Double Wall Liner Vs. Insulated Flue Liner

Double Wall Liner

• A double wall liner has an outer pipe and an inner pipe with a gap of up to 1 inch in between the two pipes. The pipes are made of flexible or rigid stainless steel or aluminum. The two pieces are welded or clamped together to form one piece. Double wall liners are typically used in masonry chimneys. They connect to the ventilation opening on the back of the stove or top of the fireplace and extend to the full height of the chimney. Flexible double-walled liner can be cut and used as an elbow piece to connect to the stove or fireplace and then to a long rigid liner piece that runs vertically up through the chimney.

Insulated Flue Liner

• Insulated flue liners are typically made of metal or clay. The insulation material wraps around the interior walls of the flue liner and is typically made of a mix of vermiculite, pumice, cement and other heat-tolerant masonry materials. Liners add to the life expectancy of chimneys by protecting the masonry materials from combustion and help keep them from producing corrosive or toxic byproducts such as carbon monoxide. The insulation reduces condensation buildup inside the chimney. As a result, the chimney stays cleaner longer and you reduce the conditions for creosote to develop. Creosote is a byproduct of smoke and gases that forms as a soot or sticky substance that will coat the walls of an unlined chimney, or one that has a malfunctioning flue.

Similarities

• Like insulated flues, a double wall liner can also be insulated. This is done during manufacturing and the liner is sold with insulation already attached. The insulation on double wall liners is typically made from fiberglass insulation. It fits between the outer and inner stainless steel walls of the liner. If you need to figure out what type of liner is currently installed in your chimney, you will need to go on top of your roof and look down into the chimney. You will know if you have a double wall liner if you see two metal layers inside the chimney. Conversely, you will know that you have an insulated flue liner if you only see one metal or clay pipe layer and a layer of insulation surrounding the interior surface of the flue liner.

Differences

• Insulation is optional with double wall liners. You can purchase a double wall liner with an interior and exterior stainless steel wall and no lining. Units without insulation are referred to as double wall air-insulated liners. Manufacturers connect the two liner surfaces together with clamps so the liner unit works as one solid piece. And when you make a change, such as converting from a wood-burning fireplace to gas, you may have to change the type of liner you use. Always follow manufacturer recommendations and local building code requirements before you install any type of liner.