6. GasSupplyand Piping
Poison carbon monoxide gas, fire and explosion
hazard.
Models designated for Natural Gas areto be used
with Natural Gas ONLY, unless properly con-
verted to use with LP gas.
Failure to follow these instructions can result in
death, personal injury and/or property damage.
Gas SupplyRequirements
• Use only the Type of gas approved for this furnace. See rat-
ing plate for approved gas type.
• Gas input must not exceed the rated input shown on the rat-
ing plate. Overfiring will result in failure of heat exchanger
and cause dangerous operation.
• Do not allow minimum supply pressure to vary downward.
Doing so will decrease input to furnace. Refer to Table 2 for
Gas supply and manifold pressures.
Gas Pressures
Gas
Type
Natural
Propane
Supply Pressure
Recommended Max.
7" 14"
(1.7 kPa) (3.5 kPa)
11" 14"
(2.7 kPa) (3.5 kPa)
Min.
4.5"
(1.1 kPa)
1t"
(2.7 kPa)
Manifold
Pressure
3.5 _
(0.9 kPa)
10"
(2.5 kPa)
Table 3 Orifice Sizes (below 2000')for
Downflow
Heating Value
Gas Manifold Specific (BTU per
Type Pressure Gravity Cubic Ft.)
Natural 800
3.5" w.c. 900
0.9kPa 0.6
1000
W.C.
1100
10" W.C.
Propane 2.5kPa 1.53 2500
w.c.
Orifice Size
(Drill #)
40
41
42
43
54
Natural Gas InputRatingCheck
The gas meter can be used to measure input to furnace. Rating is
based on a natural gas BTU content of 1,000 BTU's per cubic foot.
Check with gas supplier for actual BTU content.
1. Turn OFF gas supply to all appliances other than furnace and
start furnace.
2. Time how many seconds it takes the smallest dial on the gas
meter to make one complete revolution. Refer to Example.
Note: If meter uses a 2 cubic foot dial, divide results (se-
conds) by two.
Example
Natural Gas No. of Seconds Time Per Cubic BTU Per
BTU Content Per Hour Foot in Seconds Hour
1,000 3,600 48 75,000
1,000 x 3,600 + 48 = 75,000 BTUH
3. Relight all appliances and ensure all pilots are operating.
Orifice Sizing
NOTE: Factory sized orifices for natural and LP gas are listed in
the furnace Technical Support manual.
For downflow ensure furnace is equipped with the correct main
burner orifices. Refer to Table 3 for correct orifice size for a given
heating value and specific gravity for natural and propane gas.
Note that this chart is ONLY for downflow installations below
2000' in altitude.
Operation Above 2000' Altitude
Fire, Explosion, Poison carbon monoxide gas haz-
ard.
This conversion shall be done by a qualified ser-
vice agency in accordance with the Manufactur-
er's instructions and all applicable codes and re-
quirements, or in the absence of local codes, the
applicable national codes.
Failure to follow these instructions exactly can re-
sult in death, personal injury and/or property dam-
age.
These units may be used at full input rating when installed at alti-
tudes up to 2000'. When installed above 2000', the input must be
decreased 2% (natural) or 4% (LP) for each 1000' above sea level.
This may be accomplished by a simple adjustment of manifold
pressure or an orifice change, or a combination of a pressure ad-
justment and an orifice change. The changes required depend on
the installation altitude and the heating value of the fuel. Table 4 &
Table 5 show the proper furnace manifold pressure and gas ori-
fice size to achieve proper performance based on elevation
above sea level for both natural gas and propane.
To use the natural gas table, first consult your local gas utility for
the heating value of the gas supply. Select the heating value on
the vertical border and follow across the table until the appropriate
elevation for the installation is reached. The first value in the box
at the intersection of the heating value and elevation will be the
manifold pressure required. If a gas orifice change is also re-
quired, the box is shaded. The required orifice size is shown atthe
bottom of the table.
Sea Level
High Altitude Input Rate = Nameplate x (Multiplier)
Input Rate
Elevation
2000'-2999'
3000'-3999'
4000'-4999'
5000'-5999'
6000'-6999'
7000'-7999'
High Altitude Multiplier
Natural LP Gas
0.96 0.92
0.94 0.88
0.92 0.84
0.90 0.80
0.88 0.76
0.86 0.72
A High Altitude Kit is available for downflow which includes re-
strictors, orifices and installation instructions.
Natural Gas - 1160993
LP Gas - 1160992
_] 44t 012308 01
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