Several chimney flues rising out of a few chimneys along the skyline

Chimney Flue

Originally contributed by Jeff Butler • last updated 1/21/2021

On the outside, chimneys are often admired for being well-designed, formidable structures. But don’t let their appearance fool you because, as the old saying goes, “it’s what’s on the inside that counts.” And, the inside of a chimney is called the flue.


If the chimney is the visible masonry structure rising out of the firebox through the roof to the exterior of the home, the flue is the open-air space inside the chimney that vents hot air, smoke, and gases from the fire to the outside. As the hot air rises through the flue to the exterior of the home, it draws cooler air from the interior of the building through the firebox back into the flue. Airflow plays an important role in controlling the temperature of the fire and overall heat retention, and is typically regulated by dampers, which open and close to allow more or less air to move through the flue.

What Is A Chimney Flue Liner And Is It Necessary?

Despite being strong masonry structures, chimneys are not damage proof. That’s why, to help protect your chimney, it’s highly recommended (and mandated in some areas) that you install a chimney flue liner:

  • Chimney flue liners (commonly referred to as chimney liners) are protective coverings that line the inside of the flue to create a conduit to carry away hot air, gases, and smoke. They also help with efficiency by creating the proper vent size and airflow.
  • Although, not all areas have the same regulations, chimney liners are required by law in many places. Be sure to check requirements for your location.