Ventilation System Comparison: Choose with Confidence

Why is a good ventilation system important?

A healthy indoor climate starts with sufficient fresh air. In well-insulated homes, as increasingly common in Flanders, natural ventilation through cracks and gaps is insufficient. Without controlled air exchange, moisture, CO₂ and harmful substances accumulate. This leads to mold, allergies and a stuffy home. A well-designed ventilation system solves this and also saves energy.

The four ventilation systems at a glance

The basic classification looks at how air is supplied and exhausted: natural (through grilles and windows) or mechanical (with fans). This creates systems A, B, C and D. Below we explain each system clearly so you can easily compare them.

System A: natural supply and natural exhaust

This is the simplest form. Air enters through window grilles and open windows; exhaust happens through vertical ducts or vents. The system reacts to wind and temperature differences. In modern, airtight homes it is often insufficient. System A is mainly found in older houses without major renovation. It requires active ventilation by the resident.

System B: mechanical supply and natural exhaust

A fan blows fresh, possibly filtered air into the home. The air escapes through natural openings. This system is rarely used in residential buildings because of the higher risk of drafts and pressure differences. It is sometimes applied in commercial buildings.

System C: natural supply and mechanical exhaust

System C is the most common system in Flanders, especially in renovations. Fresh air enters via self-regulating grilles in windows or façades. A central ventilation unit mechanically extracts the polluted air in the kitchen, bathroom and toilet. The advantages: simple installation, low cost and energy-efficient because the exhaust can be demand-controlled. Disadvantage: no heat recovery, so in winter cold air enters directly.

System D: mechanical supply and mechanical exhaust (balanced ventilation)

System D, also called balanced ventilation, controls both supply and exhaust mechanically. A heat exchanger in the ventilation unit transfers the heat from the exhausted air to the incoming fresh air. In this way, up to 90% of the heat is not lost. This system is ideal for new builds and major renovations where an airtight building envelope is present. It requires a network of air ducts and a higher investment, but pays for itself through energy savings. Moreover, it filters the incoming air, which is good for allergy sufferers.

Direct comparison: system C versus system D

The choice between system C and D is often the central question. We list the key differences:

• Ease of installation: System C only requires a exhaust duct and grilles; system D needs a full duct network.
• Energy consumption: System D uses slightly more electricity due to the dual fans, but saves significantly on heating costs thanks to heat recovery.
• Noise level: Modern C units are quiet; D units are best placed in a technical room to minimize noise.
• Maintenance: Both systems require filter replacement and cleaning of the ducts. For D, there are two filters and a heat exchanger that must be checked annually.
• Cost: A system C is cheaper to purchase and install than a system D. Expect to pay €2,000 to €4,000 for C, and €5,000 to €10,000 for D, depending on the size and complexity of the house.

Which system suits your home?

The right choice depends on your specific situation:

• Old house, partially insulated: System C is often the best option. It significantly improves air quality without major works.
• New build or passive house: Choose system D. The airtightness requires balanced ventilation with heat recovery.
• Major renovation with insulation upgrade: Here you can consider both C and D. D is future-proof, but C can also suffice if you prefer fewer ducts.

Grants and regulations in Flanders

The Flemish government encourages good ventilation. For system D with high efficiency, you may be eligible for a grant through Mijn VerbouwPremie under certain conditions. Also in total renovation, ventilation can be part of the EPB story. Ask your local expert about the current support measures.

Choose a ventilation system yourself? Don't do it alone

Every home in Flanders is different. A ventilation advisor looks at the building physics, the habits of the residents and the budget. This way you avoid wrong choices, such as a system D in a non-airtight home or grilles that cause drafts. At ventilatiesysteem.info you first come by for a free assessment: our local specialists measure your situation and give independent advice. So you choose with confidence the system your home really needs.