Page 21
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.
TABLE 9
Firing Rate
CO
2
%
For
Nat
CO
2
%
For
L.P.
High Fire 6.0 − 7.5 7.0 − 8.5
Low Fire 5.0 − 6.5 5.8 − 7.3
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 Settings at all Altitudes
Unit
Input
Gas
Manifold
Pressure in.wg.
0−4500 ft.
Manifold
Pressure in.wg.
4501−7500 ft.
1
Manifold
Pressure in.wg.
7501 − 10,000 ft.
2
Supply Line
Pressure
in. w.g.
Low Fire High Fire Low Fire High Fire Low Fire High Fire Min Max
070
Natural 1.7 3.5 1.5 3.2 1.7 3.5 4.5 13.0
LP/propane
3
4.9 10.0 4.9 10.0 4.9 10.0 11.0 13.0
090
Natural 1.7 3.5 1.5 3.2 1.7 3.5 4.5 13.0
LP/propane
3
4.9 10.0 4.9 10.0 4.9 10.0 11.0 13.0
110
Natural 1.7 3.5 1.5 3.2 1.7 3.5 4.5 13.0
LP/propane
3
4.9 10.0 4.9 10.0 4.9 10.0 11.0 13.0
135
Natural 1.7 3.5 1.5 2.8 1.7 3.5 4.5 13.0
LP/propane
3
4.9 10.0 4.9 10.0 4.9 10.0 11.0 13.0
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.
TABLE 11
Pressure Switch and Gas Conversion Kits at all Altitudes
Unit
Input
High Altitude Pressure Switch Kit
High Altitude
Natural Gas Kit
LP/Propane Gas Kit
LP/Propane to
Natural Kit
0 − 4500 ft. 4501 − 7500 ft. 7501 − 10,000 ft. 7501 − 10,000 ft. 0 − 7500 ft 7501 − 10,000 ft. 0 − 7500 ft.Min
070
No Change
91W53 73W35
73W37 77W07 77W11 77W09
090 91W53 73W35
110 91W53 73W35
135 73W33 73W34
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.
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