Flue lining and condensation issues

The fitment of a flue liner can restrict airflow through a chimney and reduce or fully eliminate the naturally occurring updraught that reduces the potential for condensation forming within the stack.

Condensation forming within a chimney can present as dripping (black) water within a fireplace or can also mobilise hygroscopic salts within masonry, that present on internal chimney breasts as damp or wet patches.

At least one chimney pot should be left open, and where this is not possible, vented steel spacers can be fitted beneath the vented cowl to allow airflow through the chimney pot.

Vented cowls are both fine to use and recommend. The issue being highlighted only occurs when a flue liner is connected to the cowl base, effectively sealing the rest of the chimney and preventing updraught.