A flue liner is a protective lining installed inside a chimney to improve safety and efficiency. It helps direct smoke and gases from a fireplace or furnace safely outside, preventing harmful substances from entering the home. Flue liners can be made from various materials, including clay, metal, or concrete, and they also help to protect the chimney structure from heat and corrosion. Installing a flue liner can enhance the performance of heating appliances, such as wood stoves or gas furnaces, by ensuring proper ventilation. Additionally, flue liners can reduce the risk of chimney fires by containing creosote buildup, a flammable substance that can accumulate in chimneys over time.