Old chimneys were built without flue liners. The mason simply applied a layer of plaster to the inside of the chimney as he built it. If you have an old chimney that’s in need of repair, consider adding a flue liner instead of rebuilding the chimney. The former approach is much less expensive than the latter. Also, if your chimney has no liner, adding one will strengthen the chimney and provide some insulation.
Don’t expect a flue liner to prevent creosote buildup. The creosote will simply form on the walls of the liner.
Depending on how frequently you use your chimney and how hot a fire you burn, you may want to use a stainless steel liner in your old unlined chimney. To install the liner, hook the sections together and lower them down the chimney. Stainless steel liners will burn out in time, so they’re most effective if you don’t have a lot of very hot fires.
If you want to reline a chimney that isn’t straight, poured concrete is about the only material you can use. Old houses frequently have corbeled chimneys, where the mason moved part of the chimney a few inches to dodge a rafter. Before pouring a concrete flue liner, the contractor will stuff a giant balloon down the chimney as a form for the concrete. This balloon and the concrete can bend with the chimney. Metal flue liners will accommodate some bends, but poured liners are more versatile.
If your chimney is used for a stove and you’re considering relining it with poured concrete, be sure to double-check the size of the flue before proceeding. A poured concrete liner should be at least 1″ thick all around, and the remaining flue area should be no smaller than about 40 square inches. (For a round flue, that translates to about 7″ in diameter.) Make sure your flue is large enough to meet these requirements. If it’s not and the liner consumes too much space in the chimney, the draft will be cut back, causing smoke to escape into the room.
If you have a poured-concrete flue liner installed in a chimney that leads to a fireplace, make sure that the concrete is stopped at the bottom of the flue and does not fill up the chimney’s smoke shelf. (You can make an exception if you have a wood stove hooked up into your fireplace and don’t plan to use the fireplace without the wood stove again.)
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