Single-flow or double-flow VMC: understand the difference
Mechanical ventilation (VMC) renews the air in a home and clears the humidity produced by everyday use. Single-flow and double-flow systems share that objective but use different duct arrangements and require different amounts of space.
What does a VMC do?
It removes stale, humid air from selected rooms (kitchen, bathroom, toilet) and supports regular air renewal throughout the home. Insufficient ventilation can encourage condensation and damp, but the choice of system needs to suit the building.
Single-flow VMC
A single-flow system extracts air through ductwork connected to wet rooms. Fresh air enters through designated air inlets in the other rooms.
Strengths
- relatively simple network;
- generally smaller footprint;
- a common choice for renovations.
Points to anticipate
- unit position;
- duct routing;
- extraction terminals;
- air inlets;
- access for maintenance.
Double-flow VMC
A double-flow system manages extraction and fresh-air supply with two duct networks. It organises the route of fresh air through the building more fully.
Possible strengths
- fuller management of air flows;
- heat recovery depending on the system.
Constraints
- larger duct network;
- more space required;
- more precise design;
- servicing of the unit and its filters.
Which is easier during renovation?
Available space is often decisive. Accessible roof space or suspended ceilings can make duct routing easier. A completely finished interior may make a double-flow network more difficult to integrate — this is generally planned alongside the other trades of an interior renovation, in particular the drywall and lining work.
Does noise depend only on the fan?
No. Airflow, duct layout, terminals and installation quality can also affect sound.
Is double-flow always better?
No. More complexity is useful only when it suits the property, budget, available space and actual needs.
Key point
Single-flow: extraction with a simpler network.
Double-flow: extraction + supply with a more extensive network.
A visit or assessment shows what can genuinely be integrated into your home.