Installing ventilation in the bathroom: the complete guide

A poorly ventilated bathroom means condensation on the mirror, walls going mouldy, lingering odours and a high humidity level that eventually degrades the paintwork and sealants. The lasting solution is simple: install mechanical ventilation that extracts the damp air towards the outside. Depending on your situation, it may be a simple wall extractor fan or a central mechanical ventilation system (MVHR) for the whole house. The job is within reach of a methodical DIYer.

Understanding the ventilation options

There are two main solutions. The standalone extractor fan, installed in an exterior wall or a window, extracts the air from only the room where it is fitted: simple and inexpensive, it is often enough for a bathroom. The mechanical ventilation system, on the other hand, manages the extraction of several damp rooms (bathroom, kitchen, WC) with a network of ducts to a central extractor located in the loft or a utility room. The choice depends on your home and what already exists.

The necessary tools

• An extractor fan for the bathroom with a non-return flap (50 to 150 € depending on the flow rate and options).
• For the mechanical ventilation system: an extraction unit, ducts, vents and an electrical connection.
• A drill bit and a hole saw to drill the wall or window (use a hole saw suited to the vent's diameter).
• Sealant or expanding foam to seal the passage of the duct through the wall.
• Suitable electrical wire, a circuit breaker and possibly a switch or a humidity detector.
• A screwdriver, a drill, a spirit level and a tape measure.

The steps for installing a wall extractor fan

1. Switch off the electricity at the consumer unit before any work near water: it is an absolute safety rule, because the bathroom is a damp room.
2. Choose the location: ideally in the exterior wall, opposite the air inlet, at shower height or above the door depending on the model.
3. Drill the wall with the hole saw at the duct's diameter, drilling from the outside towards the inside if possible for a clean hole.
4. Insert the duct (or the vent), seal the perimeter with sealant, and fix the extractor fan to the wall.
5. Connect the electricity respecting the standards: a dedicated switch or, better, a connection on the lighting circuit, and a non-return flap if the extractor is fitted with one.
6. Connect the circuit and test the air flow by placing a sheet of paper under the vent: it must be sucked up.
7. Restore the power and check there are no vibrations or abnormal noise.

Installing a mechanical ventilation system: when to call in a professional?

Installing a complete mechanical ventilation system involves fitting a unit, running ducts through the loft, drilling the ceilings and making a more complex electrical connection. If you are comfortable with plumbing and electrical work, it is doable over several days, but running the ducts in a false ceiling or bringing the electrics up to standard often justify a professional's intervention. A quote for a single-flow mechanical ventilation system generally ranges between 600 and 1,500 €, installation included.

The mistakes to avoid

• Installing the extractor in an interior wall or above a water passage without checking the extraction direction: the air must go out towards the outside.
• Neglecting the air inlet: an extraction only works well if fresh air can enter (a low grille or an ajar window).
• Working without switching off the power in a damp room: it is a serious electrical risk.
• Choosing an extractor too small for the room: its flow rate must match the volume of the bathroom.
• Forgetting the non-return flap: without it, cold air and odours can come back into the room when the extractor is off.

Maintaining your ventilation

Ventilation only works well if it is maintained. Clean the grille and the blades of the extractor every two to three months with a damp cloth, check the flap, and have the mechanical ventilation system checked once a year, in particular the filter and the ducts, which get dirty with dust and grease. Simple regular dusting avoids breakdowns and maintains an effective air flow.

Installing ventilation in your bathroom is one of the most useful investments for the health of your home: it eliminates condensation, prevents mould and freshens the air on a permanent basis. Whether you choose a simple wall extractor, within your reach in one day, or a complete mechanical ventilation system, think first of electrical safety and correct sizing. With well-installed and maintained ventilation, your bathroom will stay healthy for years.