Combustion analyzers are instruments commonly used to measure the efficiency and proper operation of liquid, gaseous or solid fuel boilers (oil, natural gas, wood, biomass, etc.). These devices produce heat to warm water or air in a heating system. 
 
A flue gas analyzer is also used to measure the combustion levels in an internal combustion engine, such as those used in cars, trucks, tractors, generators (gensets) and other motorized equipment.