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6.
Shut unit off and remove manometer as soon as an
accurate reading has been obtained. Turn the supply
and manifold 3/32" hex screw one revolution back into
the gas valve.
7.
Start unit and check for gas leaks. Seal if any found.
Proper Combustion
Furnace should operate a minimum 15 minutes with correct
manifold pressure and gas flow rate before checking
combustion. Table 14 shows acceptable combustion for
all NF80DT models. The maximum carbon monoxide
reading should not exceed 100 ppm.
Capacity
CO
High Fire
Low Fire
Table 14.
Capacity
Gas
Natrual
070
LP/Propane
3
Natrual
090
LP/Propane
3
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.
Capacity
0 - 4,500 ft.
All
No Change
NOTE: A natural to LP/Propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the
conversion procedure.
Page 32 of 38
% for Nat
CO
% for LP
2
2
6.8 - 7.4
7.5 - 9.0
4.2 - 5.7
5.0 - 6.0
Manifold Pressure
in. wg. 0 - 4,500 ft.
Low Fire
High Fire
1.7
3.5
4.5
10.0
1.7
3.5
4.5
10.0
Table 15. Manifold Pressure and Line Pressure at Various Altitudes
High Altitude Pressure Switch Kit
4,501 - 7,500 ft.
91W53
Table 16. Orifice Kits and Pressure Switch Kits at Various Altitudes
High Altitude
The manifold pressure may require adjustment and
combustion air pressure switch may need replacing to
ensure proper combustion at higher altitudes. Refer to
Table 15 for manifold pressure and Table 16 for pressure
switch change and gas conversion kits.
For safety, shut unit off and remove manometer as soon
as an accurate reading has been obtained. Take care to
replace pressure tap plug.
Manifold Pressure
in. wg. 4,501 - 7,500 ft.
in. wg. 7,501 - 10,000 ft.
Low Fire
High Fire
1.5
3.2
4.5
10.0
1.5
3.0
4.5
10.0
High Altitude
Natural Gas Oririce
7,501 - 10,000 ft.
7,501 - 10,000 ft.
73W35
Issue 2220
IMPORTANT
Manifold Pressure
2
Low Fire
High Fire
1.7
3.5
4.5
10.0
1.7
3.5
4.5
10.0
Natural to LP/Propane Kit
Kit
0 - 7,500 ft.
51W01
11K48
Supply Line Pressure
in. wg.
Min.
Max.
4.5
13.0
11.0
13.0
4.5
13.0
11.0
13.0
7,501 - 10,000 ft.
11K47
508145-01G / 31-5000660
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