Fireplaces, chimneys and flues

6.8.16Oil – 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 4543 : Part 1 to Part 3 and BS EN 1859 and installed in accordance with BS 7566 : Part 2, 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 715 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 fluepipe

Factory-made chimney complying
with BS 715:1993
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 fluepipe 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Factory-made chimney complying with: BS 4543-1 (withdrawn April 2000 partially superseded by
■ BS 4543-2
■ BS 4543-3
Refer 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).