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CICO chimney protectionwood burning fire with CICOTable with a wood fireSafe fires with CICO

Design Notes

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The design of any flue should take into account all of the following:-

  • Flue temperature
  • Heat resistance
  • Thermal stresses
  • Acid resistance
  • Shape and size of the flue
  • Soot build up
  • Size and type of appliance or open fire it is to serve
  • Insulating properties

All of these items can cause problems if not considered at the initial stage before any works commence.

The CICO in-situ system can be the solution to all of these issues. The system insulates to maintain the flue gas temperature and has been tested to the highest temperatures proving the ability to deal with even soot fires these going to be the cause of the greatest temperature the flue will have to resist. The CICO system does not expand so thermal stress is not an issue, unlike other types of flue. The CICO liner is one continuous smooth liner cast to the size required by appliance, this reduces the soot build up and allows the flue gases to flow easily up the liner that is acid resistant.

The problems with a chimney could be nothing to do with the chimney or building. Nearby hills or adjacent tall buildings or trees can deflect the wind to cause turbulence around the flue terminal, or worse cause it to blow down the flue. This can be recognised by occasional puffs of smoke in to the room. If the flue terminal is on the prevailing wind side of a taller object i.e. the house roof, taller building, tree or nearby hill, it could be in a higher pressure zone. This is more likely to produce a continuous fume emission when the wind is blowing. This will be accentuated if the appliance air supply is on the leeward side of the obstruction.

The terminal or chimney pot is an important component of the flue, as it can take the flue gases away from the turbulence of the stack and out of the high-pressure zone.

Structural Timber clearances
If the chimney passes through a timber structure i.e. a floor, a minimum clearance of 38mm should be maintained between the outer face of the chimney and any structural timber. But floorboards or skirting boards can be in contact with the chimney.

Building Regulations
The requirements for the design and construction of chimneys in England and Wales are given in the approved document - Part J: 2002 Edition - Combustion appliances and fuel storage systems.

In Scotland, the requirements are in Part F of the Building Standards (Scotland).

In Northern Ireland the requirements are in Technical Booklet L, Building Regulations (Northern Ireland) 1990.

The regulations state the basic requirements for appliances and chimneys. These are straightforward and obvious requirements, including adequate air supply, combustion gas safe discharge and fire protection of the building.

The other less obvious requirements in England and Wales are, completion of a checklist detailing the construction of the chimney should be completed and a notice plate to be attached within the building.

The regulations require all systems used are of a recognised standard and state that a cast in-situ flue liner must use independently certified material and installation procedures. In testing the system was considered equivalent to the designation T600 N2 S D3, kept in good working order the lining will have a minimum life of 60 years.

Document J gives minimum flue sizes. It is important to link the flue size to the appliance or open fire for which it is being used. Too small and the appliance or open fire will not draw properly which could lead to carbon monoxide, too large and the flue will be inefficient and lead to excessive soot and tar deposits.

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