Fahrenheit

For a fire to work successfully, it must be connected to a sound chimney and correctly sized flue. The functions of a chimney are to safely remove the products of combustion from the fireplace or appliance to outside without causing danger to the occupants of the house or setting the house itself on fire. A chimney works because hot air rises and always moves from high to low pressure. Factors such as running the appliance at a very low output or cold air leaking into the flue, will cool the gasses and affect the performance of the chimney.

In houses built since the introduction of the 1965 Building Regulations, all flues must be built with liners during their construction. This is usually done with clay liners, which should last the life of the building. However, in houses built prior to 1965, lining was less common. Flues were usually “parged” (rendered) on the inside with lime mortar. This parging suffers attack from acids and tars produced during combustion, and gradually deteriorates. The flue is then in poor condition, often leaking fumes or tars into the walls or other parts of the building. Sadly, many houses built since 1965 suffer similar problems due to badly installed flue liners and need further attention.

What is a flue liner?

There are many flue liners available. Years ago the only way of re-lining a flue was to open the chimney up the full length of the house and install round or square clay, sectional liners into the flue. Then the brick/stone work would be replaced and the interior/exterior made good.

Nowadays there are much easier and cheaper ways to re-line a flue. The most common way when installing a stove is to fit a Stainless Steel Flexible Liner. These come in rolls of varying lenths. They are fed down the chimney from the roof throughout the full length of the flue. Once installed you have a completely impervious lining within your flue solving all of the problems below.

Below: Flue leaking tar and water

due to flue being unlined

Why Install a liner?

There are a number of reasons why we re-line a chimney:

  1. The flue is leaking smoke and fumes into
  other rooms or parts of the building.

  2. To stop condensates or tar seeping
  through the chimney walls causing
  staining, either inside or outside the
  building (a common problem with wood
  burning stoves due to lower volumes of
  hot air moving throughout the chimney in
  comparison with an open fire).

  3. To reduce the size of the flue if it is too
  large for the type of fire or appliance being
  used. Reducing the size of the flue
  speeds up the flow of gases which
  reduces tar and soot build up.

  4. The flue is too cold, particularly if on an
  outside wall, and is not drawing properly.

  5. If the chimney was built since 1965, but with the liners fitted the wrong way up, tar and condensate
  leakage may occur. This is very common.

  6. The old flue surface is eroded and rough, causing frictional resistance to the flow of the gasses
  resulting in poor updraught.

  7. The chimney is not sweepable due to acess to the flue being too small.

  8. The chimney has not been finished in a suitable fashion for a stove to be connected in a watertight
  and airtight manor.

Re-lining of a chimney solves all of the above issues making your stove perform the best it possibly can. Not to mention keeping your family and property safe and making sweeping a very clean and simple operation.