The Navien flexible flue liners are a type of chimney lining system designed to safely vent the exhaust gases from a boiler through an existing chimney. 

This provides a safe pathway for the exhaust gases, preventing them from leaking into the living spaces, and enhances the draft of the chimney, improving the efficiency of the boiler.

The Navien flexible flue liners also shield the interior of the chimney from the corrosive effects of the exhaust gases, prolonging its life.

This comes with a straight celling plate where the flue goes up under the chimney breast to take the flexible liner up the chimney.