Flue Gas Oxygen Calculator

The Number on Every Combustion Analyzer Readout

Flue gas O2 percentage is the most commonly checked combustion tuning indicator, since it's directly measurable with a portable analyzer and tracks closely with excess air level.

The Formula

O2% = (20.9 × Excess Air%) / (100 + Excess Air%)

20.9% is the oxygen content of dry ambient air.

Worked Example

A burner running with 15% excess air:

O2% = (20.9 × 15) / (100 + 15) = 2.73%

How to Use This Calculator

Enter the Excess Air percentage.
Select Calculate to get expected flue gas O2%.

Related Calculations

Need excess air from a measured O2 reading instead? See the Excess Air Calculator, or check CO2 percentage in the Flue Gas CO2 Calculator.