Which instrument is most appropriate for calculating carbon dioxide levels in flue gas?

The most appropriate instrument for calculating carbon dioxide levels in flue gas is a combustion analyzer. This device is specifically designed to measure the concentrations of various gases, including carbon dioxide, in the exhaust of combustion appliances like gas furnaces.

Combustion analyzers work by sampling the flue gas and providing real-time readings of the concentrations of gases such as carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), and others. This information is crucial for assessing the efficiency of combustion and ensuring safety in gas appliances, as high levels of carbon dioxide can indicate poor combustion, leading to increased fuel consumption and potential hazards.

In contrast, the other instruments listed have distinct functionalities. A manometer measures pressure levels, which does not directly correlate to gas concentrations. A digital multimeter is used for measuring electrical parameters and does not measure gas levels. Meanwhile, a smoke test kit is employed to check for drafts and the presence of smoke, but it doesn't provide quantitative data on gas content. Thus, the combustion analyzer stands out as the most fitting choice for monitoring carbon dioxide in flue gas.