Chimney Flue Liners:
Metal liners are used to vent appliances through existing masonry
chimneys. The type and compound of metal is determined by the fuel.
Liners can be rigid or flex, insulated or not, depending on the chimney
itself, and the appliance requirements. The size of the liner is determined by the appliance, you can
not change the size of the vent (For example a wood stove with an 8"
outlet cannot be vented through a 6" liner. However it is often necessary to downsize an oil liner.)
The most common reason for using a liner is when venting a fireplace
insert or hearth stove. According to National Fire Code, which is NH Fire Codes, most fireplace flues are too large to properly vent an
insert or hearth stove, leading to creosote buildup and chimney fires. A pipe that goes
through the damper and up a few feet into the chimney, then stops, is
not a properly lined chimney, is not an NFPA 211 legal installation, and hasn't been since 1987.
Any new installation must conform to current codes, this includes
changing out of similar appliances (installing a modern wood stove to
replace an old one for example). Old installations should be upgraded
to meet current standards for safety reasons. This applies to oil flues
as well, modern oil furnaces produce a much more corrosive exhaust which
can really damage clay flue tiles. Remember the fire codes are written
in hindsight, they study what caused chimney and home fires and write
the codes to prevent those occurrences. So if something is "against
code" that means that it is known to cause fires and/or burn down
houses. You never want to go against fire code, or hire someone to do an
installation who doesn't know and follow the fire codes. In addition,
your insurance company does not have to cover any damages caused by a
non code installation.
A properly lined chimney is safer and functions better. Metal Chimneys are not chimney
liners but a separate unit with different requirements. Stove pipe can not be used as a chimney or chimney liner. It is only used to connect the stove to the venting.
We will not used poured liners due to their high failure rate. (see Bad Ideas Gallery and Inspections for pictures)
Poured liners are porous, so they absorb the acidic
condensate in flue gases and deteriorate. Also the industry discovered 20 years
ago that with modern appliances, which throw less heat into the flue, that low
thermal mass flues work better. Poured liners have a large thermal mass
that has to be heated up for the chimney to function correctly.
Once you put a poured liner in a chimney when it fails
removal usually requires the complete demolition of the chimney. If a metal
liner fails (which is very infrequent) it can usually be easily removed and
have also seen a large number of poured liners that have failed. Our
opinion is based on decades of experience and thermal science.
Spray on "sealants" are just that, a thin coat of sealer that is not a chimney liner.