Analytical · Glossary
What is Excess Air?
% above stoichiometricAnalytical
Excess air is the air supplied to a burner beyond the theoretical amount needed for complete combustion.
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Excess Air Explained
Some excess air ensures complete burning; too much carries heat up the stack and wastes fuel. Oxygen trim control keeps excess air low and safe.
Excess air is estimated from measured oxygen in the flue gas.
Excess Air Formula
EA % ≈ O₂ ÷ (20.9 − O₂) × 100
| O₂ | dry flue gas oxygen (% vol) |
Example: 3 % O₂: EA ≈ 3 ÷ 17.9 × 100 ≈ 17 %.
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Calculators for Excess Air
Frequently Asked Questions
What is Excess Air?
Excess air is the air supplied to a burner beyond the theoretical amount needed for complete combustion.
What excess air is typical?
Gas burners often run with about 10 to 15 %, oil and coal higher; follow the burner maker.
Is the formula exact?
It is a good approximation for most fuels.
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