185
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 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 operation. See Fig. 148.
IMPORTANT: Gas pressure to appliance controls must never
exceed 13.5 in. wg (
1
/
2
psig).
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.
WARNING
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.
1 FT.
MIN.
EXTERIOR WALL
3 FT. MIN. (0.91 m) ABOVE
HIGHEST SNOWFALL
1/4 IN. (6 mm) PITCH PER
1 FT. (305 mm) HORIZONTAL
RUN
5 FT. (1.52 M) MIN.
50 FT. (15.35 M) MAX. EQUIV. LENGTH
CONDENSATE
DRAIN
SEE VENT PIPE
DIAMETER TABLE
FOR
VENT DIAMETER
LISTED VENT
TERMINAL
CONDENSATE
DRAIN
AIR-HANDLING UNIT
FIELD FABRICATED
VENT TO EACH
EXHAUST CONNECTION
Fig. 147 —
Indoor Horizontal Venting
a39-4397
Category III Horizontal Furnace Venting (through Sidewall)
(Only dedicated furnace venting permitted. Each furnace must have its own individual vent pipe and terminal.)
NOTE: See the section, “Vertically
Vented Duct Furnaces,” on page
183 for
vent pipe diameters.
UNIT 1
UNIT 2
UNIT 3
MINIMUM INLET PRESSURE
REQUIRED AT LAST HEATER
MAX. 13.5 in. wg
PRESSURE
REGULATOR
GAS
SUPPLY
Fig. 148 —
Inlet Pressure for Multiple Heaters
