Stoves and Chimneys

Stoves  and most gas Fireplaces are only useable with a suitable Chimney. Chimneys come in many various types Here at Boston Heating we endeavour to help get your fireplace or stove project to completion using some of the best products and our own specialist stove installers and fireplace fitters

The European Standard BS EN 1443: 2003 Chimneys – General Requirements, categorises chimneys and flues into three basic designations:

Custom Built Chimneys - Constructed on site using factory made flue liners.

System Chimneys - Prefabricated chimney systems. Manufactured in a factory and assembled on site. The key benefits of chimney systems lie in their off-site production and preformed insulation.

Connecting Flue Pipes - Pipe specifically designed to connect an appliance to the flue or chimney.

Chimneys and flues are also available in a number of different materials – stainless steel, concrete, pumice, clay or ceramic and plastic. Concrete, pumice and clay or ceramic are collectively referred to as masonry chimneys. Plastic flues are only allowed to be used with low temperature condensing applications.

Care must be taken to check the designation of stainless steel chimney systems and flexible liners as a limited number are specifically designed for use with gas fired appliances. These must not be used with wood burning or multi fuel appliances. Clay and pumice chimney systems and liners are suitable for wood, multi fuel, oil and gas. Concrete gas flue blocks as the name suggests are only to be used with gas effect fires and must not be used with wood or solid fuel fires.

Factory produced pumice and ceramic chimney systems are also available. Although they can be retrofitted, pumice and ceramic chimney systems tend to be used in new houses, because they require a foundation and their construction method is best suited to the skill set of a bricklayer.


Here at Boston Heating we can help you in finding the right solution for your property.


THe most popular way of lining a chimney that already exists is by flexible flue liner 

Stainless steel flexible liners are certified to BS EN1856-2. Flexible liners are used to reline an existing chimney. Care must be taken when selecting a flexible liner.

There are two types of flexible liners:

  • Single skin liners for use with gas appliances and
  • Twin skin liners, manufactured from overlapping strips of high grade stainless steel to give a smooth sealed flue-way. 
  • These liners should be used with wood and multi-fuel appliances.

Single skin liners must never be used with wood or multi-fuel applications.There are two types of twin skin liner 

We supply  the 316 liner and 904 liner  both suitable for wood or multifuel stoves.

One of the keys to a well performing chimney is consistent insulation along the complete length of the flue. Clay/ceramic, concrete and pumice liners require insulation to be prepared and added on site. Stainless steel and ceramic system chimneys are supplied with effective insulation. Double wall pumice chimney systems have an air gap between the walls of the inner and outer block. The air gap combined with the natural insulating properties of pumice provide effective insulation along the length of the chimney.

SAP is the Standard Assessment Procedure used to calculate the overall energy efficiency and carbon output of a house.

The ideal location for a chimney is on the inside of the building. That way it can benefit from being kept warm. Chimneys situated outside the building can be affected by cold weather causing poor up draught and condensation, particularly if they are un-insulated. It is therefore important that a cavity wall is continued around a lined masonry chimney or a factory made insulated chimney system is used for external applications.

It is important to match the internal diameter of the flue with the outlet on the appliance. It should never be less than the outlet diameter of the appliance. The appliance manufacturer’s chimney sizing recommendations should always be followed. For free-standing stoves, boilers and cookers up to a maximum of 20KW, that are not in a fireplace recess, the minimum flue size is 125mm round or square if the appliance has passed the DEFRA requirements for smokless zones and 150mm if this is not the case.

Before commencing on a new build project if you are having a stove It is well worth talking to us to discuss your chimney 

Both the Regulations and the Standards recommend that bends in the chimney be avoided, as a straight vertical chimney performs better. If bends are necessary there must be no more than four in the length of the chimney. The angle of the bend should be no greater than 45° from the vertical, with the exception that 90° factory made bends or tees may be treated as being equal to two 45° bends. Where System Chimneys are used, always use the standard offset components which are available from the chimney manufacturer. For stainless steel chimneys, certified to BS EN 1856, the distance between bends must be no greater than 20% of the total chimney length. It is recommended that a vertical rise of 600mm should be allowed immediately above the appliance before any change of direction. An inspection hatch is required between each offset.

For open fires with a standard fire opening up to 500mm wide by 550mm high the minimum required flue diameter is 200mm round or 175mm square. For larger open fires, such as inglenooks, dog grate installations or special appliances and stoves designed to operate with a fire opening greater than 500mm x 550mm, the flue size should be at least 15% of the free unobstructed area of the fire opening (including sides if open). Many Decorative Fuel Effect gas fires (DFE's) that imitate a coal or log burning open fire require the same chimney arrangement as for solid fuel open fires and must be installed in accordance with British Standard BS5871:Part 3:2005

It is worth noting that in SAP the assumed standing air loss for a flue with an internal diameter of 200mm and above is 40 cubic meters per hour. With a flue diameter of less than 200mm or a chimney system that incorporates a damper the ventilation rate is halved to 20 cubic meters per hour. (The damper must only be closed when the appliance is not in use). This can have a significant impact on the energy rating of a house.

SAP is the Standard Assessment Procedure used to calculate the overall energy efficiency and carbon output of a house.





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Boston Heating

Address: Church Road, Boston PE21 0LG
Telephone: 01205 310 327