Using a mirror and flashlight to view the heat exchanger on a gas furnace allows the inspector to see _________ heat exchanger.

Using a mirror and flashlight to inspect the heat exchanger on a gas furnace typically allows for a limited view of the component. This approach can help the inspector see only a fraction of the heat exchanger, often less than 20%. The design and placement of the heat exchanger in gas furnaces can make it difficult to access or see without specialized tools. The use of a mirror and flashlight can illuminate certain areas and angles, but due to physical constraints and obstructions within the furnace, a complete or even mostly complete view is not feasible. This limitation underlines the importance of understanding the inspection techniques and the physical constraints when working with HVAC systems.