The chimney that you see exiting above a house is only the exterior portion of a system that is extremely important to the safe operation of fireplaces and other appliances that burns fuel inside the home. The chimney is the support structure for the flue. The flue is a lining inside the masonry that is designed to carry products of combustion safely from the point of combustion to the outside atmosphere.
For safe operation, it is imperative that the inside walls of the flue be sealed from top to bottom so that no gases or other fluids can leak into the surrounding chimney structure or into the building from inside the flue. If the terra cotta flue is not in perfect condition, carbon monoxide can easily enter the living quarters. Cracks in the flue can also allow intense heat and flames to escape into the wooden home structure, sometimes causing destructive and lethal fires. For all of these reasons, all chimneys should have a stainless steel chimney liner installed inside the flue.
Chimneys built before the 1940’s relied upon the bricks and mortar to keep the exhaust gasses from entering the home, there was no flue lining inside the brick work. Since the 1940’s, chimneys have been built with a terra cotta chimney liner installed as part of the construction process. This was originally designed for use with coal stoves, not the high efficiency oil and gas appliances we have today.
A regular inspection of a chimney to check for cracks in the bricks, mortar, or clay tile liner is necessary to ensure safe operation of the chimney system. If the inspection reveals damage to the inside of the terra cotta flue, the chimney should not be used until a stainless steel liner is installed, making the chimney safe again.
A stainless steel chimney liner is air tight, preventing any carbon monoxide from ever entering the home. They can also contain a chimney fire, if installed properly, with no damage being done to the home.