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flue flexible liners coming out of chimney


What is a flue?

Most houses have for centuries been built with a chimney, and the flue is the void created by the space within its construction. We now tend to use metal pipes or liners known as flue pipes to line or build a chimney, and/or tubes made from Pumice to create a flue with the brand name Isokern.

A flue is a wonderful thing and it allows any hot gasses or smoke from a fire to rise up the flue and out of the top of the chimney. These flue gasses naturally draw or are drawn up the flue because not only does hot air rise, but also because of a difference in temperature and atmospheric pressure between the inside of your house and the outside. You will notice this in winter when it is a beautifully cold crisp evening, when the sky is clear, and the stars are shining. Your stove will burn at is brightest and best, just when you need it. As stove fitters we measure this draw or flue draught in ‘Pascals’ to ensure you have enough natural draw to extract the combustion gasses from your stove and make it burn bright and clear.

What types of Flue pipe are there?

There are four main types of flue pipe;

  • Stainless steel flexible liner
  • Twin Wall factory made insulated rigid liners
  • Pre-formed pumice blocks that assemble to make a chimney and flue combined.
  • Single wall rigid flue that is used in only short lengths, normally straight out of the stove.

Stainless steel flexible liner or flex liner is made in two grades of either 316 stainless steel, suitable for wood only burning stoves and 904 stainless steel suitable for multi–fuel stoves that will burn coal products and wood. We would always recommend using a 904-flex liner for any stove as it will last longer with a longer warranty. We would also recommend that both strips of steel used in the liner construction are made of 904. Some inferior liners save on cost by using 904 and 316. These liners come in different diameters and we mainly use 125 mm and 155 mm, also known as 5 inch or 6-inch liner.

Twin Wall flue pipe is made by having an inner and outer stainless-steel pipe that is packed with insulation. These flue pipes can then be used in a house that does not have an existing chimney. The pipe is insulated to avoid condensation running back into the wood burning stove, and for fire protection in the house. Good quality flue pipe will be closer to any materials that are combustible like timber floor joists. The best quality flue pipes will have a distance to combustibles of 50 mm, and whilst it may not seem like much of a difference the poorer quality is 90 mm and above. In terms of fire protection this additional 40 mm can make all the difference.

Pre-formed Pumice liner is made in sections with a double wall to be filled with insulation, the main brand we use is Isokern and our HETAS fitters are factory trained to fit the product. We can design and build a new chimney to the correct standard and current building regulations in new build houses or for retrospectively adding a masonry fireplace or chamber in an existing property.

Single wall rigid flue (often known as vitreous) is exactly what it says.  Made from a single flat piece of 1mm steel rolled into a tube shape. This is traditionally coated with black vitreous enamel.  Single wall flue pipe is now also available in a matt black finish or stainless steel.

Why use flue liner?

We line chimneys with flexible flue liners to avoid any doubt that the existing chimney can carry away all the by-products of combustion and avoid the possibility of Carbon Monoxide entering your home. Modern wood burners and multi-fuel stoves work more efficiently with a flue liner and help the stove to comply with Eco Design 2022 legislation. This means the stove will burn cleanly, use less firewood and be better for the environment. Twin wall flues are a fire safety device and need to insulate against hot gasses condensating in the flue. They are a cost effective and convenient way to install a log burning stove. They protect your home and enable the stove to work efficiently at high temperatures.

Protect your greatest assets

The two most valuable assets we have tend to be our family and our home and most of the time we will do anything to protect them. So, it’s not worth skimping on cheap liner that will degrade quickly with the risks involved. We use only high-quality liner using specific grades and thicknesses of stainless steel that come from accredited manufactures in the UK. We install these to the guidelines laid out by Building regulations and the manufactures’ guidelines. Our stove fitters are HETAS registered and up to date with their professional training.

As part of our service we will perform a free survey and recommend the best liner for your home. Fire protection and your safety is always at the forefront of our minds when designing and specifying a new stove and chimney system.

Chimney Sweeping

We can’t talk about flues and chimneys without mentioning the importance of chimney sweeping. Regular chimney sweeping is vital to maintain the efficient working of your stove. It must be done at least once a year and in certain situations twice or more. Be sure to use a sweep who is a member of one of the main trade bodies and check that they will give you a sweeping certificate once completed.

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