Mechanical ventilation (VMC): how it works in French properties

How does a VMC (ventilation mécanique contrôlée) work?

The common type is a VMC simple flux (single flow). A central fan unit, usually in the roof space or a cupboard, pulls stale, damp air out through grilles in the bathroom, WC and kitchen. Fresh air comes in through small vents at the top of the windows or in the walls of the living room and bedrooms.

The fan runs all the time at low speed, with a boost for cooking and showers. Because the air keeps changing, humidity doesn't build up, and humidity is what causes the mould common in older apartments. The fan unit lasts many years, and the grilles and filters need cleaning regularly.

What is the difference between VMC simple flux and VMC double flux?

Simple flux throws the warm air out with the stale air. In winter you're heating air that the fan then expels.

A VMC double flux adds a heat exchanger. Outgoing and incoming air pass each other without mixing, and the warmth moves across to the fresh air coming in. A good unit recovers most of the heat, which lowers heating bills and helps the DPE rating. It costs more, the unit is bigger, and it needs ducts to every room. It pays off in a well-insulated house, where ventilation is a large share of the heat lost.

Which grants still cover a VMC?

Since 1 September 2026, VMC double flux has left MaPrimeRénov' par geste. It's now funded only inside a whole-house rénovation d'ampleur, which is limited to a principal residence. CEE credits (energy-supplier grants) can still apply to a double flux system or to a humidity-controlled simple flux (VMC hygroréglable). For CEE, the installer must hold RGE certification, so ask for the RGE number to be printed on the devis (written quote).

Why a VMC matters in a Riviera second home

Without ventilation, moisture from cooking, showers and breathing has nowhere to go. It condenses on cold walls, windows and corners. Over time that means mould and, in bad cases, damp in the structure. A house shut up for months at a time suffers most, so leave the VMC running while you're away and keep the window vents clear.

A missing or broken VMC also counts against the property in the DPE. That matters if you let it to a tenant, because homes with poor energy ratings are being taken off the rental market in stages from 2025.

Does an older French property have to have a VMC?

Since 1982, new homes have had to be ventilated permanently, and a VMC is the usual way builders meet that rule. It doesn't apply to homes built before then, so an older property doesn't have to retrofit one. The DPE still marks it down if there isn't one.

What to check before buying a property or adding a VMC

• Is there a VMC, is the fan running, and when were the grilles and unit last cleaned?
• Does the quote include extraction in every wet room, and air inlets in the living room and bedrooms?
• Will the installer need to cut a new opening in an outside wall? That needs a déclaration préalable at the mairie (town hall).
• In an apartment building, drilling through a shared outside wall needs the owners' general meeting to vote it through first.

More on ventilation, energy ratings and grants

• DPE: the energy performance certificate that ventilation affects
• MaPrimeRénov': VMC double flux now qualifies only through a rénovation d'ampleur project, not as a standalone measure
• RGE certification: required for contractors installing VMC under a grant scheme
• Cooling and ventilation systems on the Côte d'Azur