1. Each building, where heating boiler is installed, shall have effective system for release of smoke and ventilation
  2. Effect of draft in smoke and ventilating ducts arises as a result of pressure and temperature difference: cooler air from outside and warmer, lighter air from inside of the building
  3. Modern flue systems shall be characteristic with:
    • stability against impact of condensate,
    • stability against eventual burning of soot,
    • density that ensures proper draft and safety for user.
  4. The minimal inner diameter of the flue shall not be less than 140 mm (with exception of boilers of condensation type with closed combustion chamber).
  5. It is recommended to use flues with circular cross section, because they have lower frictional resistance when passing through smoke duct. Advantage of such cross sections of smoke ducts is also greater efficiency during periodical cleaning of them.
  6. Cross section of the flue shall be adapted to its height, capacity and type of the heating boiler, as well as to type of used fuel.
  7. Flue outlets shall be accessible for cleaning and periodical control. Therefore free access to flues shall be ensured on roof.
  8. It shall be ensured that cleaning door is situated in place suitable for cleaning of flue and distance from the door to nearby situated combustible materials is at least 30 cm. If it is necessary to construct additional cleaning door over the connection T-piece (e.g., in the loft), floor made of combustible materials shall be covered with fireproof material (e.g., metallic sheet, stone or ceramic tiles). In case, when above roof section of flue is considerable or roof has high slope, very practical solution is to install an additional cleaning manhole about 100 cm above the roof.


Installation of an additional cleaning manhole shall be coordinated with chimney sweep.