Operation & Optimization4 / 10
Managing Excess Air
The balance between combustion completeness and flue losses.
9 min read · Jacob Willis, Net Zero Lead · Last reviewed July 2026
You need excess air to burn fuel completely. But more is not better. Too much excess air wastes energy up the flue; too little leaves CO and incomplete combustion. The art of boiler tuning is finding the sweet spot.
In this lesson
- 01The efficiency penalty of excess air
- 02Why we run excess air anyway
- 03Tuning the air/fuel ratio
- 04Lambda and oxygen trim
- 05Practical tuning: a checklist
- 06Sources and further reading