National Home Inspector Practice Exam

What is the most common cause of chimney flue liner deterioration?

1. Rust

2. Condensation

3. Bad cement

4. High wind

The correct answer is: Condensation

Chimney flue liner deterioration is primarily caused by condensation. This phenomenon occurs when warm, moist air from combustion gases meets the cooler flue liner, leading to the condensation of water vapor. Over time, this water can corrode and damage the materials of the liner, especially if the liner is made from metal or has insufficient insulation. The acidic byproducts of combustion, particularly in wood-burning and coal-burning appliances, can further exacerbate the deterioration process. This highlights the importance of ensuring proper venting and maintenance of chimneys to mitigate condensation and prolong the life of the flue liner. Rust is also a concern but is typically a consequence of the deterioration from condensation rather than a primary cause. Similarly, bad cement can lead to structural issues or less effective sealing but is not the predominant cause of the flue liner’s deterioration. High winds, while they can cause physical wear and tear on the chimney structure, do not directly cause the breakdown of the flue liner in the same manner as condensation does.