A beautiful new bathroom can quickly lose its shine if steam and moisture are not properly controlled. Installing the right bathroom extractor fan and ventilation system is essential to prevent mould growth, protect paintwork, tiles, and joinery, and keep your bathroom fresh and comfortable for years. Effective bathroom ventilation reduces condensation, stopping damp and unpleasant smells from building up.

Whether you choose an intermittent or continuous extractor fan, the key is to ensure moisture is extracted efficiently. Proper ventilation is especially important after a bathroom refit to safeguard your investment and maintain a healthy, mould-free environment.

How bathroom condensation builds up

Every hot bath or shower releases a lot of warm, moist air into a relatively small space. When that moisture hits cooler surfaces such as mirrors, tiles, windows and ceilings, it turns into water droplets.

Over time, this repeated cycle of steaming and cooling leads to stained paintwork, swollen woodwork and eventually mould. Modern bathrooms are often well sealed with double glazing and tight doors, so the moisture has nowhere to escape without proper extraction.

Choosing between intermittent and continuous fans

Most homes have an intermittent fan. This type of fan comes on when you use the light switch or a separate switch, then turns off again after a short period. It is simple and familiar, but relies on you remembering to use it for long enough.

Continuous fans run gently in the background all the time, then boost to a higher speed when needed. They are usually quieter, use very little electricity on the lower setting and are effective in bathrooms that see frequent use or have limited natural ventilation.

Intermittent – runs only when switched on, higher airflow for short bursts
Continuous – trickle ventilation all day, boosts when humidity or a switch tells it to
Best for busy homes – continuous fans suit households where the bathroom is used throughout the day

For small shower rooms and internal bathrooms, a continuous fan can make a noticeable difference by keeping background humidity under control rather than just reacting to steam after it appears.

Controls: timer fans versus humidity sensors

A timer fan keeps running for a set period after you switch the light off. This helps clear moisture that lingers once you have finished using the room. An electrician can usually adjust the overrun time so it suits how your household uses the bathroom.

Humidity-sensing fans use a built-in sensor to detect when moisture levels rise. They then switch themselves on or boost automatically, and drop back once the air has dried out. This suits homes where people often forget to use the fan, or where showers are taken at different times of day.

Many modern extractor fans combine timer and humidity functions. During a refit, your installer can help you match the controls to your family’s habits so the fan does its job with minimal effort from you.

Ducting and outlet: getting the air outside

Even the best extractor fan will struggle if the ducting is poorly planned. Moist air needs a clear, direct route from the fan to the outside of your home.

Short, straight duct runs are ideal, as each bend reduces airflow. Where bends are unavoidable, they should be smooth and kept to a minimum. Rigid ducting is often better than flexible, because it maintains its shape and internal diameter.

Moist air should always be vented outdoors, never into a loft, ceiling void or cavity. Venting into a roof space can create severe damp and mould in the structure of your home. A good installer will position the external grille to suit the building, taking care with details such as weatherproofing and preventing backdraughts.

Make-up air: letting fresh air in

For extraction to work well, replacement air needs to get into the bathroom as stale, moist air is removed. This is known as make-up air. Without it, fans can become noisy and far less effective.

Typically, there should be a small gap under the bathroom door or a discreet grille that allows air to flow in from the hallway or adjacent room. During a refit, this is a simple detail to get right and it has a big effect on overall performance.

This is particularly important in London flats and internal bathrooms with no external window, where the fan and ductwork are the main route for air movement.

Extra care for shower rooms and wet rooms

Shower rooms and wet rooms create more moisture in a shorter space of time than traditional bathrooms. The walls and floors are often fully tiled, which can hide the early signs of damp behind the surfaces.

In these spaces, higher-capacity fans or continuous mechanical extraction are usually sensible. Positioning is also crucial: the fan or intake should be located where it can capture steam as it rises, often near or directly over the shower area, while still complying with electrical safety zones.

Signs your bathroom needs better extraction

You do not need specialist equipment to spot that a fan is not coping. Your bathroom will usually give you clues that moisture is lingering for too long.

Black mould on silicone, grout lines or around window frames
Peeling or flaking paint, especially on ceilings and outside shower areas
Persistent misting on mirrors and windows long after a shower
Musty smells that do not go away even after cleaning

If you notice these issues, check that the fan grille is clean, the isolation switch is on and the duct outlet outside is not blocked. Hold a piece of light tissue near the fan while it is running; if it barely moves, extraction may be poor.

Simple habits to reduce moisture build-up

Good ventilation starts with the fan, but your daily routine also makes a difference. A few small changes can support the system and protect your finishes.

Keep the bathroom door mostly closed when showering so steam is drawn towards the extractor, not into the hallway. After you finish, leave the fan running for at least 15 to 20 minutes or let the timer overrun complete its cycle.

Wipe down shower screens, tiles and horizontal surfaces with a squeegee or towel to remove surface water. If there is a window, open it slightly after showering, but avoid turning the fan off early – a combination of gentle natural ventilation and mechanical extraction works best.

Best time to upgrade your fan and electrics

A bathroom renovation is often the ideal time to improve ventilation, as surfaces are already being stripped back and access to ducts and wiring is easier. This makes it simpler to change fan positions, run better ducting and add new controls such as humidity sensors.

Electrical work in bathrooms must comply with Part P of the Building Regulations and should be carried out by suitably qualified tradespeople. Your builder or bathroom installer should coordinate fan sizing, duct routes and electrics as part of the overall design, rather than treating the fan as an afterthought.

Getting this right during a refit can greatly reduce the risk of damp, mould and damaged finishes later, protecting your investment and keeping the space healthier for your family.

Plan ventilation into your bathroom refit

If you are planning a new bathroom, shower room or wet room, it is well worth designing the ventilation alongside the layout and finishes. The right extractor fan, ducting and controls will help keep your new space looking and feeling fresh.

Riverside Construction Group can plan bathroom ventilation as part of a complete installation, ensuring extraction, make-up air and electrics all work together safely. To book a survey and discuss how ventilation can be built into your refit, contact Riverside Construction Group on 02031481518 or visit our bathroom installation pages.

Bathroom Ventilation: Choosing the Right Extractor Fan