6.8 Fireplaces, chimneys and flues

6.8.16 Oil – chimneys

Chimneys shall incorporate flues capable of safely conducting products of combustion from an open fire or other appliance to the external air. The structure shall be capable of supporting the flue lining and shall provide adequate protection to adjacent materials. Issues to be taken into account include:

  1. stability, size and direction
  2. separation from adjacent spaces, materials and combustible materials
  3. flue liners
  4. resistance to frost/chemical attack
  5. resistance to weather.

Stability, size and direction#

Flue pipes should:

  • have a free area which is at least the same size as the outlet of the appliance
  • where possible, be vertical (where this cannot be achieved, there should be no more than two bends, which should not be more than 45° from vertical).

Factory-made insulated chimneys should:

  • be designed in accordance with BS EN 1856 and BS EN 1859 and installed in accordance with BS EN 15287, or be assessed in accordance with Technical Requirement R3
  • have a minimum operating life of 30 years
  • where they are part of a component system, comply with BS EN 1856 and installed in accordance with BS 5440.

Separation from adjacent spaces, materials and combustible materials#

Table 7: Protecting buildings from hot flues for flue gas temperatures not more than 250°C

Flue within:Protection measures
Connecting flue pipe

Factory-made chimney complying with BS EN 1856
Flues should be a minimum of 25mm from any combustible material. This is measured from the outer surface of the flue wall and the inner wall of multi-walled products.
Where flues pass through a combustible wall, floor or roof (other than a compartment wall, floor or roof) separation can be achieved through the use of a non-combustible sleeve around the flue pipe or chimney with a 25mm air space to the relevant flue wall. The air space could be wholly, or partially, filled with non-combustible insulating material
Factory-made chimney complying with BS EN 1856Refer to appropriate British Standards and manufacturers’ recommendations
Masonry chimneyProvide a minimum of 25mm of masonry between flues and any combustible material
Flue block chimneyProvide flue block walls a minimum of 25mm thick
Flue assemblies for roomed-sealed appliances Flues passing through combustible walls should be surrounded by a minimum of 50mm insulating material. Provide a minimum clearance of 50mm from the edge of the flue outlet to any combustible wall cladding

Flue liners#

As for gas flue pipes where the flue gases are unlikely to exceed a temperature of 250°C (see Clause 6.8.10). As for solid fuel flue pipes where the flue gases are likely to exceed a temperature of 250°C or the temperature is not known (see Clause 6.8.5).

Flexible flue liners are not acceptable for new build.

Resistance to frost/chemical attack#

Resistance to frost attack as for solid fuel (see Clause 6.8.6).

Resistance to weather#

Resistance to weather as for solid fuel (see Clause 6.8.6).

Last updated: 2nd January 2024

Back to top ⇧