A flue liner is an important component of any chimney due to its protective function and the fact that it contributes to the longevity of the chimney and any connected appliance. It also improves the safety profile of the chimney.

There are three vital reasons for having a flue liner. One is that the liner acts as a barrier against transfer of heat from the fireplace exhaust to the adjacent combustible structures in the house, such as wood scaffolding. An unlined chimney conducts this heat very well and causes ignition of adjacent combustibles in a short time. The liner also protects the chimney itself from corrosion by products of combustion. Gases in the flue (the space in the chimney) can penetrate and erode the brick and mortar making up the wall of the chimney, causing it to lose structural integrity. This also provides a conduit for the passage of toxic flue gases into the house.

The other major reason for having a proper flue liner is that it provides a snug fit to the connected appliance such as a wood burning stove. This ensures that no toxic gases leak into the house from the connected appliance. It also ensures that the connected appliance burns fuel more efficiently, as the snug fit promotes optimal air supply which guarantees efficient burning of fuel and lower noxious gas production.