Combustion analyzers and flue gas analyzers measure the gas content of flue gas in order to monitor the combustion efficiency of fuel-burning equipment. Combustion efficiency indicates how well fuel-burning equipment burns a fuel such as coal, oil, propane, and natural gas. Combustion efficiency calculations assume complete fuel stoichiometric combustion and account for fuel chemistry, the net temperature of stack gases, and the percentage of oxygen or total combustibles by volume after the combustion process. Combustion analyzers and flue gas analyzers measure these stack gases, which contain water vapor when hot and liquid condensate when cooled. Stack gas consists mainly of nitrogen, with oxygen, carbon dioxide and trace total combustible gases, and they should be measured before dilution occurs.

Combustion analyzers and flue gas analyzers are used to measure parameters such as individual gases flue-gas temperature, daft/differential pressure, combustion air temperature, and dew point. They are also used to measure levels of oxygen gas, carbon monoxide, carbon dioxide, nitric oxide, and sulfur dioxide. When selecting combustion analyzers and flue gas analyzers, industrial buyers should consider the number of gas components to measure, and the importance of measuring either with extractive or direct in-situ instruments. Some combustion analyzers and flue gas analyzers are suitable for sampling applications while others are designed to provide in-situ continuous measurements.

Combustion analyzers and flue gas analyzers can be used to improve boiler efficiency, enhance worker safety, improve air quality, supplement preventative maintenance programs, and save energy. Traditionally, products were large, relatively heavy, and enclosed in a metal case. They were equipped with analog displays, typically with mechanical components and a dial with a needle pointer. Modern combustion analyzers and flue gas analyzers are lightweight, handheld products that are designed for field use. They usually feature a plastic case and digital, alphanumeric display.

Features for combustion analyzers and flue gas analyzers include sensors, power supplies, purge pumps, field-replaceable thermocouples, communications capabilities, and built-in diagnostics. Some combustion analysis products are equipped with a thermal printer and integral software. Others have built-in microprocessors, hydrophobic filters that prevent the ingress of moisture, and audible alarms or visual indicators. Combustion analyzers and flue gas analyzers that can detect chlorofluorocarbon (CFC), hydrofluorocarbon (HFC), and hydrochlorofluorocarbon (HCFC) emissions are also available.