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IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
G− Proper Combustion
Furnace should operate minimum 15 minutes with correct
manifold pressure and gas flow rate before checking com-
bustion. See sections E− and F−. Take combustion sample
beyond the flue outlet. Table 9 shows acceptable combus-
tion for ALL EL280UH models. The maximum carbon
monoxide reading should not exceed 50 ppm.
Unit
Gas
Input
Low Fire
Natural
070
3
LP/propane
Natural
090
3
LP/propane
Natural
110
LP/propane
3
Natural
135
3
LP/propane
1
This is the only permissible derate for these units.
2
Natural gas high altitude orifice kit required.
3
A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion
procedure.
NOTE − Units may be installed at altitudes up to 4500 ft. above sea level without modifications.
High Altitude Pressure Switch Kit
Unit
Input
0 − 4500 ft.
4501 − 7500 ft.
070
91W53
090
91W53
No Change
110
91W53
135
73W33
NOTE − A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion
procedure.
Manifold Pressure Settings at all Altitudes
Manifold
Pressure in.wg.
0−4500 ft.
High Fire
Low Fire
1.7
3.5
4.9
10.0
1.7
3.5
4.9
10.0
1.7
3.5
4.9
10.0
1.7
3.5
4.9
10.0
Pressure Switch and Gas Conversion Kits at all Altitudes
7501 − 10,000 ft.
73W35
73W35
73W35
73W34
Firing Rate
High Fire
Low Fire
H− High Altitude
The manifold pressure may require adjustment and com-
bustion air pressure switch may need replacing to ensure
proper combustion at higher altitudes. Refer to table 10 for
manifold pressure and table 11 for pressure switch change
and gas conversion kits.
TABLE 10
Manifold
Pressure in.wg.
1
4501−7500 ft.
High Fire
Low Fire
1.5
3.2
4.9
10.0
1.5
3.2
4.9
10.0
1.5
3.2
4.9
10.0
1.5
2.8
4.9
10.0
TABLE 11
High Altitude
Natural Gas Kit
7501 − 10,000 ft.
0 − 7500 ft
73W37
77W07
Page 21
TABLE 9
CO
%
CO
2
For Nat
6.0 − 7.5
7.0 − 8.5
5.0 − 6.5
5.8 − 7.3
Manifold
Supply Line
Pressure in.wg.
Pressure
2
7501 − 10,000 ft.
High Fire
Min
1.7
3.5
4.5
4.9
10.0
11.0
1.7
3.5
4.5
4.9
10.0
11.0
1.7
3.5
4.5
4.9
10.0
11.0
1.7
3.5
4.5
4.9
10.0
11.0
LP/Propane Gas Kit
7501 − 10,000 ft.
77W11
%
2
For L.P.
in. w.g.
Max
13.0
13.0
13.0
13.0
13.0
13.0
13.0
13.0
LP/Propane to
Natural Kit
0 − 7500 ft.Min
77W09
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