Flexible Stainless Steel Liners
Flexible stainless steel liners are the most commonly used in the UK. The lining is one-piece and is used in rolls of up to 30m lengthwise but cut to suit the flue needing work. It is quick to set up and less disruptive for the property owner.
Here are the advantages: no joints to leak except at the top and bottom; the internal diameter is fixed; fitting is easy and not disturbing to decorations; no set skills or equipment are needed and it is cost effective. The lining also has a small thermal mass which reduces condensation building up after the first fire and it quickly warms up and cools down.
The disadvantages are that stainless steel liners last up to 10 years so a new lining will be needed whenever the appliance - stove etc - is changed, following building regulations. Slow burning caused by solid smokeless fuel can even reduce the life expectancy to five years, so a non-metallic liner system would be better.
Property owners should also be aware that the steel liners are delicate and more prone to damage if they get clogged up with soot or tar and need cleaning. A flawless chimney flue and stack is needed, for that reason, without any structural issues – unless proper repairs are done. The liners are not a cheap alternative if the flue is damaged and they need complete replacement following any chimney fire. Again, the key message is: safety must come first.
Two types of flexi liners
There are two types of flexi stainless steel liners. A single-skin type, often known as a class 2 liner, is the cheaper model with one skin used on the inner and outside surfaces. It should never be used with a solid fuel appliance, only with those that burn oil or gas for temperatures ranging 250°C to 260°C and sometimes 300°C. If in doubt, check the liner rating with a certified and professional chimney sweep.
The second type is the double skin liner used for appliances giving a heat intensity of more than 300°C or appliances burning solid fuel. Two metal parts are used in the inner and outside surfaces and the grade and thickness may differ. The outer corrugated layer reinforces the lining strength and the inner section is smoother and more acid-resistant.
Flexi stainless steel liners may be a more convenient option but make sure the installation is properly done by a professional. Liners should be in excellent condition before being used and put in place the right way round in the chimney flue. Instructions given by the manufacturer should be strictly followed.
Common guidelines include checking the flue is big enough for the liner either via a core ball test (seeing if a ball larger than the flue can pass down easily) or testing the length with extra liner material. Installation should only happen if the liner is in perfect condition.
A rigorous flue sweep removes any soot and other deposits before the liner is tested and then put in place. Then the chimney pot will be removed for the liner to be lowered the correct way up from top to bottom with a nose cone for protection. The liner must fit snugly inside the flue and connected properly to the appliance using clamps to support the liner. A relevant connector is screwed to the liner base and supported with either a clamp or a debris plate. Debris plates are usually attached to the wall of the flue, and sealed if solid fuel will be burnt by the appliance.
Liners are either insulated or ventilated depending on the manufacturer’s instructions. Ventilation requires special vents to be fitted and insulation might be needed to block the gap between the flue wall and the liner. Types of insulation will depend on the liner manufacturer. Any loose insulation (e.g. expanded clay beads or vermiculite) must be dry and cement-free. Always refer to the manufacturer’s guidelines, if in doubt.
Finally, the liner will need a top plate fixed at the top, and sealed properly, as well as a clamp and the material should be pulled tightly with 75mm showing above the plate. Liners for solid fuel appliances will need more material halfway up the chimney pot as well - possibly with an extra clamp. Make sure the top of the chimney stack is watertight with the closure plate to prevent damp issues. Check the manufacturer’s instructions especially if fixing liners for gas or solid fuel appliances; to be sure the liner is fitted correctly at the chimney top. Chimney stacks must always be waterproof treated whenever a flexi stainless steel liner is put in place for any combustion appliance.
Once the liner is installed, a professional test is needed to comply with Building Regulations and a notice plate fitted alongside the production of a report by the chimney professional.