Which situation is a direct result of not having adequate combustion air?

Not having adequate combustion air in a heating system can lead to several critical issues that impact both efficiency and safety. When combustion air is insufficient, the fuel does not burn completely, which can lead to increased emissions. This occurs because the incomplete combustion produces excess carbon monoxide and unburned hydrocarbons, contributing to pollution.

Additionally, scorch marks on burner access doors can result from improper combustion, as flames may become unstable and create higher temperatures in localized areas. This overheating can cause discoloration or scorching on surrounding materials due to the excessive heat being generated in an attempt to maintain the desired temperature output with insufficient air.

A shift in flame color is also a significant indicator of inadequate combustion air. A normally balanced flame will show a consistent blue color, which indicates efficient combustion, while a yellow or orange flame can indicate that incomplete combustion is occurring, often leading to soot production and further inefficiencies.

Therefore, each of these outcomes—increased emissions, scorching on burner access doors, and flame color shifts—can occur as direct consequences of inadequate combustion air, making it clear that the correct answer encompasses all of these possibilities.