NVS Limited

Chimney Liner Information

Single Wall Liners

  • Made from corrosion-resistant 316L stainless steel.
  • Leak resistant construction due to continuous weld (Wonderflex) or dovetail folded seam (Triplelock).
  • Highest corrosion resistance.
  • Deep corrugations for high crush resistance and better flexibility when installing.
  • Strong seam construction resists the rigours of pulling the liner into place during construction.

Twin Wall Liner

  • Both inner and outer layers made from corrosion-resistant 316L stainless steel. 904L stainless steel is also available as an option for the extreme conditions found with appliances like slumbering stoves.
  • Corrugated outer skin for high crush resistance.
  • Extra smooth inner skin allows for easy drain down of condensates, less opportunity for soot to collect in the joint area and ease of sweeping.
  • Inner skin remains overlapping to protect the joint from corrosion penetration even at minimum bending radius.
  • Inner skin remains smooth and protective even after the rigours of installation.

Mandatory requirements on acceptable chimney, flexible liner and appliance combinations.

Building Regulations Document J requires that a flexible flue liner can only be installed completely enclosed inside a masonry chimney. A non masonry enclosure such as timber or plasterboard boxing in is not acceptable. The type of flue liner permitted depends on the fuel to be used, the type of appliance and the type and year of chimney construction in which it is to be fitted. Building Regulations Document J, outlines different requirements for relining masonry chimneys built before and after 1st February 1966.

Termination methods recommended by BS7566 Part 4

For gas burning installations, a flue terminal is required that complies with section 5 of BS715. Where a proprietary terminal is not used, the free area of outlet openings on the termination shall be at least twice the cross sectional area of the flue. Outlet openings shall be such that they will admit a ball of 6mm diameter but not of 16mm diameter. The openings shall be uniformly distributed around the terminal or arranged at two opposite faces. (BS5440 Part I). An approved terminal should be used to protect the end of the flue. A gas flue terminal must be fitted to an all gas installations of 170mm diameter or less.

For oil burning installations, a rain cap or universal terminal may be used, however, as there is a corrosion risk on such systems, regular inspection is recommended.

Multi-fuel Applications, Rain caps and universal terminals are not recommended for use on solid fuels, as the use of covered terminals will increase flow resistance and encourage the formation of aggressive condensates and deposits. In some instances, a terminal incorporating a spark guard may be demanded to reduce the risk of fire hazard. For all multifuel systems, regular cleaning is essential to prevent the accumulation of material which could ignite and create a fire hazard.

Re-use of a previously capped or shortened chimney.

The chimney can be reused providing the existing brickwork is inspected to ensure it is in good condition. The chimney can be lined with the appropriate liner, ensuring that the liner is used only inside the stack. Connection to flue pipe, or to B Vent (gas), Eco ICID (multifuel) or ICS (multifuel) system can be made to the appliance/ termination, by using the appropriate connector inside the chimney, and suitably sealed with fire cement. The stack can be extended using ICS, B Vent or Eco ICID depending on the application.

Re-use of a fitted flexible liner when changing the appliance.

Provided the diameter and type of flex is suitable for the new appliance to be fitted and the installer has inspected the liner and is satisfied with its condition the liner can be reused. However, as the lifespan of the previous appliance and liner may not be known, it is strongly recommended the old flueliner is removed, the chimney swept, then a suitable new liner installed.

Use of flue liner on condensing appliances.

TecnoFlex can be used on condensing appliances, which have pressure at the flue outlet of 200Pa maximum. It is necessary to fit a tee and drain point at the base of the vertical system, adequately supported, and connected to a drainpipe to a suitable drain point.


Mandatory Requirements

Connection to an appliance which is not connected to the fuel supply, should be carried out by a competent person. However, connection to an appliance that is connected to the fuel supply must be carried out by a Gas Safe (gas), OFTEC (oil) or a HETAS registered installer.

Prior to installation

In all cases the chimney should be inspected for deterioration and if necessary any remedial work required should be carried out. The chimney should be swept, preferably by a member of NACS (National Association of Chimney Sweeps) or a suitably qualified chimney sweep who would provide a certificate after sweeping and checking, which should be retained for future reference. It will be necessary to check that the flaunching at the top of the stack is not cracked, and if so replaced. The brickwork pointing and the flashings should be checked to ensure they are in good order and corrected as necessary.

Installation of the liner

The flue liner should be pulled down the chimney using a nose cone and string/rope. All Wonderflex & Triplelock packs are supplied with a nose cone. In the case of TecnoFlex, a screw fit nose cone can be purchased and connected to the end of the TecnoFlex by screwing the cone onto the outside of the TecnoFlex. lt is strongly recommended that a 1m test section, with nose cone attached, is pulled through the chimney prior to installation in order to ensure the chimney is suitably sized, and free from obstructions. These can be purchased separately. When securing the liner to the clamp plate or clamp band, ensure 75mm of liner is protruding to secure the terminal.

Liner Orientation

It is essential in the case of twin wall TecnoFlex that the liner is installed the right way up. The arrow on the outside of the liner indicates the direction of flue gas flow and must be pointing upwards towards termination. Gas flex can be installed either way up.

Bending of the liner

Great care should be taken to avoid overbending or kinking the liner on installation.


If insulation is required, granules such as Vermiculite, should be poured in around the liner from the top of the stack after fitting a suitable debris plate at the bottom of the system. Alternatively a solid tube of high quality insulation can be used.

Support of the liner

Wonderflex and Triplelock are relatively light and can be supported at the top of the chimney using a clamp plate fixed to the top of the masonry stack. TecnoFlex however, is heavier and must be supported using a separate plate and clamp securely fixed to the top of the stack. Where a tee is used at the base of the system to provide a drain point/cleaning access or connection to a flue pipe from the appliance, a bottom support bracket is required, fixed to the inside of the stack. In all cases, liner lengths exceeding 20 metres should be provided with intermediate support.

Cutting the liner to the correct length for the chimney.

After the length of flue liner has been connected to the appliance, allow at least 75mm of liner to protrude above the clamp plate and cut. For Wonderflex & Triplelock, an industrial knife can be used. For TecnoFlex use metal snips. At all times extreme care must be taken when cutting the liner and strong industrial gloves plus long sleeved overalls should be worn as cut edges are very sharp. In addition, any tape secured to the ends of the liner, which is provided for safe handling prior to installation, must be removed before completion and commissioning of the full system.

Sealing the flue liner to the chimney pot.

The clamp plate or plate and clamp holding the liner to the chimney top should be fixed using screws and wall plugs. To weather the top of the chimney stack and seal any gaps between the liner installation and the chimney pot appropriate acid resistant mortar should be used.

Connection of the Terminal to the flue liner.

For gas and oil systems, the terminal should be fitted over the protruding 75mm of liner and rivetted or secured using self tapping screws. On TecnoFlex, where used on solid fuel appliances, a proprietary chimney pot must be fitted by bedding the pot on to the top plate.

Joining of flexible flue liner

Flexible flue liners should be installed in continuous lengths without joiners. Schiedel Rite-Vent can supply all flue liners in specific lengths on drums or in pack form upon request. On TecnoFlex installations, joiners are only permitted where the chimney liner length exceeds the maximum drum length available and details of the installation are agreed in advance, in writing, in compliance with product warranty conditions.

Connection to the appliance or flue box

The connection to the appliance should be made using fire cement/rope or high temperature sealant to ensure a positive seal. Where TecnoFlex is to be fitted to the top of an open fire place, a Schiedel Rite-Vent gather unit should be fitted into the throat of the chimney connected to the TecnoFlex and sealed off. When connecting to a Schiedel Rite-Vent flue box, the flexible liner simply pushes directly on to the fast fix spigot. No sealant is required. When making a connection to a fluepipe in another product type, such as rigid stainless steel single or double wall or vitreous enamel, then the appropriate connector to/from flexible should be used. The connector should be suitably sealed to the appliance spigot ensuring a gas tight joint.

After Installation

Testing before use

This is done by means of a flue flow test as described in BS15287 Parts 1 & 2 (open appliances & room sealed appliances). This can be summarised as follows:- After a visual and physical check of the joints in the system, and ensuring an adequate air supply for combustion has been provided, close all doors and windows in the room in which the appliance is to be installed. It will be necessary to introduce heat to the flue system for a minimum of 10 mins and possibly up to 30 mins using a blow torch or similar. Position a smoke pellet (providing a performance of 5m3 of smoke in 30 secs burn time) at the intended position of the appliance. The test is satisfactory if there is no significant spillage from the appliance position, no seepage over the length of the system, and discharge only from the terminal. If these conditions are not met, the test has failed and all faults must be rectified before connection of the appliance to the fuel supply.

Life expectancy and warranties

Under normal operating conditions and providing the system is installed correctly, it should last the lifetime of the appliance, which normally is 10 years. Flex carries a 10 year conditional warranty. The conditions are that the system is:-

  • Correctly sized and installed in accordance with the manufacturer's instructions, current Building Regulations and relevant British and European standards.
  • Maintained correctly by a qualified and competent person and maintenance records kept updated for both appliance and chimney/chimney liner.
  • Used in combination with an appliance burning only approved fuels in accordance with Schiedel Chimney.

Systems and the appliance manufacturer's instructions

Use after a chimney fire

Whilst TecnoFlex is designed and tested to withstand chimney fire conditions the flue liner could be damaged under the conditions of a chimney fire, and must always be inspected by a suitably qualified individual (e.g. NACS/NACLE member) and replaced as necessary, before using the appliance or fire again.

End User Maintenance

1. Maintenance
Each chimney must be designed to allow for easy inspection; sweeping should be carried out by competent persons. A list of HETAS registered sweeps can be found at www.hetas.co.uk

Chimney flue cleaning and inspection require the use of appropriate tooling - under no circumstances should chemical cleaners or mild steel tools be used to clean or sweep stainless steel chimneys. Mechanical sweeping methods, such as Rodtech, which have been tested and approved by Schiedel Chimney Systems may be used. Cleaning/inspection of any chimney system should be carried out at least once a year, along with maintenance of the appliance, but it is recommended that chimneys serving solid fuel appliances be swept at least twice a year.

2. Warning
Failure to maintain a clean chimney can result in the emission of toxic gases into the dwelling or damage from potential chimney fires. If a chimney fires does occur, professional advice should be sought regarding the condition of the chimney. The chimney should be inspected at least once a year to see if the construction materials are in good condition. Particular attention should be paid to terminals, sections externally exposed above the roof line and inspection openings. Should any component show any sign of deterioration, professional advice should be sought. It could be necessary to replace these components in order to ensure that the chimney can operate correctly.

3. Fuels
It is advisable that only approved fuel recommended in the HETAS Guide or by the appliance manufacturer be used. Household refuse must not be burnt. Wood-burning produces considerable deposits of soot, tarry matter and wood ash. The amount of these deposits can be reduced by burning well seasoned, air-dried (preferably 12 24 months) wood, and by ensuring that an active bright fire is maintained.

4. Appliance Operation
If the appliance is slumbered overnight or for longer periods then it is advisable to run the appliance at controlled high fire condition for a period of at least 15 minutes. Prolonged slumbering of the appliance is a contributing factor to a liner failure. It is important to maintain sufficiently high flue gas temperatures in order to avoid condensate and acid corrosion problems.

5. Ventilation
It is very important that sufficient air for combustion and ventilation is provided to the room containing the appliance to enable correct and efficient working of the appliance and chimney. Recommendations are given in Doc J of the Building Regs, BS EN15287 Parts 1 & 2, Regulations or CIBSE Guidance notes.

6. Downdraughts
There are many possible causes of down-draught problems including the height of the chimney. If these problems occur it is recommended that professional advice is sought. A range of anti-downdraught terminals are available.

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