Flue gas losses: how they are calculated and what they indicate about efficiency

Flue gas losses represent the percentage of heat that leaves the system through the chimney instead of being transferred to the water or the process.

Key data

For the estimation, the flue gas temperature, the combustion air temperature, and the O₂ or CO₂ content of the flue gases are typically used.

What increases losses

High flue gas temperature and excessive excess air increase the heat discharged into the chimney.

What an increase indicates

It may be related to a dirty heat exchanger, incorrect combustion settings, or a change in operating conditions.

Proper assessment

Losses should be compared with historical measurements and manufacturer limits, rather than being evaluated in isolation.