior to furnace. (See
Fig. 19.)
Upflow and Horizontal Furnaces
The return-air duct must be connected to bottom, sides (left or
right), or a combination of bottom and side(s) of main furnace
casing as shown in Fig. 1. Bypass humidifier may be attached into
unused side return air portion of the furnace casing. (See Fig. 18
and 20.)
Not all horizontal furnace models are approved for side return air
connections. (See Fig. 20.)
Step 6—Gas Piping
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. A failure to follow this
warning could result in fire, explosion, personal injury, or
death.
Use proper length of pipe to avoid stress on gas control
manifold. Failure to follow this warning could result in a gas
leak resulting in fire, explosion, personal injury, or death.
Gas piping must be installed in accordance with national and local
codes. Refer to current edition of NFGC in the U.S. and the
NSCNGPIC in Canada.
Installations must be made in accordance with all authorities
having jurisdiction. If possible, the gas supply line should be a
separate line running directly from meter to furnace.
Refer to Table 4 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
the action of propane gas.
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 serviced another gas appli-
ance. Black iron pipe shall be installed at the gas valve and
extend a minimum of 2 in. outside the furnace.
Connect gas pipe to furnace using a backup wrench to avoid
damaging gas controls.
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 gage connection, MUST be installed
immediately upstream of gas supply connection to furnace and
downstream of manual shutoff valve.
NOTE:
The gas valve inlet pressure tap connection is suitable to
use as test gage connection providing test pressure DOES NOT
exceed maximum 0.5 psig (14-in. wc) stated on gas control valve.
(See Fig. 50.)
Some installations require gas entry on right side of furnace (as
viewed in upflow). (See Fig. 21a.)
Install a sediment trap in riser leading to furnace as shown in Fig
21b. 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 exterior manual equip-
ment gas shutoff valve.
Piping should be pressure and leak tested in accordance with
NFGC in the United States or NSCNGPIC in Canada, local, and
national plumbing and gas codes before the furnace has been
connected. After all connections have been made, purge lines and
check for leakage at furnace prior to operating furnace.
Table 4—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 12.2 NFPA 54-2002.
→
Fig. 21a—Right Side Gas Entry Example
A02327
90
°
Elbow
2" Nipple
Street Elbow
Gas Valve
15
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