When a gas furnace lacks the necessary primary air, what gases are still present in the fuel gas?

When a gas furnace does not have sufficient primary air, it results in incomplete combustion of the fuel gas. This incomplete combustion process leads to the formation of several combustion byproducts, primarily carbon dioxide (CO2) and carbon monoxide (CO).

Carbon dioxide is a natural product of complete combustion, where the fuel reacts fully with the available oxygen. However, when there is inadequate primary air, some of the carbon does not fully oxidize to CO2. Instead, it partially oxidizes to carbon monoxide, which is a colorless, odorless gas that is toxic and indicates inefficient combustion.

Thus, in a scenario where a gas furnace lacks the necessary primary air for optimal combustion, both carbon dioxide and carbon monoxide are present as a result of this incomplete combustion process. Therefore, recognizing the presence of both gases is crucial for assessing the combustion efficiency and safety of the furnace.