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The inner-cone combustion process will occur in increased levels, and will release more of the
harmful by-products, CO and Aldehydes. The level of secondary air will no longer be enough to
convert these chemicals into the safe by-products CO
2
and H
2
O, and there will be higher levels of
dangerous chemicals released into the room.
NOTE: It is normal for the burners without mixing tubes to have blowing flames during the first
minute of operation. When the burner is cold, primary air injection is increased. Once the burner
heats, the injection of primary air is reduced and the flames settle.
Not Enough Primary Air
The reduction of primary air slows the burning process and results in the inner cone rising higher
in the flame. Less burning takes place in the inner cone. A larger amount of the by-products that
would be consumed in the inner cone pass into the outer cone.
The size of the outer cone is also reduced by the lack of primary air. The outer cone cannot consume
the volume of by-products flowing from the inner cone. A percentage of these by-products flow into
the outer envelope where the carbon content of the by-product is burned, causing the flame to have
yellow tips (see Figure 3-16).
Figure 3-16
Outer Envelope
Yellow Tipping In
Outer Envelope
Outer Cone
Inner Cone
Unburned
Air/Gas
Over-Fueled Burner
Over-fueling of the burner can be caused by one of three common causes:
• Excessive gas pressure entering the burner
• The BTU rating of the gas can be too high for the burner
• An oversized gas metering orifice
It is difficult to recognize the difference between an over-fueled burner and too much primary air.
In both cases, the burner flame length extends too far off of the burner (see Figure 3-17).
Figure 3-17
Outer Envelope
Yellow Tipping
And Soot Can Appear
In Extreme Cases
Outer Cone
Flame Lifts
Off Burner
Flame
Too Tall