Flexible Metal Liners

There are two distinct types of flexible metal liners available and it is very important to distinguish between them.

SOLID FUEL LINER. This is a double skinned liner made from an extremely high quality stainless steel, usually 904L or 316Ti (Titanium) grade. It is smooth on the inside, corrugated on the outside and must be installed the correct way up. It is specifically designed for relining flues for solid fuel and wood. Whilst stainless steel is a very tough material, Its anti corrosion properties are also reduced if heated above 900ºC for more than about 15 minutes, perhaps as the result of a chimney fire.

GAS FLUE LINERS. A light gauge single skin liner, only suitable for closed gas fires and boilers, some inset fuel effect gas fires. It should never be used with solid fuel or wood burning appliances.

Flexible liners are relatively easy and clean to install. They are usually drawn down the chimney by rope from the top and will pass round most bends without opening up the flue. Support is provided by “hanging” the liner from a clamp or plate mounted at the top of the chimney. It should also be firmly clamped at the base before forming the connection to the appliance or flue pipe. Unlike rigid pipe, expansion and contraction will be taken up by the flexible construction of the pipe itself.

The solid fuel liner may be left with an air space as insulation. This may be satisfactory for open fires with relatively high flue gas speeds and temperature which will reduce the likelihood of condensation. A better solution is to back fill around the liner with a loose fireproof insulation material such as Perlite, Vermiculite or Leca granules. Some systems offer an insulation wrap, well suited to the large voids found in inglenook situations where back filling would be impractical. Insulation is essential with wood burning stoves due to the high incidence of condensation problems.

In all cases a small ventilation hole (usually 15mm) should be provided at the top of the chimney stack to allow any residual moisture to escape. Always follow the manufacturers installation instructions carefully.

Care should be taken when sweeping flexible metal liners as the use of an incorrect brush can damage the inner skin.

Only polypropylene brushes of the correct diameter and with a plastic ball top should be used. Where possible always use a member of the Northern Ireland Association of Chimney Sweeps who will be trained in the techniques required.

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