What are flue gases composed of?

Flue gases consist mainly of combustion products, which include carbon dioxide, water vapor, nitrogen oxides, sulfur oxides, and sometimes unburned hydrocarbons, depending on the fuel used and the combustion efficiency. The process of combustion in boilers or heaters generates these gases, along with excess air that was utilized for optimal burning conditions. This excess air helps ensure that the fuel burns more completely, thus influencing the composition of the resulting flue gases.

By emphasizing combustion products and the role of excess air, this choice captures the complexity of flue gases in real-world applications. It highlights how the mixture results from both the fuel being burned and the air supplied for efficient combustion, rather than focusing on singular components or incomplete aspects of the combustion process. Understanding this composition is crucial for assessing the efficiency and environmental impact of heating systems, particularly in plumbing and HVAC applications.