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Air

Ventilation system A, B, C or D: what's the difference?

Short answer

A is fully natural, B mechanical supply, C mechanical extract, D mechanical supply and extract (often with heat recovery). In Flanders new builds must have one of these four in full.

Airflow through the home: Floor plan from dry to wet: supply in living rooms and bedrooms, extraction in kitchen, bathroom and toilet, with flow rates.
Airflow through the home — Floor plan from dry to wet: supply in living rooms and bedrooms, extraction in kitchen, bathroom and toilet, with flow rates. (The text inside the figure is in Dutch.)

Explanation

In system A air comes in through grilles and leaves through ducts, without a fan. In C a fan extracts air in wet rooms; fresh air comes in through grilles. In D fans blow air in and out; a heat exchanger (MVHR) can reuse heat from the exhaust air. Maintenance determines how well each system works.

Rules of thumb

  • System D: replace the filters 2 times a year and vacuum them in between. [SW-S31]
  • System D: have a technician visit about every 2 years; clean the ducts about every 8 years. [SW-S31]
  • Systems A and C: keep grilles always open and clean them at least once a year. [SW-S30]

Pitfalls

  • Never switch ventilation off completely, except in an emergency (e.g. fire or smoke outside). [SW-S30]

By region

Flanders
Complete ventilation system mandatory for new builds (EPB). [SW-S50]

Search terms

These search terms are in Dutch; only terms that also find a topic in English are links.

ventilatiesysteem WTW balansventilatie systeem D systeem C

Read also

General information, not personal advice. Check the source and reference date.

Sources

  1. SW-S30 Tips voor beter en energiezuiniger ventileren — Milieu Centraal (Reference date 2026-09-27)
  2. SW-S31 Balansventilatie: onderhoud en gebruik — Milieu Centraal (Reference date 2026-09-27)
  3. SW-S50 Nieuwe EPB-eisen voor 2024 voor nieuwbouw en renovatie — VEKA (Vlaams Energie- en Klimaatagentschap) (Reference date 2026-09-27)

Reference date: 2026-09-27 · Translated with AI from the Dutch original.