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GAS PRESSURE
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 con-
nector, always use a new listed connector. Do not use a
connector which has previously serviced another gas ap-
pliance. Massachusetts law requires that all flexible con-
nectors 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.
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 SEC-
TION TITLED "HIGH ALTITUDE INSTALLATIONS"
OF THIS BOOK FOR INSTRUCTIONS.
GAS VALVE
This furnace has a 24-volt gas valve. It has ports for meas-
uring supply and manifold gas pressure. The valve body
TABLE 12
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
Iron Pipe
Size, Inches
10
20
1/2
132
92
3/4
278
190
1
520
350
1-1/4
1,050
730
1-1/2
1,600
1,100
After the length of pipe has been determined, select the pipe size which will provide the minimum cubic feet per hour re-
quired for the gas input rating of the furnace. By formula:
Cu. Ft. Per Hr. Required
The gas input of the furnace is marked on the furnace rating plate. The heating value of the gas (BTU/FT
by consulting the local natural gas utility or the LP gas supplier.
FIGURE 37
TYPICAL GAS VALVE (WHITE RODGERS)
INLET
PRESSURE TAP
NEVER PURGE A GAS LINE INTO THE COMBUS-
TION CHAMBER. NEVER USE MATCHES, FLAME
OR ANY IGNITION SOURCE FOR CHECKING LEAK-
AGE. 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 AP-
PROVED CHLORIDE-FREE SOAP AND WATER SO-
LUTION, OR OTHER APPROVED METHOD.
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 37.
When energized, it takes 2 to 3 seconds to fully open.
Length of Pipe, Feet
30
40
50
60
73
63
56
50
152
130
115
105
285
245
215
195
590
500
440
400
890
760
670
610
Gas Input of Furnace (BTU/HR)
=
Heating Value of Gas (BTU/FT
GAS SUPPLY
OUTLET PRESSURE TAP
70
80
46
43
96
90
180
170
370
350
560
530
3
)
3
) may be determined
HIGH-FIRE
MANIFOLD
PRESSURE
ADJUSTMENT
LOW-FIRE
MANIFOLD
PRESSURE
ADJUSTMENT
73
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