Flexible Chimney Liner

Class 1 - Wood And Coal Burning - Flexible chimney liner  Class 1 chimney liners (Also known as T450) are used for wood and cowl burning stoves, open fireplaces and gas or oil appliances generally where the flue gas temperature is likely to exceed 250ºC. This type of liner has a smooth inner as well as the convoluted outer therefore giving a smooth flow for gases and easier chimney cleaning. Diameters: 125mm (5inch), 150mm (6inch), 180mm (7inch), 200mm (8inch), 225mm (9 inch), 250mm (10inch), 300mm (12inch), 350mm (14inch)

Class 2 - Gas And Oil Burning - Flexible chimney liner  Class 2 flexible chimney liners (Also known as T250) should only be used where the appliance manufacturer has stated that this type of chimney liner is suitable, this is usually where the flue gas temperature is unlikely to exceed 250ºC. Diameters: 100mm (4 inch), 125mm (5inch), 150mm (6inch), 180mm (7inch), 200mm (8inch)

The information below should answer some questions regarding chimney lining and has been compiled by the proprietor of Hotline Chimneys who has almost 10 years installation experience. If you need further information don't hesitate to contact us at the link above.

Flexible chimney liner construction and usage

Only relevant to class 1 chimney liners: 

Although described by some as twin wall chimney liner (we tend to describe it as twin skin chimney liner, as not to confuse it with insulated flue systems), there isn't any insulation or space between the two skins. In the chimneys liners manufacture an inside and outside skin are created, the inner being of smooth construction to aid flow hot gasses and sweeping, the outside is convoluted to maximize protection during installation of the flue lining.

Flexible chimney liner for use with wood and coal (class 1), needs to be installed the right way round. A good way to describe the inside of a flexible flue liner is as being like weather boarding on a building, each of the boards (often referred to as featheredge) working in a similar way. The purpose of the lap on the inside of the is to ensure soot/tar/creosote within the chimney liner can easily move back down without being disrupted.

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\   / Flexible flue liners are lapped like this on the inside.

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Relevant to both class 1 and class 2 chimney liners:

Flexible chimney lining is only for use within masonary chimneys, from a building regulations point of view flue liner should only be installed within 100mm (4") of masonary. It is acceptable to rebuild the chimney stack and then line the whole flue, or to carry out repairs to a chimney and then line it. It isn't acceptable to use flexible liner in a new chimney or where the majority of the chimney flue has been rebuilt.

Fitting of flexible flue liner tips

When measuring a chimney with bends for flue lining, the most accurate method we have found is to use chimney/drain rods, as these will lay in a flue in a very similar way to the flexible liner. Other methods such as measuring the room heights or dropping a piece of string or a tape measure through the chimney flue could never mimic the exact way a flexible flue liner will lay.

Chimneys must be swept clean before installation of a flexible flue liner, this not only prolongs the life of the flue liner as it won't be in contact with lots of corrosive deposits within the flue, but also makes the whole experience a lot cleaner and less dangerous. There is a strong likelihood of dislodging either large chunks of soot or even big bits of masonary when lining a chimney.

Chimney lining in the UK can be carried out by a competent person as a DIY project but the installation must be checked by a building control officer from your local council. The flexible flue lining will be checked after the installation is complete and a certificate issued to confirm the flexible flue liner has been installed correctly. There will be a fee to pay, these vary depending on your area but are reasonable. Two more important points worth mentioning. 1, If  you sell your home the buyers surveyor will probably request the above information, if it isn't forthcoming it could hold up the sale. 2, If there were ever a fire or accident caused by or involving the flexible liner, it is possible the insurers could hold up or even void any claim if it hadn't been inspected by building control. 

Although a nose cone is helpful for all installations of a flexible liner, on some of the more awkward jobs (such as where there is more than one bend, or the original flue size is close to that of the liner) we advise you do the following: Put the nose cone on to the end of the flue liner as usual (there's no need to tape of screw it at this stage), next find a piece of webbing about 2ft long and a couple of inches wide (we would always use the handle off a one ton sand bag - a customer suggested once he had used an old seat belt, which is also ideal). Hang each end of the piece of webbing over either side of the end of the chimney liner, so as to create a loop at the top, then tape the webbing to the liner (all the way round) with a stretchy tape such as insulation tape, also taping over the nose cone a bit at the same time to keep it still. Now a length of strong cord or rope can be tied to this loop to assist getting the flue liner through the chimney, although there will obviously be a limit to how hard you will be ale to pull so as not to break the chimney liner, the idea is that the tape will stretch if the chimney liner catches on the side of the flue or a bend, where as if you were to rely on the nose cone either taped or screwed to the liner alone, there is a lot more chance that it may come off or even break the end of the flexible liner.

When installing a flexible chimney liner all joints on fittings such as flue adaptors should always be made with the female coupler facing upwards, and any male fitting fitted in to the female component from above. This is to ensure condensation remains within the chimney liner and to aid sweeping as mentioned above.

All of the manufacturers tend to advise/assume a flue liner will always be installed from the top, where as in fact they can often be pulled up from the bottom, especially where fireplaces such as inglenooks are concerned. At the end of the day, assuming you are taking our advice and two people are installing the chimney liner, it will often be worth trying to install from the bottom, even if you may have to give up and install from the top anyway, just don't pull too hard. If the chimney has a bend it can often be easier to leave the liner on the roll at the bottom, only feeding the flue liner off the roll as it goes in to the chimney. Installing the chimney liner in this way allows the person at the bottom to turn the whole roll slightly when the end reaches the bend, the natural bend in the flexible liner then tends to help it go around the corner a lot easier than it might otherwise.

Please check back again as we will add more information as and when time allows.