Key takeaway
- Bathrooms with no openable window are legally required to have an extractor fan under UK Building Regulations Part F
- New-build homes must have mechanical ventilation in any bathroom with a bath or shower, even if a window is present
- Older homes with windows aren't legally obliged to have a fan, but one is strongly recommended to prevent mould and damp
- The minimum extraction rate required is 15 l/s continuous or 30 l/s intermittent — most standard domestic fans meet this
- Humidity-sensing fans with a run-on timer are the most effective at tackling condensation without any manual effort
Whether you're renovating, moving into a new home, or noticing condensation creeping up your walls, it's a reasonable question. The short answer depends on your bathroom layout and whether it's a new-build — but even where a fan isn't a legal requirement, installing one is almost always worth it.
Is a Bathroom Extractor Fan a Legal Requirement?
Under UK Building Regulations Part F, mechanical ventilation is required in bathrooms in the following situations:
No openable window: If your bathroom has no window that opens, an extractor fan is a legal requirement. Without ventilation, moisture has nowhere to go — leading to mould, damp, and poor air quality.
New-build homes: Any home built or significantly renovated to modern standards (post-2010 airtightness requirements) must have mechanical ventilation in bathrooms with a bath or shower — even if a window is present. Modern builds are highly airtight by design, so a window alone isn't sufficient to remove moisture effectively.
Toilet-only rooms: A WC with no bath or shower can rely on an openable window alone, provided it meets the minimum openable area requirement.
What Extraction Rate Does Building Regs Require?
Part F specifies minimum extraction rates:
- Bathroom with bath or shower: 15 l/s (litres per second) continuous, or 30 l/s intermittent
- Utility rooms: 30 l/s intermittent
Most domestic bathroom extractor fans meet these figures, but check the product specification before buying — particularly for larger bathrooms or rooms that generate heavy steam.
What If My Bathroom Is Older and Has a Window?
If your home predates modern building regulations and your bathroom has an openable window, there's no legal obligation to install a fan. But a window alone is rarely enough to prevent condensation — especially in winter when opening a window after a shower isn't practical.
Even a modest extractor fan running during and for a few minutes after showering will make a noticeable difference to moisture levels and dramatically reduce the risk of mould.
Why Install a Bathroom Extractor Fan?
Eliminate Condensation
Steam from a shower or bath carries a significant amount of moisture. Without extraction, that moisture settles on mirrors, walls, tiles, and ceilings. A fan with a run-on timer continues extracting for several minutes after the shower ends — clearing residual humidity before it condenses.
Prevent Mould and Damp
Mould spores thrive in humid, poorly ventilated spaces. Left unchecked, bathroom mould damages plasterwork, tiles, grout, and sealant — and in worse cases requires full replastering or retiling. It can also aggravate asthma and other respiratory conditions. Consistent extraction is the most effective way to stop mould taking hold.
Protect Your Bathroom Long-Term
Persistent damp eventually works into the structure of the room. By keeping humidity levels low, a good extractor fan extends the life of paintwork, sealant, and fixtures — meaning fewer repairs and a better-looking bathroom for longer.
How to Choose the Right Bathroom Extractor Fan
Match the Extraction Rate to the Room
For a standard domestic bathroom (roughly 5–8 m²), a fan rated at 85–100 m³/hour is typically sufficient. For larger bathrooms, rooms with heavy steam, or spaces with poor natural ventilation, choose something more powerful. If in doubt, go up a size — an oversized fan isn't a problem, an undersized one is.
Prioritise Quiet Operation for En-Suites
En-suites sit next to bedrooms, so noise matters. Look for fans rated at 25–30 dB(A) or below. Inline fans — where the motor sits in the loft duct rather than the room — are the quietest option and worth considering if noise is a concern.
Choose the Right Installation Type
- Wall-mounted: Ducts directly through an external wall. Simple installation, no loft access needed.
- Ceiling-mounted: Common in bathrooms with loft access. Allows ducting to run to an external vent or roof terminal.
- Inline: The motor is positioned within the duct run, away from the bathroom. Near-silent in use; ideal for en-suites or rooms where low noise is essential.
Decide on Your Switching Method
- Humidity-sensing: Activates automatically when moisture levels rise above a threshold. Set-and-forget — no need to remember to turn it on.
- Timer/run-on: Runs for a set period after the light or pull cord is switched off. A practical middle-ground for most bathrooms.
- Pull cord or wall switch: Manual control. Lower cost and simpler to install, but relies on the user remembering to switch on and off.
Browse our full range of bathroom extractor fans, including quiet inline models, humidity-controlled fans, and options from Vent-Axia, Elta, Greenwood, S&P, and Xpelair.
Frequently Asked Questions
Do I legally need an extractor fan in my bathroom?
Yes, in two situations: if your bathroom has no openable window, or if it's in a new-build (built to modern airtightness standards) with a bath or shower. Both scenarios are covered by UK Building Regulations Part F, which requires mechanical ventilation.
What extraction rate do I need for my bathroom?
Building Regulations require a minimum of 15 l/s (54 m³/hour) on a continuous setting, or 30 l/s (108 m³/hour) on an intermittent setting. Most standard domestic fans exceed this. For larger bathrooms or heavy-steam rooms, a fan rated at 100 m³/hour or above is advisable.
Can I rely on a window instead of an extractor fan?
In an older home with an openable window, a fan is not legally required — but it is strongly recommended. Windows alone rarely remove moisture quickly enough, particularly in winter. Condensation and mould are far more likely in bathrooms that rely solely on natural ventilation.
What's the best extractor fan for a bathroom with bad condensation?
A humidity-sensing fan with a run-on timer is the most effective option. It activates automatically when steam rises and continues running until moisture levels drop. Models from Vent-Axia, Elta, and Greenwood are popular choices and available in quiet versions suitable for en-suites.
How long should a bathroom extractor fan run after a shower?
Best practice is 15–20 minutes after the shower ends. A fan with an overrun timer pre-set to this duration handles it automatically, without any need to remember.
Where is the best place to install a bathroom extractor fan?
Position it as close to the moisture source as possible — above or adjacent to the shower. Ideally it should be on the opposite side of the room from the door, so incoming fresh air sweeps across the whole room before being extracted.
Need Further Help?
If you need additional assistance or have questions about choosing the right bathroom extractor fan for your project, feel free to reach out to us at hello@efans.co.uk.