As the temperatures and air density in boiler rooms change, the combustion will vary slightly. O2 Trim senses these changes by measuring the oxygen in the exhaust of the boiler and sending a message back to the servo control system, which will then correct for the changes. These precise adjustments significantly reduce the amount of fuel needed to fire the boiler over time, resulting in energy savings as well as increased operating efficiency.
A more costly, but also more comprehensive, version of O2 Trim is the Autoflame EGA (Exhaust Gas Analyzer). The EGA can monitor multiple different types of levels at a time, including CO2, NOx and O2, a valuable investment for those interested in constant monitoring of all types of emissions.