Manifold Pressure Adjustment:
Turn OFF the gas and electrical before preceding!
Remove the manifold pressure tap pipe plug from the gas valve
and install a pressure tap and connect it to a manometer. Turn on
the gas and electrical supplies, then measure the manifold pressure
with the furnace in operation.
Remove the cap to access the screw for input adjustment
(Figure 1.12 Pressure Regulator). Turn regulator-adjusting
screw IN to increase pressure, OUT to decrease pressure. The
input rate must be maintained within +_2% of the value on the
rating plate.
For Natural gas, best results are obtained with a manifold
pressure of 3.2" to 3.5" water column. For units that have been
convened to LP (Propane) gases, a manifold pressure of 10" water
column is necessary. After proper adjustment, turn OFF gas,
replace pipe plug and tum ON gas.
Burner Orificing:
The furnace is supplied with standard orifices for the gas
shown on the rating plate. Table 1.13 shows combinations of
heating values and specific gravities for various gases, from which
proper input can be obtained.
I. Remove the manifold from the furnace, following the
insWuctions found on page 15.
2. Orifices may now be removed/replaced.
Table 1.13 BURNER ORIFICE SELECTION
Type of Gas @ Manifold Press. Orifice
(Heating Value - Specific Gravity) Size
Btu per Cu. Ft. (Drill #)
Natural Manifold Press.- 3.5"w.c.
800 - 0.6 40
900 - 0.6 41
1000 - 0.6 42
1100 - 0.6 43
Propane MnnifoldPress.- 10"w.c.
2500 - 1.53 54
After securing the manifold assembly, replace all other
components and/or wiring, being sure that all connections and
screws are tightened properly.
Altitude Derating _'U.S.ONLY):
The following information is provided as guidelines for
altitude derating and is not meant to supersede any state or local
codes. Local codes would have priority over any others and in
some case might limit your options in dealing with an altitude
derate situation.
The second guideline is to check with your local gas company
to find out if the gas supply in your area is derated. Gas deration
negates the necessity of performing any adjustment on the furnace.
If your gas supply is not derated, and regardless of the type of
gas used, installation of this furnace at an elevation above 2,000 ft.
requires an input reduction at the rate of four percent (4%) for each
1,000 ft. above sea level.
Unless an orifice change is specified by an applicable code, or
the furnace is to be installed above 6,000 feet the recommended
method of altitude derating this furnace is to appropriately lower
your manifold pressure. The appropriate manifold pressures based
on the elevation and the heating value can be found in Table 2.13.
Table 2.13 HIGH ALTITUDE MANIFOLD
PRESSURE DERATE
Altitude
(Fe_:t)
o
lOO0
2000
3000
40o0
50o0
6000
* Heating-Value based on
60F temperature.
*Heating Value of Natural Gas
(BTU/Fr3)
900 950
4.32 3.88
4.32 3.88
3.67 3.29
3.38 3.04
3.11 2.79
2.88 2.58
2.64 2.37
atmospheric pressure of 30 iabg and
L.P.
Propane
1000 1050 1100 2500
3.50 3.16 2.84 10
3.50 3.16 2.84 10
2.97 2.68 2.41 8.46
2.74 2.47 2.22 7.74
2.52 2.27 2.04 7.05
2.33 2.10 1.89 6.4
2.14 1.93 1.73 5.77
If local codes require an orifices change or if the furnace
installation is above 6,000 feet, field drilling of "blank" orifices
will be required (Ref Ducane P/N 2006608 for "blank" orifices).
The appropriate orifice size based on the elevation and the heating
value can be found in Table 3.13. Sizing of the orifice must be
based on the previously mentioned 4% derate for each 1,000 feet
for installations at/or above 2,000 feet rule and the orifices must be
chilled in such a way as to assure concentricity. Hand drilling of
orifices is totally unacceptable.
Table 3.13
Altitude
(Feet)
HIGH ALTITUDE ORIFICE SIZE DERATE
2000
30O0
4000
5000
6000
7000
8000
9000
10003
* Heating-Value based on
60F temperature.
*Heating Value of Natural Gas
03TU/Fr3)
900 950 1000 1050 1100
N.C. N.C. 43 43 44
N.C. N.C. 43 44 44
43 43 44 44 45
43 44 44 45
44 44 45 46
44 45 46 47
45 46 47 48
46 47 48 48
47 48 49 49
atmospheric pressure
LP.
Propane
2500
N.C.
N.C.
55
46 55
47 55
48 56
48 56
49 56
50 57
of 30 inhg and
20246506 Issue 9939 Page 13 of 22
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