A chimney lining is made out of nonflammable material and lines the inside of the chimney. All fireplaces and fuel-burning equipment, such as gas stoves and furnaces, require some type of chimney. Chimneys must provide enough draft to supply an adequate amount of fresh air to the fire which will then expel the smoke and gasses that are emitted by the fire. To help in this process, a chimney lining is necessary. A chimney lining should be smooth, clean, and non-porous so that it is easily cleaned and moisture resistant. The liner should be at least the size of the opening that connects the fireplace, stove, or furnace to the chimney. Because smoke and heat travel upward in a spiral motion, a round shape is most desirable. If a round liner is not available, a square or rectangular shaped liner with rounded corners is more efficient than a liner with sharp corners. Any space between the liner and the outer wall should be dead air space rather than circulating air. For more information about chimney liners, contact your local heating professional.