Construction products detail

Cross-sectional reductions for chimneys

Cross-sectional reductions for existing chimneys are used for renovation and/or modernisation. The purpose may be to upgrade the chimney for operation under wet conditions or adapt the cross section of the chimney to a newly connected heating appliance, e.g. a low-temperature boiler. A cross-sectional reduction can affect the flue gas velocity. Application-specific calculations for correct flue sizing therefore form the basis for cross-sectional reductions.

Regulatory framework

In this work area, DIBt grants:

  • national technical approvals (abZ) for flue liners and/or sections of flue liners for cross-sectional reduction that are not covered by the applicable harmonised standards or a European Technical Assessment;
  • general construction technique permits (aBG) for the execution of cross-sectional reductions not covered by the execution standard DIN 18160-1.

National technical approvals and general construction technique permits can be granted together in a single decision ('combined decision').

European Technical Assessments (ETAs) can also be issued for construction products for cross-sectional reductions which are not (fully) covered by a harmonised technical standard. For construction products covered by an ETA, a general construction technique permit for the application may be pertinent.

The technical rules to be observed in the execution of cross-sectional reductions include:

  • DIN EN 13384-1 – Chimneys – Thermal and fluid dynamic calculation methods – Part 1: Chimneys serving one heating combustion
  • DIN EN 13384-2 – Chimneys – Thermal and fluid dynamic calculation methods – Part 2: Chimneys serving more than one heating appliance
  • DIN V 18160-1 – Chimneys – Part 1: Design and performance

Please also note the relevant provisions of the federal states following MVV TB, Annex 8, Section 8.3 (2017/1) or Annex 14 (2019/1 and following).

pdf-Datei Muster-Feuerungsverordnung (MFeuV) Stand: September 2007, geändert durch Beschluss der Fachkommission Bauaufsicht vom 28.01.2016 und 27.09.2017; Fachkommission Bauaufsicht der Bauministerkonferenz

National procedure

A national technical approval (abZ) and/or oder general construction technique permit (aBG) is granted upon application (see Model Building Code (MBO), Sections 16a(2) and18(2) and (4)). This also applies to amendments and supplements to, or renewals of existing approvals and/or construction technique permits.

No formal requirements apply. The following information is needed: name and address of the applicant, description of the product and/or construction technique and its field of use or application, type of decision required (new decision, amendment or supplement to, or renewal of, an existing decision).

Please feel free to use the template below.

European Technical Assessment (ETA)

To start the ETA procedure, please submit the form below. We will then check if the prerequisites for issuing an ETA are met, i.e., in particular, if the product is not fully covered by an existing harmonised standard. If the prerequisites are met, we will check whether a European Assessment Document (EAD) covering the requested assessment scope already exists or still needs to be developed. If an EAD needs to be developed or amended, a complete technical file needs to be established before the procedure can begin.