Ventilation is not optional comfort: it is the compulsory counterpart of a well-insulated house. The more airtight you make your home — insulation, new windows — the more moisture and pollutants build up. In Wallonia, heat-recovery ventilation is grant-aided on a base of €680 per installation, multiplied by the income coefficient. In Flanders, a grant exists for central ventilation (demand-controlled system C and system D with heat recovery).
Why it has become essential
An old, uninsulated house "breathes" through its defects: joints, leaky windows, chimneys. That unintended air renewal is expensive in heating terms, but it does remove the moisture occupants produce — showers, cooking, laundry, breathing.
As soon as you insulate and replace the windows, those leaks disappear. Without a ventilation system the outcome is predictable: condensation on the glazing, mould in cold corners, stale air, and in time damage to the building fabric. It is the classic half-finished renovation scenario.
System C or system D
System C — mechanical extract
Fresh air enters through vents in dry rooms (living room, bedrooms) and is mechanically extracted from wet rooms (bathroom, kitchen, WC). Simple, inexpensive, easy to retrofit. Its limitation: incoming air is at outdoor temperature, so in winter it has to be heated. Demand-controlled versions, driven by humidity or CO2 sensors, cut that loss significantly.
System D — balanced ventilation with heat recovery
Two duct networks: one brings in fresh air, the other extracts stale air. The two streams cross in a heat exchanger where the outgoing air warms the incoming air without mixing. Recovery efficiency is high and incoming air is filtered — a real plus in the city or for allergy sufferers.
The trade-offs are real: markedly higher installation cost, a duct network to route (awkward in heavy renovation), and compulsory regular maintenance — filters to replace, ducts to clean. A poorly maintained system D loses its benefit and can even degrade air quality.
Grants by region
In Wallonia, heat-recovery ventilation has a base amount of €680 per installation, multiplied by your income category coefficient (× 6 in R1, × 4 in R2, × 3 in R3, × 2 in R4), within the limit of 70% of the invoice including VAT in R1-R2 and 50% in R3-R4. The prior home energy audit is mandatory, and the whole file must be submitted before 30 September 2026.
In Flanders, Mijn VerbouwPremie covers the installation of a central ventilation system — demand-controlled system C, system D with heat recovery, or partial systems. Since 1 March 2026, access to renovation grants is restricted to income categories 3 and 4 for everything that is not a heat pump or heat pump water heater: check your category before counting on it.
In Brussels, Renolution grants have been suspended since 1 January 2025. What remains: 6% VAT for a home older than ten years, municipal grants and the ECORENO credit.
⚠️ The order of works matters. The duct network for a system D is far easier to install while ceilings are open. If you are planning a heavy renovation, ventilation is decided at design stage, not after the finishes go in. Added last, it costs more and shows more.