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IMPORTANT: Gas pressure to appliance controls must never
exceed 13.5 in. wg (1/2 psig).
The individual duct furnace inlet gas supply pipe connection size
is 3/4 in. NPT for gas inputs up to 400,000 Btuh and
1 in. NPT for gas inputs between 401,000 and 600,000 Btuh for all
control systems.
The duct furnace gas piping was leak tested prior to shipping the
furnace. However, during shipping and installation connections
may have loosened. Check for leaks using a soap solution and cor-
rect any leaks before placing furnace in operation.
A drip leg (sediment trap) and a manual shut-off valve must be
provided immediately upstream of the gas control on the heating
unit. To facilitate servicing of unit, installation of a union is recom-
mended. See Fig. 149.
Pressure Testing
Connect a fitting and pressure gage suitable for measuring gas
pressure to 1/8 in. NPT tap provided on the manual shut-off valve
NOTE:
See
the
section,
Vented Duct Furnaces," on page 190 for
vent pipe diameters.
Category III Horizontal Furnace Venting (through Sidewall)
(Only dedicated furnace venting permitted. Each furnace must have its own individual vent pipe and terminal.)
PRESSURE
REGULATOR
GAS
SUPPLY
"Vertically
AIR-HANDLING UNIT
Fig. 147 — Indoor Horizontal Venting
MAX. 13.5 in. wg
Fig. 148 — Inlet Pressure for Multiple Heaters
tapping (see Fig. 149) or the inlet side of the gas valve (Fig. 150-
152). For multiple heater installations, measure inlet pressure to
each heater serviced by a single regulator with all heaters in opera-
tion. See Fig. 148.
IMPORTANT: When pressure testing at 1/2 psig or less, close
the manual shut-off valve on the appliance before testing. When
pressure testing the gas supply line at 1/2 psig or greater, close
the manual shut-off valve and disconnect the heater from supply
line to be tested. Cap or plug the supply line.
All field gas piping must be pressure and leak-tested prior
to operation. Never use an open flame to check for leaks as
combustion and personal injury may result. Use a soap
solution or other leak detecting solution.
5 FT. (1.52 M) MIN.
50 FT. (15.35 M) MAX. EQUIV. LENGTH
1/4 IN. (6 mm) PITCH PER
1 FT. (305 mm) HORIZONTAL
RUN
SEE VENT PIPE
DIAMETER TABLE
FOR
VENT DIAMETER
FIELD FABRICATED
VENT TO EACH
EXHAUST CONNECTION
CONDENSATE
DRAIN
UNIT 1
UNIT 2
192
WARNING
1 FT.
MIN.
LISTED VENT
TERMINAL
3 FT. MIN. (0.91 m) ABOVE
CONDENSATE
HIGHEST SNOWFALL
DRAIN
EXTERIOR WALL
MINIMUM INLET PRESSURE
REQUIRED AT LAST HEATER
UNIT 3
a39-4397
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