Allied Downflow or Horizontal 2 Stage Heat Variable Speed Gas Fired Non-Condensing Warm Air Furnace Installation And Servicing Instructions page 20

The gas control (Figure 13) has two separate
pressure regulator adjustment screws, one for 1
(marked "LO") and the second one for 2
"HI"). The adjusting screws are positioned on either
side of the barbed fitting.
adjustment is sensitive: one turn of the adjusting
screw will result in a relatively large change in
manifold pressure. Turn regulator-adjusting screws
IN (clockwise) to
(counterclockwise) to decrease presure.
Set the unit on high fire and adjust the 2
fire pressure regulator to the required setting. Disconnect
the violet wire from the "HI" terminal on the gas control
and the burners will drop down to the 1
st
then adjust the 1 stage pressure regulator setting as
required. Gas input must never exceed the value shown
on the furnace rating label. These units are equipped for
rated input at manifold pressures of 2.3" w.c. (1
nd
and 3.5" w.c. (2 stage) for natural gas.
furnaces have been converted for use with LP (propane)
gas, the manifold pressures are 6.4" w.c. (1
nd
10.0" w.c. (2 stage).
reconnect violet wire and furnace should go up to 2
stage high fire. Turn OFF gas, replace manifold pressure
tap pipe plug, regulator adjustment vent cap, and turn ON
gas.
At higher altitudes and varying heating valves,
manifold pressure or orifice changes maybe
required. Consult Tables 7 and 8 for appropriate
values. Failure to follow this warning could lead to
a hazardous furnace operating condition and result
in serious bodily injury or loss of life.
Determining Furnace Input - Natural Gas Only
NOTE: All access doors must be in place when checking
gas input.
1. Turn OFF all other gas appliances (except for pilot
burners) served by the same gas meter.
2. With furnace operating in full heat cycle, note how
many seconds it takes for one full revolution of the
smallest dial on the meter. Typically, this will be a
1/2 - or - 1 - cubic foot test dial.
3. Using the number of seconds for one revolution and
the size of the meter dial, determine the cubic foot
per hour of gas flow by using the formula provided
below or Table 5.
Number of Dial Revolutions x Cubic Foot/Revolution x 3600
Cubic Ft/Hr =
Time (in seconds) Required for Number of Timed Revolutions
20571201
st
nd
stage (marked
The pressure regulator
increase pressure,
nd
stage high
st
stage low fire,
st
When these
st
stage) and
After proper adjustments,
TABLE 5
stage
Seconds for
One
Revolution
10
12
14
OUT
16
18
20
22
24
26
28
30
32
34
stage)
4. Calculate the furnace input using the following
formula:
nd
The local gas supplier should be able to provide the
heating value of the gas, in BTU/cubic foot.
specific value is not available, use 1000 BTU/cubic
foot for Natural gas or 2500 BTU/cubic foot for
Propane (LP).
Furnace input should be maintained within ± 2% of
the value on the rating plate or appropriate altitude
derate.
orifices size if required.
5. Calculate the unit's actual input rate.
Example:
Input = 1015 Btu/cu. ft. X 1 rev X 2 cu. ft./rev. X 3600
Input = 121,800 Btu/hr.
Issue 0527
Gas Rate (Cubic Feet per Hour)
TEST DIAL
1/2 1 2 Seconds for
Cubic Cubic Cubic One
Feet Foot Feet Revolution
160 360 720 36
150 300 600 38
129 257 514 40
113 225 450 42
100 200 400 44
90 180 360 46
82 164 325 48
75 150 300 50
69 138 276 52
64 129 258 54
60 120 240 56
56 113 226 58
53 106 212 60
BTUH = Cubic Ft/Hr x BTU/Cubic Foot
Adjust manifold pressure or change
If the heating value of the natural gas is 1015
Btu/cu. and it takes 60 seconds to burn 2 cu.
ft. of gas then:
60 sec.
TEST DIAL
1/2 1 2
Cubic Cubic Cubic
Feet Foot Feet
50 100 200
47 95 190
45 90 180
43 86 172
41 82 164
39 78 156
37 75 150
36 72 144
35 69 138
34 67 134
32 64 128
31 62 124
30 60 120
If a
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