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ADJUSTING OR CHECKING
FURNACE INPUT
CAUTION
!
ELEVATIONS ABOVE 2000 FT
REQUIRE THAT THE FURNACE
INPUT RATE 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.
NATURAL GAS:
The maximum gas supply pressure to
the furnace should be 10.5" W.C. for
natural gas. The minimum gas supply
pressure for purposes of input
adjustment to the furnace should be 5"
W.C.
A properly calibrated manometer or
gauge is required for accurate gas
pressure readings.
The manifold pressure should be set at
3.5" W.C. for natural gas. Only small
variations in the gas flow should be
made by means of the pressure
regulator adjustment.
To adjust the pressure regulator:
1. Remove the regulator cap.
2. Turn the adjustment screw clockwise
to increase pressure or
counterclockwise to decrease
pressure.
3. Replace the regulator cap securely.
20
LP GAS:
Furnaces for use on LP gas, the LP gas
supply pressure must be set between
11.0" and 13.0" W.C. by means of the
tank or branch supply regulators. The
furnace manifold pressure should be set
at 10" W.C. at the gas control valve. For
elevations up to 8,000 feet, rating plate
input ratings apply. For high altitudes
(elevations 8,000 and over) and for any
necessary major changes in the gas
flow rate the orifice spud must be
changed.
TO CHANGE ORIFICE SPUDS:
1. Shut off the manual main gas valve
and remove the gas manifold.
2. Replace the orifice spuds.
3. Reassemble in reverse order.
4. Turn the gas supply back on and
check for leaks.
5. Check for proper operation and
manifold pressure.
TABLE 4
METER TIME IN MINUTES AND SECONDS FOR NORMAL
INPUT RATING OF FURNACES EQUIPPED FOR NATURAL OR LP GAS
METER
INPUT
SIZE
BTU/HR
CU. FT.
ONE
50,000
TEN
ONE
75,000
TEN
ONE
100,000
TEN
ONE
125,000
TEN
ONE
150,000
TEN
Heating Value of Gas (BTU/Ft
Input BTU/HR =
Time in Seconds (for 1 cu.ft.) of Gas
Check of input is important to prevent
over firing of the furnace beyond its
design-rated input. NEVER SET INPUT
ABOVE THAT SHOWN ON THE
RATING PLATE.
TO CHECK FURNACE INPUT:
1. Make certain that all other gas
appliances are shut off, with the
exception of pilot burners.
2. Start the furnace
3. Time the meter to measure the time
required to burn one cubic foot of
gas.
4. Use Table 4 to determine input rate.
HEATING VALUE OF GAS BTU PER CU. FT.
900
1000
1040
MIN. SEC. MIN. SEC. MIN. SEC. MIN. SEC. MIN. SEC.
1
5
1
12
1
15
10
50
12
00
12
30
0
44
0
48
0
50
7
12
8
0
8
19
0
33
0
36
0
38
5
24
6
0
6
15
0
26
0
29
0
30
4
19
4
48
5
0
0
31
0
24
0
25
3
36
4
0
4
10
3
) x 3600 x correction factor
1100
2500
1
18
3
20
13
12
30
00
0
53
2
0
8
48
20
0
0
40
1
30
6
36
15
0
0
32
1
12
5
17
12
0
0
26
1
0
4
20
10
0
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