What is the definition of flue gas?

Flue gas refers to the gases that are generated as a byproduct of combustion processes, primarily in heating systems like boilers, furnaces, or engines. When fuels are burned, the reaction produces a mixture of gases that contains not only the combustion products like carbon dioxide and water vapor but also includes any residual inert gases and, in some cases, unburned portions of the fuel, along with excess air that was mixed during the process.

The definition captures the comprehensive nature of flue gas as encompassing all emissions resulting from the combustion, rather than isolating it to just one kind of gas or categorizing it solely based on a specific property. This is crucial for understanding flue gas's implications in HVAC systems, as it helps in assessing not only the efficiency of combustion but also the potential environmental impacts and regulatory considerations related to air quality.