38
NEVER PURGE A GAS LINE INTO
THE COMBUSTION CHAMBER.
NEVER USE MATCHES, FLAME OR
ANY IGNITION SOURCE FOR
CHECKING LEAKAGE. FAILURE TO
ADHERE TO THIS WARNING CAN
CAUSE A FIRE OR EXPLOSION
RESULTING IN PROPERTY
DAMAGE, PERSONAL INJURY OR
DEATH.
To check for gas leakage, use an
approved chloride-free soap and water
solution, or other approved method.
FIGURE 36
TYPICAL GAS VALVE
GAS VALVE #60-101921-02
use a pipe compound resistant to the
action of liquefied petroleum gases on
all threaded connections.
IMPORTANT: When making gas pipe
connections, use a back-up wrench to
prevent any twisting of the main gas
valve and manifold. Do not
overtighten gas valve on pipe.
Any strains on the gas valve can
change the position of the gas orifices
in the burners. This can cause erratic
furnace operation.
IMPORTANT: Do not run a flexible
gas connector inside the furnace. The
gas pipe gasket in the cabinet does
not seal around a flexible gas line.
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 serviced another gas
appliance. Massachusetts law
requires that all flexible connectors be
less than 36”.
It is important to have all openings
in the cabinet burner compartment
sealed for proper furnace
operation.
IMPORTANT: ENSURE that the
furnace gas valve not be subjected to
high gas line supply pressures.
DISCONNECT the furnace and its
individual manual gas stop from the
gas supply piping during any
pressure testing that exceeds 1/2
PSIG. (3.48 kPa).
GAS PRESSURE
Natural gas supply pressure should
be 5" to 10.5" w.c. LP gas supply
pressure should be 11" to 13" w.c.
This pressure must be maintained
with all other gas-fired appliances
in operation.
The minimum gas supply pressure to
the gas valve for proper furnace input
adjustments is 5" w.c. for natural gas,
however 6" to 7" is recommended.
The minimum gas supply pressure is
11" w.c. for LP gas.
ELEVATIONS ABOVE 2000 FT
REQUIRE THAT THE FURNACE
INPUT RATING BE ADJUSTED AND
THAT THE SIZE OF THE BURNER
ORIFICES BE RE-CALCULATED
BASED ON ELEVATION AND GAS
HEATING VALUE. THE BURNER
ORIFICES MAY (OR MAY NOT)
NEED TO BE CHANGED. SEE THE
SECTION TITLED “HIGH ALTITUDE
INSTALLATIONS” OF THIS BOOK
FOR INSTRUCTIONS.
!
WARNING
TABLE 6
NATURAL GAS PIPE CAPACITY TABLE (CU. FT./HR.)
Capacity of gas pipe of different diameters and lengths in cu. ft. per hr. with pressure drop of 0.3 in. and specific
gravity of 0.60 (natural gas).
Nominal Length of Pipe, Feet
Iron Pipe
Size, Inches 10 20 30 40 50 60 70 80
1/2 132 92 73 63 56 50 46 43
3/4 278 190 152 130 115 105 96 90
1 520 350 285 245 215 195 180 170
1-1/4 1,050 730 590 500 440 400 370 350
1-1/2 1,600 1,100 890 760 670 610 560 530
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour
required for the gas input rating of the furnace. By formula:
Gas Input of Furnace (BTU/HR)
Cu. Ft. Per Hr. Required =
Heating Value of Gas (BTU/FT
3
)
The gas input of the furnace is marked on the furnace rating plate. The heating value of the gas (BTU/FT
3
) may be
determined by consulting the local natural gas utility or the LP gas supplier.
GAS VALVE
This furnace has a 24-volt gas valve.
It has ports for measuring supply and
manifold gas pressure. The valve
body contains a pressure regulator to
maintain proper manifold gas
pressure.
A control switch is on the valve body.
It can be set to only the “ON” or
“OFF” positions. The gas valve is a
slow-opening valve. See Figure 36.
When energized, it takes 6 to 8
seconds to fully open.
CAUTION
!
GAS CONTROL
SWITCH
INLET
PRESSURE
TAP
OUTLET
PRESSURE
TAP
LOW FIRE
MANIFOLD
PRESSURE
ADJUSTMENT
HIGH FIRE
MANIFOLD
PRESSURE
ADJUSTMENT
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