11
5-564
Air Shutter Adjustment
Proper operation provides a soft blue flame with a well-defined
inner core. A lack of primary air will reveal soft yellow-tipped
flames. Excess primary air produces short, well-defined flames
with a tendency to lift off the burner ports. For both natural
and propane gas, the air shutters can be adjusted to control
the burner flame height. The air shutters can be accessed by
reaching behind the gas valve in Figure
10.3. The larger models
may require the removal of the manifold (see Manifold Assembly
Removal).
Natural Gas Flame Control
Control of burner flames on duct furnaces utilizing natural gas
is achieved by resetting the primary air shutters (See Figure
19.1) to either increase or decrease primary combustion air.
Prior to flame adjustment, operate duct furnace for about fifteen
minutes. The main burner flame can be viewed after loosening
and pushing aside the gas designation disc on the side of the
burner box.
To increase primary air, loosen the air shutter set screws and
move the air shutters closer to the manifold until the yellow-
tipped flames disappear. (See Figure 19.1 for air shutter and
heat exchanger support locations.) To decrease primary air,
move the air shutters away from the manifolds until flames
no longer lift from burner ports, but being careful not to cause
yellow tipping. Retighten set screws after adjustment.
Propane Gas Flame Control
An optimum flame will show a slight yellow tip. Prior to flame
adjustment, operate furnace for at least fifteen minutes. Loosen
air shutter set screws and move the air shutters away from the
manifold to reduce the primary air until the yellow flame tips
appear. Then increase the primary air until yellow tips diminish
and a clean blue flame with a well defined inner cone appears.
Model Size Type of Gas Natural Propane
Btu/Cu. Ft. 1040 2500
Specific Gravity 0.60 1.53
High Fire Manifold Pressure No. of
Inches of Water Column 3.5 10 Orifices
Cfh 72.1 30.0
1
Orifice Drill Size 20 37
Cfh 96.1 40.0
2
Orifice Drill Size 30 45
Cfh 120.2 50.0
2
Orifice Drill Size 25 42
Cfh 144.2 60.0
3
Orifice Drill Size 30 45
Cfh 168.3 70.0
3
Orifice Drill Size 27 43
Cfh 192.3 80.0
3
Orifice Drill Size 23 40
Cfh 216.3 90.0
3
Orifice Drill Size 20 37
Cfh 240.4 100.0
4
Orifice Drill Size 25 42
Cfh 288.7 120.0
4
Orifice Drill Size 20 37
Cfh 336.5 140.0
6
Orifice Drill Size 27 43
Cfh 384.6 160.0
6
Orifice Drill Size 23 40
START-UP PROCEDURE
100
125
150
175
400
75
350
300
250
225
200
Table 11.1 - Manifold Pressure and Gas Consumption
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