An object placed in an appliance to change the direction, extend the path, or slow the flow is called a:

The term that best describes an object placed in an appliance to change the direction, extend the path, or slow the flow is a baffle. Baffles are commonly used in various heating appliances, including fireplaces and wood stoves, to control the movement of smoke and gases. They help to optimize airflow, which can improve combustion efficiency while also allowing for better heat retention within the appliance.

Baffles are designed to redirect combustion gases and can contribute significantly to the overall performance of the heating device by enhancing its efficiency and reducing the emissions of harmful substances. They achieve this by effectively managing how gases flow through the system, allowing more complete combustion and thus a safer operation.

In contrast, while dampers, chimney caps, and flues play important roles in the functioning of chimney systems and combustion appliances, they serve different purposes. Dampers control airflow and can be adjusted to regulate the draft. Chimney caps prevent rain and debris from entering the chimney and keep animals out, while flues are the passages within which the combustion gases travel, providing a path for those gases to escape to the outside.