Work out flue gas analysis instantly with clear inputs, formula shown and shareable results.
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.
Excess air
Excess air % = O2 / (20.9 - O2) x 100
Expected CO₂
CO2 % = CO2 max x (20.9 - O2) / 20.9
Preliminary estimate only. Combustion tuning must be carried out by a qualified technician with a calibrated analyser and a carbon monoxide check.
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).
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.
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.