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Fireplace & Hearth

Fireplace Flue

The fireplace flue is the interior passageway within the chimney through which smoke, combustion gases, and heat travel from the firebox to the exterior atmosphere. It is the functional core of the chimney system, and its dimensions, condition, and liner material directly impact the draft strength, efficiency, and safety of the fireplace. A properly sized and maintained flue creates the upward draft necessary to draw smoke away from the living space while pulling fresh air into the firebox for combustion. Flue sizing is governed by building codes and must be proportional to the fireplace opening to create adequate draft without excessive air loss. An undersized flue results in poor draft and smoke spillage into the room, while an oversized flue can cause sluggish draft and excessive cooling of combustion gases, leading to increased creosote formation. The flue should be as straight and vertical as possible, as bends and offsets reduce draft efficiency. Regular professional cleaning removes creosote deposits that not only reduce airflow but also present a serious chimney fire hazard.

Key Characteristics

  • ✓Interior passage channeling smoke to the exterior
  • ✓Dimensions must be proportional to fireplace opening
  • ✓Condition directly affects draft and safety
  • ✓Requires regular cleaning to remove creosote
  • ✓Should be as straight and vertical as possible
  • ✓Lined with protective material for safety

Types & Variations

Clay tile lined flue
Stainless steel lined flue
Cast-in-place concrete lined flue
Unlined historic flue requiring upgrade
Insulated double-wall metal flue

Common Materials

Clay terra cotta flue tilesStainless steel flexible or rigid linerCast-in-place refractory cementHigh-temperature insulation wrapAluminum liner for gas appliances onlyVolcanic pumice composite blocks

Works Well With These Styles

TraditionalRusticCraftsmanColonialFarmhouse

Placement & Usage Tips

The flue is a structural element that must be properly sized during construction or renovation. Each fireplace or heating appliance should have its own dedicated flue to prevent cross-contamination of exhaust gases.

💡 Pro Tip

Schedule annual flue cleaning before the burning season begins, not after it ends, so any issues discovered can be repaired before you need to use the fireplace. A level two inspection with video camera is recommended when buying a home or after any chimney event like a lightning strike.

Related Terms

Chimney

A vertical structure containing one or more flues that channels smoke, gases, and combustion byproducts from a fireplace or stove upward and safely out of a building.

Fireplace Damper

A movable metal plate or valve located in the flue or throat of a chimney that can be opened to allow smoke to escape during use or closed to prevent heat loss when the fireplace is not in operation.

Fireplace Liner

A protective lining installed inside a chimney flue, made from clay tile, stainless steel, or cast-in-place concrete, that protects the chimney walls from heat and corrosive byproducts.

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