Ventilation — invisible comfort, measurable energy savings

Why you can no longer do without mechanical ventilation in 2026

Modern homes are hermetically sealed — insulated glazing, tight joints, mineral wool in the cavity. Excellent for the energy bill but disastrous for air quality. Without mechanical ventilation, moisture accumulates (leading to condensation and mould), CO2 (poor sleep, lost concentration) and volatile compounds from paint, furniture and household chemicals.

Standard EN 12831 and the Flemish EPB regulations prescribe a concrete flow rate: minimum 3.6 m³ per hour per m² of habitable floor area. For a 150 m² terraced house that's 540 m³ per hour of fresh air — physically unachievable in a well-insulated home through natural infiltration without a mechanical system.

The three main benefits

• Healthier indoor air: European studies show that poorly ventilated homes have indoor air quality 2-5× worse than outdoor air. Chronic exposure leads to fatigue, allergies, and long-term respiratory disease.
• Moisture and mould control: every occupant produces 2-4 litres of moisture per day (breathing, showers, cooking, plants). Without mechanical extraction this condenses in cold corners and causes mould — with potentially costly remediation.
• Energy savings via heat recovery: system D with heat exchanger reuses 85-92% of the heat from extract air. In a typical 150 m² home this means €400-€700 per year saved on heating. Against an install of €4,500-€9,000, a payback of 7-15 years.

Ventilation and heat pump — the inseparable duo

A heat pump runs on low water temperatures (35-45 °C), made possible by good insulation AND controllable ventilation. A home with uncontrolled ventilation constantly lets large quantities of cold fresh air in (via gaps, windows), forcing the heat pump to work harder — the COP drops and your bill rises. In short: system D + heat pump = 2-4× more efficient than heat pump alone in a leaky home. This is why we almost always include ventilation in a full renovation.

Ventilation legal framework — what is required?

New-build

Since 2006 mechanical ventilation (system C or D) is required for every new-build in Flanders, Brussels and Wallonia. The EPB regulations prescribe minimum flow rates per room type (kitchen, bathroom, WC, bedroom). An EPB reporter verifies this before handover.

Renovation — "major energy renovation"

If your renovation updates at least 75% of the building envelope (windows + walls + roof), mechanical ventilation is required. In practice: every EPC renovation from label E/F to C requires system C or D.

EPC renovation obligation Flanders

Homes purchased after 01/01/2023 with label E or F must be renovated to label C within 5 years. Ventilation alone usually does not produce a label jump (+0) but is required in the package. The smartest combination: heat pump + roof insulation + ventilation typically produces a jump from E to C.

Brussels: Prime Renolution

Subsidy for system C or D in a renovation: up to €1,800 depending on income category and system type. System D is more highly subsidised because of heat recovery.

BTW

6% VAT for homes older than 10 years (through 2029). Since 01/01/2026 also 6% for new-builds for 5 years.

Installation process — what to expect

System D in a new-build

Typically 5-7 days of execution, included in the shell phase. Ducts (Ø125-160 mm) are embedded in the floor slab (shell) or in a false ceiling run. Central unit (80×80×40 cm) in a utility or technical room. Heat exchanger with automatic bypass (summer mode). Filters must be cleaned every 6 months, replaced every 2 years (€40-€80 per set).

System D in renovation

More complex than new-build. Ducts must be routed through false ceilings, cupboards or shaft voids. Install time typically 1-2 weeks for a 150 m² terraced house. We produce an upfront 3D plan so you know exactly which ducts run through which room at what height. In some cases we pick a decentralised system D (separate heat exchangers per room) to avoid ducts — more expensive but less impact on finishes.

System C in renovation

Cheaper renovation choice. Mechanical extract fan (roof or attic), 100-125 mm ducts to kitchen/bathroom/WC, window grilles in bedrooms and living room for supply. 2-5 days of execution. Demand-controlled regulation (CO2 or humidity) further reduces energy use. No heat recovery but also no heavy infrastructure.

Commissioning

Flow-rate measurement per room per EPB standard. Calibration of the modulating fans. Resident walkthrough on filter replacement and maintenance. Official report with measured flow rates for your EPB file.

Maintenance — what you do and what we do

Yourself (every 6 months)

• Clean or replace filters (G4 pre-filter: vacuum-clean, F7 fine filter: replace)
• Vacuum grilles and vents
• Check the status LED on the unit

Us (every 1-2 years)

• Duct cleaning (endoscopic camera + vacuum) — strongly recommended every 5-7 years
• Clean the heat exchanger (dismount bypass, flush)
• Check fan bearings, measure motor current
• Re-calibrate flow rates if needed
• Moisture measurement in ducts (condensation risk?)

Maintenance contract: €180-€280 per year depending on system and scale. If you have a maintenance contract on your heating installation, we combine both visits.

Ventilation FAQs