Why ventilation matters
An active flue needs airflow for safe, efficient combustion, while a disused flue still needs some ventilation to prevent condensation and damp building up inside the chimney breast.
Signs of poor ventilation
A smoky room when the fire is lit, or damp patches and a musty smell from a disused chimney breast, are both signs the flue isn't ventilating properly.
Getting the balance right
Whether it's a vented cap on a disused flue or checking an active flue's airflow, the goal is always the same — keep water out while letting the chimney breathe.