Bathroom ventilation (UK Part F): the simple homeowner guide
A great bathroom isn’t just tile and brass—it’s air that clears quickly so mirrors defog, grout stays clean, and the room doesn’t smell like yesterday’s shower.
In the UK, the common-sense rules live in Approved Document F (“Part F”). Here’s the calm version: the airflow you actually need, which fan type suits real homes, where to put it, and how to plan everything so Building Control smiles.
What airflow do I actually need?
Part F gives you two compliant routes:
- An intermittent extractor (the classic on-with-the-light fan) that moves around 15 l/s when it runs
- A continuous system (dMEV/MEV/MVHR) that extracts quietly all the time and boosts to ~8 l/s or more when you shower
Both paths work. The right choice depends on your home and habits—not on chasing a bigger number.
Intermittent vs continuous: which suits my home?
Intermittent fans are simple and cost-effective. They switch on with the light or a pull cord and run on after you leave to finish the job. They’re great for smaller homes with occasional showers.
Continuous systems hum away quietly, then boost during steamy moments. They shine in airtight homes and busy morning queues because moisture never gets a head start.
If you’re planning a doorless layout, pairing a steady background extract with a boost keeps the whole room calmer.
Where should the fan go (and how should it be ducted)?
- Mount the fan high on the wall or ceiling—steam rises
- Use a short, straight duct run to outside so it breathes properly
- Avoid unnecessary bends—they add noise and reduce performance
- Larger-diameter ducting is quieter and shifts more air at lower speed
- If the outside wall is windy, aim the terminal to a calmer face or choose a constant-volume unit so extract doesn’t yo-yo on breezy days
Do I still need trickle vents and door undercuts?
Yes. Extraction only works if fresh air can get in.
- Keep background ventilators (trickle vents) in habitable rooms
- Add a small undercut at the bathroom door so air can move toward the fan
It’s a small detail that makes a big difference. The fan clears steam faster—and you’re less likely to switch it off.
Plan the room once, not twice
Decide your shower footprint and screen line first. Then position the fan so it pulls steam away from the opening, not across the room. If you’re weighing up a doorless layout, our guide to walk-in shower size in the UK explains why 1200 × 800–900 mm footprints behave better - and make ventilation’s job easier.
Noise, controls and everyday usability
If a fan is shouty, people disable it.
- Choose a good-quality, quiet unit
- Use bigger, straighter ducts
- Match the control to your routine:
- Timer if you like simple
- Humidistat if you forget
- Boost button for back-to-back showers
The goal is the same: clear the room without reminding the neighbours you’ve had a wash.
“Can I just open a window?”
Windows help for a quick purge - but they’re no substitute for mechanical extract to outside.
You’ll still want a fan, especially in winter, when no one opens the window long enough to do any good.
A 2-minute planning checklist
Confirm your airflow route:
- Intermittent (around 15 l/s)
- Continuous with boost (~8 l/s+)
- Site the fan high
- Keep the duct short and straight
- Plan background air via trickle vents and a door undercut
- Lock your shower layout first so the fan works with it, not against it
If you’re coordinating lighting too,the same principles from our kitchen ceiling lights guide:
- Clear task light
- Gentle ambient light
- Sensible switching
(Just mind the electrical zones.)
The Beams way
We design ventilation with the room—not after it. Shower size, screen, fan and duct all decided together so the mirror clears and the floor stays dry.
We commission the system so the numbers on paper match the air in the room, then wrap it into a fixed proposal—no “while we were there” surprises.
If you’d like a joined-up plan, start with bathroom renovation and tell us how you live - we’ll take it from there.