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19
Return Air
Connections
FIRE HAZARD
A failure to follow this warning could cause personal injury,
death and/or property damage.
Never connect return--air ducts to the back of the furnace.
Follow instructions below.
!
WARNING
Downflow Furnaces
The return--air duct must be connected to return--air opening
(bottom inlet) as shown in Fig. 3. 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. 3. Bypass humidifier may be attached
into unused return air side of the furnace casing. (See Fig. 18 and
20.) Not all horizontal furnace models are approved for side
return air connections. (See Fig. 20.)
GAS
PIPING
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
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.
!
WARNING
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
Use proper length of pipe to avoid stress on gas control
manifold and a gas leak.
!
WARNING
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
Gas valve inlet and/or inlet pipe 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.
!
WARNING
Gas piping must be installed in accordance with national and
local codes. Refer to current edition of NFGC in the U.S.
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.
NOTE: In the state of Massachusetts:
1. Gas supply connections MUST be performed by a li-
censed plumber or gas fitter.
2. When flexible connectors are used, the maximum length
shall not exceed 36 in. (915 mm).
3. When lever handle type manual equipment shutoff valves
are used, they shall be T--handle valves.
4. The use of copper tubing for gas piping is NOT approved
by the state of Massachusetts.
Refer to Table 6 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. (1.8 M). 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.
Table 6 – Maximum Capacity of Pipe
NOMINAL
IRON PIPE
SIZE
IN. (MM)
INTERNAL
DIA.
IN. (MM)
LENGTH OF PIPE --- FT (M)
10
(3.0)
20
(6.0)
30
(9.1)
40
(12.1)
50
(15.2)
1/2 (12.7) 0.622(158) 175 120 97 82 73
3/4 (19.0) 0.824 (20.9) 360 250 200 170 151
1 ( 25.4) 1.049 (26.6) 680 465 375 320 285
1-1/4
(31.8)
1.380 (35.0) 1400 950 770 660 580
1-1/2
(38.1)
1.610 (40.9) 2100 1460 1180 990 900
* C ubic ft of gas p er hr for gas pressures of 0.5 psig (14---In. W.C.) or less and
a pressure drop of 0.5---In. W .C. (based on a 0.60 specific g ravity gas). Ref:
Table 6 and 9.2 NFGC.
FIRE OR EXPLOSION HAZARD
A failure to follow this warning could result in personal
injury, death, and/or property damage.
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. Black iron pipe shall be installed at the furnace
gas control valve and extend a minimum of 2--in. (51 mm)
outside the furnace.
!
WARNING
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in furnace damage.
Connect gas pipe to furnace using a backup wrench to
avoid damaging gas controls and burner misalignment.
CAUTION
!
An accessible manual equipment shutoff valve MUST be
installed external to furnace casing and within 6 ft. (1.8 M) of
furnace. A 1/8--in. (3 mm) NPT plugged tapping, accessible for
test gauge connection, MUST be installed immediately upstream
of gas supply connection to furnace and downstream of manual
equipment shutoff valve.
NOTE: The furnace gas control 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.
W.C.) stated on gas control valve. (See Fig. 50.)
Some installations require gas entry on right side of furnace (as
viewed in upflow). (See Fig. 21.)
Install a sediment trap in riser leading to furnace as shown in Fig.
22. Connect a capped nipple into lower end of tee. Capped nipple
315AAV