This document specifies the characteristics of performance for rigid or flexible metal flue liners, rigid metal connecting flue pipes and their fittings used to convey the products of combustion from appliances to the outside atmosphere (including their supports) or the chimney. This document specifies sootfire resistant flue liners, connecting flue pipes and fittings for combustion appliances burning solid, liquid and gaseous fuels and non-sootfire resistant flue liners, connecting flue pipes and fittings for combustion appliances burning liquid and gaseous fuels only. NOTE This means that flue liners, connecting flue pipes and fittings designated "O" are not suitable for combustion appliances burning solid fuel. Vitreous enamelled connecting flue pipes are also covered by this document. Rigid flue liners can be used as flue liners for renovation or adaptation of existing chimneys and as flue liners of custom built chimneys. Flexible metal flue liners described in this document are exclusively for renovation or adaptation of existing chimneys. Flexible connecting flue pipes and extensible flexible products designed to be compressed or extended along their length are excluded from the scope of this document. Single-wall and multi-wall system chimney products (chimney sections, chimney fittings and terminals, including supports) are covered by prEN 1856-1:2021, even if used as liners for existing chimneys or connecting flue pipes.