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Air-recirculation possible

Clean Air Return An efficient heat recovery requires the complete or partial return of the extracted air into the labour environment after cleaning. A share of the substances (e.g. wood dust) in the extracted air - depending on the dust reduction efficiency - is thereby returned to the labour environment. The observation of the limit values of the wood dust level in the returned air on Filter units resp. Dust extraction units is certificated by means of a type test by test centres (notified bodies), BGIA (Berufsgenossenschaftliches Institut für Arbeitssicherheit) resp. GS (= proofed safty; a public test centre). The following principal for units with clean air return applies actually in Germany:

  • A 50% air return requires a residual dust content (in the returned air) <0,2mg/m³, which corresponds to the use category H2.
  • A 100% return requires even <0,1mg/m³ residual dust content, which corresponds to the use category H3.


Prüfzertifikat Verwendungskategorie H2