Which of the following is an effect of improper combustion air supply?

Improper combustion air supply can lead to the production of harmful gases, making this the correct answer. When there is insufficient air for the combustion process, fuel may not burn completely. This incomplete combustion can result in the generation of hazardous byproducts such as carbon monoxide, unburned hydrocarbons, and particulate matter. These gases can pose significant health risks to occupants in a building, leading to poor indoor air quality and increased risk of respiratory issues or other health effects.

On the other hand, reduced energy consumption, increased fuel efficiency, and improved indoor air quality suggest a scenario where combustion processes are functioning optimally with adequate air supply. In cases of improper air supply, it is more likely that energy efficiency would decrease rather than improve, as incomplete combustion often leads to wasted fuel. Thus, the presence of harmful gases is a crucial concern when assessing the effects of improper combustion air supply.