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To secure safe and efficient operation of gas or fuel oil burners it is common to test the burners for

• carbon dioxide
• smoke
• excess air (O₂/CO₂)
• stack temperature
• draft
• NO_x

Carbon Dioxide - CO₂

When the CO₂ content of the flue gas is low (less than 8 percent) heat is lost up the chimney and the operation is inefficient.

Low carbon dioxide content may be caused by

• to small burner nozzle
• air leakage into the furnace or boiler
• underfiring in the combustion chamber

When the CO₂ content of the flue gas is too high it is common with excess smoke in the flue gas. High carbon dioxide content may be caused by

• insufficient draft
• overfired burner

Smoke (only fuel oil burners)

Smoke in flue gas indicates poor burner performance. The amount of smoke can be measured with a smoke tester where smoke particles set on a filter paper are interpreted according a Bacharach scale.

Smoky combustion can be caused by

• soot formation on the heating surfaces
• insufficient draft, incorrectly adjusted draft regulator, improper fan delivery
• poor fuel supply, malfunctioning fuel pump
• defective firebox
• oil-burner nozzle defect, wrong size
• excessive air leaks in boiler or furnace
• wrong fuel-air ratio

Stack Temperature

The "net stack temperature" is the difference between the flue gas inside the chimney and the room temperature outside the burner. Net stack temperatures above 700^oF (370^oC) are in general to high. Typical values are between 330 - 500^oF (160 - 260^oC).

High stack temperatures may be caused by

• undersized furnace
• defective combustion chamber
• incorrectly sized combustion chamber
• excessive draft
• overfired burner
• draft regulator improperly adjusted
• soot formation on the heating surfaces

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Related Topics

• Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency

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