18
When the gas piping enters through the top of the fur-
nace (Figure 18), the installer must supply the following
fittings (starting from the gas valve):
90 degree elbow
1-1/2 inch close nipple
90 degree elbow
Straight pipe to reach exterior of furnace
Figure 18
Gas Inlet Through Furnace Top Side
(GUD)
A ground joint union, drip leg, and manual shutoff valve
must also be supplied by the installer. In some cases,
the installer may also need to supply a transition piece
from 1/2 inch to another pipe size.
Checking Gas Piping
CAUTION
To prevent personal injury or property
damage due to fire, the following instruc-
tions must be performed regarding gas
connections, pressure testing, location
of shutoff valve and installation of gas
piping.
Before placing in operation, leak test the unit and
gas connections. To avoid the possibility of ex-
plosion or fire, never use a match or open flame
to test for leaks. Never exceed specified pres-
sures for testing. Higher pressure may damage
the gas valve and cause overfiring, resulting in
heat exchanger failure.
This unit and shutoff valve must be disconnected
from the gas supply piping system before supply
piping system pressure testing with test pressures
in excess of 1/2 psig (3.48 kPa).
This unit must be isolated from the gas supply
system by closing its manual shutoff valve before
pressure testing of gas supply piping system with
test pressures equal to or less than 1/2 psig (3.48
kPa).
Tanks and Piping - Propane Gas Units
WARNING
To prevent death, personal injury or prop-
erty damage due to fire or explosion
caused by a propane gas leak, install a
gas detecting warning device. Since rust
can reduce the level of odorant in pro-
pane gas, a gas detecting warning de-
vice is the only reliable way to detect a
propane gas leak. Contact a local pro-
pane gas supplier about installing a gas
detecting warning device.
All propane gas equipment must conform to the safety
standards of the National Board of Fire Underwriters
(See NBFU Manual 58).
For satisfactory operation, propane gas pressure must
be 10 inch W.C. at the furnace manifold with all gas
appliances in operation. Maintaining proper gas pres-
sure depends on three main factors:
1. Vaporization rate, depending on temperature of the
liquid, and wetted surface area of the container or
containers.
2. Proper pressure regulation. Two-stage regulation is
recommended for both cost and efficiency.
3. Pressure drop in lines between regulators, and be-
tween second stage regulator and the appliance.
Pipe size will depend on length of pipe run and total
load of all appliances.
Complete information regarding tank sizing for vaporiza-
tion, recommended regulator settings, and pipe sizing
is available from most regulator manufacturers and
propane gas suppliers.
Since propane gas will quickly dissolve white lead or
most standard commercial compounds, special pipe
dope must be used. Shellac base compounds resistant
to the actions of liquefied petroleum gases such as
Gasolac, Stalactic, Clydes or John Crane are satisfac-
tory.
Refer to Figure 19 for typical propane gas installations.
