Page 34
Gas Piping
Gas supply piping should not allow more than 0.5”W.C.
drop in pressure between gas meter and unit. Supply gas
pipe must not be smaller than unit gas connection.
CAUTION
If a flexible gas connector is required or allowed by
the authority that has jurisdiction, black iron pipe
shall be installed at the gas valve and extend outside
the furnace cabinet. The flexible connector can then
be added between the black iron pipe and the gas
supply line.
WARNING
Do not exceed 600 in-lbs (50 ft-lbs) torque when at
taching the gas piping to the gas valve.
1 - Gas piping may be routed into the unit through either
the left‐ or right‐hand side. Supply piping enters into
the gas valve from the side of the valve as shown in
figure 49.
2 - When connecting gas supply, factors such as length of
run, number of fittings and furnace rating must be con
sidered to avoid excessive pressure drop. Table 11
lists recommended pipe sizes for typical applications.
NOTE
- Use two wrenches when connecting gas pip
ing to avoid transferring torque to the manifold.
3 - Gas piping must not run in or through air ducts, clothes
chutes, chimneys or gas vents, dumb waiters or eleva
tor shafts. Center gas line through piping hole. Gas
line should not touch side of unit. See figures 49 and
50.
4 - Piping should be sloped 1/4 inch per 15 feet (6mm per
5.6m) upward toward the gas meter from the furnace.
The piping must be supported at proper intervals, ev
ery 8 to 10 feet (2.44 to 3.05m), using suitable hangers
or straps. Install a drip leg in vertical pipe runs to serve
as a trap for sediment or condensate.
5 - A 1/8” N.P.T. plugged tap or pressure post is located
on the gas valve to facilitate test gauge connection.
See figure 57.
6 - In some localities, codes may require installation of a
manual main shut‐off valve and union (furnished by in
staller) external to the unit. Union must be of the
ground joint type.
IMPORTANT
Compounds used on threaded joints of gas piping
must be resistant to the actions of liquified petro
leum gases.
Leak Check
After gas piping is completed, carefully check all piping
connections (factory- and field-installed) for gas leaks. Use
a leak detecting solution or other preferred means.
Never use an open flame to test for gas leaks. Check all
connections using a commercially available soap solution
made specifically for leak detection.
The furnace must be isolated from the gas supply system
by closing its individual manual shut‐off valve during any
pressure testing of the gas supply system at pressures
greater than or equal to 1/2 psig (3.48 kPa, 14 inches w.c.).
FIGURE 48
MANUAL MAIN SHUT-OFF
VALVE WILL NOT HOLD
NORMAL TEST PRESSURE
CAP
FURNACE
ISOLATE
GAS VALVE
1/8” N.P.T.
PLUGGED TAP
IMPORTANT
When testing pressure of gas lines, gas valve must
be disconnected and isolated. See figure 48. Gas
valves can be damaged if subjected to pressures
greater than 1/2 psig (3.48 kPa).
WARNING
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warnings exactly could
result in serious injury, death, or property damage.
Never use an open flame to test for gas leaks. Check
all connections using a commercially available soap
solution made specifically for leak detection. Some
soaps used for leak detection are corrosive to cer
tain metals. Carefully rinse piping thoroughly after
leak test has been completed.
