In terms of venting, how should a chimney be treated when replacing or installing a gas furnace?

When replacing or installing a gas furnace, it is essential that the chimney must be lined to ensure safe and efficient venting of combustion gases. Lining the chimney helps to create a proper pathway for exhaust gases to exit the building, reducing the risk of backdrafts or leaks that can pose safety hazards, such as carbon monoxide exposure.

A properly lined chimney also prevents the internal surfaces from deteriorating due to the corrosive nature of gas combustion byproducts, which can lead to structural issues over time. Furthermore, using a liner can enhance the efficiency of the venting system, improving the overall performance of the gas furnace.

In the context of other options, not lining the chimney could lead to serious safety risks. Removing the chimney entirely is usually unnecessary unless it is significantly damaged beyond repair, and simply insulating it does not address the fundamental need for proper venting. Thus, lining the chimney is a critical requirement in ensuring that the system operates safely and effectively.