A chimney liner or flue liner only needs to be replaced if it is no longer working properly.
If you have had a chimney fire in your stainless steel liner it will need to be replaced before the chimney can be safely used again. This is because the extreme temperatures endured during a chimney fire change the structure of the stainless steel and it will no longer be fit for purpose.
Sometimes the existing flue is simply far too large for modern appliances, but the main reason is that many old chimneys will fail the smoke test, which means that the flue is leaking smoke and fumes into the building.
If you have a modern, efficient wood-burning stove, you will require a Class 1 flue liner that is normally made of stainless steel. Flexible 316-grade stainless steel liners are the most popular lining for an existing chimney as they are the most cost-effective and the work can usually be carried out in one day or less with little upheaval or mess.
A stainless-steel liner installed correctly will last many years, and they are often guaranteed for 10 years or more.
Gas stoves only require Class 2 flue liners, which are much cheaper, and lighter, yet still, meet safety regulations.