What is uncontrolled air that leaks into the combustion area referred to as?

Uncontrolled air that leaks into the combustion area is referred to as tramp air. This term is used in heating and combustion contexts to describe unintentional air infiltration that can disrupt the proper air-to-fuel ratio needed for efficient combustion. Tramp air can lead to issues such as incomplete combustion, which may result in increased emissions and reduced efficiency of the heating system.

In contrast, fresh air specifically refers to air that is drawn into the combustion process to support efficient burning, while combustion air is the air that has been specifically measured and controlled for optimal combustion. Exhaust air is the byproduct of combustion that is expelled from the system. Thus, tramp air emphasizes the issues arising from uncontrolled infiltration rather than the controlled aspects of combustion air needed for proper operation.