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Flue Gas Analysis Calculator

Work out flue gas analysis instantly with clear inputs, formula shown and shareable results.

About Flue Gas Analysis Calculator

Residual oxygen in the flue reveals how much air was supplied beyond the stoichiometric requirement: excess air equals O2 divided by (20.9 - O2). The same dilution factor scales the fuel's maximum carbon dioxide down to the measured value, and net stack temperature, the rise above combustion air, drives the sensible stack loss.

Formulas

Excess air

Excess air % = O2 / (20.9 - O2) x 100

Expected CO₂

CO2 % = CO2 max x (20.9 - O2) / 20.9

Worked example

With the default values below, Flue Gas Analysis Calculator returns Excess air of 40.3%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Measured oxygenaccepts 0.1–20 %
6 %
Stack temperatureminimum 50 °F
400 °F
Combustion air temperatureminimum -40 °F
70 °F
Stoichiometric CO₂ for fuelminimum 5 %
11.7 %

Results

Excess air
40.3% %
Net stack temperature
330.0 °F
Expected CO₂
8.34% %
Dilution factor
1.403

Step by step

  1. 1Values used
  2. 2Excess air
  3. 3Expected CO₂
  4. 4Excess air= 40.3 %
  5. 5Net stack temperature= 330.0 °F
  6. 6Expected CO₂= 8.34 %
  7. 7Dilution factor= 1.403

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Combustion tuning must be carried out by a qualified technician with a calibrated analyser and a carbon monoxide check.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Combustion tuning must be carried out by a qualified technician with a calibrated analyser and a carbon monoxide check.

Frequently Asked Questions

How is the Flue Gas Analysis figure worked out?

Excess air % = O2 / (20.9 - O2) x 100. Residual oxygen in the flue reveals how much air was supplied beyond the stoichiometric requirement: excess air equals O2 divided by (20.9 - O2).

How little excess air is safe?

Gas burners normally run 15-30 percent excess air. Going lower risks carbon monoxide and soot because mixing is never perfect, so a safety margin is deliberate.

What values do I need to enter?

This calculator takes 4 inputs: Measured oxygen, Stack temperature, Combustion air temperature, Stoichiometric CO₂ for fuel. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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