Chimney Flue

A chimney flue is a vertical channel within a chimney structure that carries combustion gases and smoke from a fireplace, stove, or boiler safely out of the building. The flue creates a natural draft — warm gases rise and draw combustion air into the firebox — which is essential for efficient burning and safe operation. Flues are constructed from brick, ceramic liners, or stainless steel, depending on the building and fuel type.

The flue is one of the most critical fire safety components in any home with a fireplace or wood stove. A properly functioning flue ensures that toxic combustion products — including carbon monoxide — are safely expelled from the building. When the flue is blocked, cracked, or deteriorated, these gases can leak into living spaces, creating a life-threatening hazard. The draft characteristics also affect combustion efficiency: a poor draft leads to incomplete combustion, more smoke, and faster creosote buildup.

Creosote and soot deposits accumulate on the interior walls of the flue during normal use. These deposits are combustible, and if they build up sufficiently, they can ignite and cause a chimney fire — an extremely dangerous event that can spread to the building structure. This is why chimney sweeping is required by law in Finland: regular cleaning removes deposits before they reach dangerous levels.

The flue should be inspected for cracks, deterioration, and creosote buildup as part of every chimney sweeping visit. If the chimney sweep reports concerns about the flue's condition, a more thorough chimney inspection may be needed. Common flue problems include cracked mortar joints, deteriorated liner sections, and damaged flue caps that allow rain and animals to enter.