Q: We're about to buy a new wood-burning stove, and our local dealer refuses to install it unless we buy a stainless steel liner that goes all the way
out the top of the chimney. Do we really need to do this? If so, is it something we can do ourselves?
A: There are four situations relating to your existing chimney that would cause your code authority to require a stainless liner for a wood
1) The existing chimney is unlined. In the past, some masonry chimneys were built without any liner at all. Without a liner, wood exhaust can leak
through the mortar joints into the house. Further, liquid creosote will eventually dissolve the binder in the mortar and soak into the joints, until the
chimney itself could catch fire!
2) The existing chimney is lined, but the liner is cracked or damaged. Masonry chimney liners are made of clay or pumice, which can crack from
chimney fires, settling, or other causes. Cracks in a pumice or clay flue liner will let the smoke and liquid creosote through, leading to the same
problems described above.
3) The existing chimney is lined, but the liner is too large. Oversized flues cause numerous problems, like smoke spillage into the house when
they're cold, stove overfiring when they finally heat up, and the kind of excessive creosote formation that leads to chimney fires. Code prohibits
venting any woodburner into a chimney flue with a cross-sectional area (CSA) that is more than three times the CSA of the flue collar on the stove.
Thus, if your stove has a 6" flue collar (28 sq.in. CSA), the chimney flue must have a CSA less than 84" (3 x 28). In other words, if the chimney flue
is larger than 10" round (78 sq.in. CSA) or 9" x 9" (81 sq.in. CSA), you must install a 6" stainless liner. This rule gets tougher if one or more of the
chimney surfaces is on an outside wall, so it is exposed to outdoor temperatures for its entire length: in those cases, the CSA of the flue can't be
larger than two times the CSA of the flue collar, so you must reline if the existing flue is larger than 8" round or 7" x 7".
4) The existing chimney is air-cooled, like the manufactured metal chimney
used for zero-clearance wood fireplaces. Cooling the exhaust from an airtight
woodstove leads to balky updraft, smoke spillage and excessive creosote formation.
Code requires installation of an insulated liner to eliminate those problems.
Our Forever Flex liner kit for wood stove installations consists of a rain cap, a top plate, a length of flexible stainless steel pipe, a tee with bottom
cap and removable snout, and a tube of hi-temp silicone sealant to affix the top plate to the chimney. For pricing,
Installing a chimney liner doesn't really require much mechanical aptitude, and many of our online customers choose to do it themselves. Here's
Note: Each Code Authority chooses the standards that regulate appliance and chimney installation and usage in their jurisdiction, and may modify
code specs as desired. The above-referenced specification is from the Washington Association of Building Officials Woodstove Installation Code
Book and NFPA 211, and may not reflect the code requirements in your area. Contact your Code Authority for local regulations.
Manufacturers who submit an appliance to a recognized laboratory for safety testing may receive a specific venting listing for that appliance which
may be accepted by your Code Authority in lieu of the standard code requirements. These listings are unique to each model, and can be found in the
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