46
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 opera-
tion.
IMPORTANT:
ENSURE that the furnace gas valve is not
to 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 test-
ing that exceeds 1/2 PSIG. (3.48 kPa).
Natural gas supply pressure must be 5" to 10.5" w.c.
LP gas supply pressure must 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 sup-
ply pressure is 11" w.c. for LP gas.
GAS SUPPLY
GAS PRESSURE
TABLE 11
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 de-
termined by consulting the local natural gas utility or the LP gas supplier.
!
CAUTION
ELEVATIONS ABOVE 2000 FT. REQUIRE THAT THE
FURNACE INPUT RATING BE ADJUSTED AND THAT
THE SIZE OF THE BURNER ORIFICES BE RECAL-
CULATED BASED ON ELEVATION AND GAS HEAT-
ING VALUE. THE BURNER ORIFICES MAY (OR MAY
NOT) NEED TO BE CHANGED. SEE THE SECTION
TITLED “HIGH ALTITUDE INSTALLATIONS” OF THIS
BOOK FOR INSTRUCTIONS.
Ga
s S
up
pl
y
FIGURE 31
OUTLET / MANIFOLD TAP
ST-A1194-88-00
ST-A1194-88-00
ST-A1194-89-00
SUPPLY PRESSURE TAP
OFF/ON SWITCH
LP JUMPER WELL
(INSERT JUMPER HERE)
ADJUSTMENT WELL
ST-A1194-89-00
FIGURE 32
