Extractor fan love: Your ultimate guide

Love might be taking it a bit far, but extractor fans are a topic I’m enthusiastic about nonetheless! This may be because I spec’d the wrong one in my own bathroom refurb, which has annoyed me ever since. Or perhaps because I often find myself persuading clients that their extractor fan is not the place to economise.

In every renovation there are areas where cut-backs can be made and others where short-term savings can lead to problems later on. Extractor fans fall into the second category. Installing insufficient ventilation in your bathroom creates a damp, warm environment which is perfect for mould growth. 

According to NHS guidance, if you have damp and mould in your home you are more likely to have respiratory problems, allergies or asthma. Damp and mould can also affect the immune system.

Along with the inconvenience of a steamy room with lots of condensation to clean up, a bathroom that isn’t ventilated properly will age quickly. Peeling paint work, black mildew and rotten wood will ruin your beautiful new bathroom shockingly fast. So, before you splash out on those lovely new tiles, make sure you’ve saved a bit of the budget for a great extractor and all that investment will be worthwhile.

There’s more to extractors than meets the eye (pun intended!), so I’ve created this ultimate guide to help you choose the best for your bathroom…

Do I have to install one?

The answer varies depending on your situation;

  • Are you building a new bathroom / shower room or WC as part of an extension?  Then you must comply with current building regulation standards for ventilation (see link below).

  • Are you carrying out works elsewhere in your home but not altering your bathroom, shower room or WC?  Then you must ensure your new works don’t make your existing ventilation situation worse.   

  • Are you carrying out works to a bathroom, shower room or WC with an existing extractor?  Then it must be maintained or replaced. If there is no existing ventilation system then you are not required to provide one…. but after reading our intro, you might want to! 

What type of extractor should I buy?

There are three main extractor types, each suitable for different installation situations. 

Ultimate-Guide-To-Extractor-Fans-Front-Cover
Project by: Beth Dadswell and Andrew Wilbourne

Surface mounted axial fan

  • Typical extraction rates of between 15 – 25 l/s (litres per second)

  • Typical noise levels - 14 - 41dBA 

  • Maximum duct runs 1-1.5m

  • Price range £20-30

This is your typical basic fan. Axial blades mean that the fan mechanism is fairly slim, creating an unobtrusive option for surface mounting on a wall or ceiling. 

Installation for this type of fan is recommended with a maximum duct length of 1-1.5m (i.e. from the location of the fan to the exterior outlet). Bear in mind that every turn of ducting takes one meter off the suggested length, so this type of fan is really only suitable for a short straight run where bathrooms are located adjacent to an external wall or directly under a roof.

Surface mounted centrifugal fan

  • Typical extraction rates of between 17 - 60 l/s

  • Typical noise levels 26 – 50 dBA

  • Maximum duct runs 5-8m

  • Price range £45- £130

Centrifugal fans are more powerful than the axial and can therefore force air down much longer duct runs; anywhere from 5 to 8 metres depending on the model. This means they are ideal for bathrooms located away from an external wall or roof.              

Remember that you will need to take 1m off the recommended duct length for every turn in the ducting to ensure that the extractor will function correctly.

The mechanism of a centrifugal fan is deeper than that of an axial and most extractors of this type will protrude around 100mm from the wall if surface mounted. If this will ruin the look of your new bathroom then look for a model that can be recess mounted – it will take a bit more work but will look a lot better.

The Acute House by OOF! Architecture - photo Nic Granleese
Project: By OOF! Architecture

Inline mixed flow extractor

  • Typical extraction rates of between 61 - 68 l/s

  • Typical noise levels – 22 - 24dBA

  • Maximum duct runs 8 – 10 m

  • Price range £50 - £125

An inline extractor fan sits within the duct work, usually in a loft space or void, away from the room requiring the extract. One end of the duct is connected to an outlet in the external wall or roof and the other is connected to the bathroom and covered by a grille or valve.   

The most popular type of inline fan for domestic use is called a ‘mixed flow’. A mixed flow pulls the air in an axial and radial direction and is generally more powerful than a simple axial fan.

As the fan itself is situated away from the room it is ventilating, any sensors, such as a humidistat or a PIR sensor, will have to be bought and installed separately. The advantage of its remote location is that the noise level in the room should be extremely low. The disadvantage is that they need to be accessible, so perfect for a loft space or cupboard but trickier if located behind a ceiling with no access.

Due to their simple function an inline fan makes for the most visibly pleasing option. The internal valve can be mounted in any bathroom zone and comes in a range of finishes and designs, making them the most discreet fan option.

How do I know what extraction rate I need?

The ventilation rate of any extractor is marked in the product specifications as either litres per second (l/s) or cubic meters per hour (m3/h). 

To comply with regulations your bathroom, shower room or WC should meet the following ventilation rates;

Bathrooms or shower rooms:

  • intermittent extract which provides 15 l/s ventilation when installed,

  • OR a continuous extract of 8 l/s ventilation when installed.

WCs:

  • intermittent or continuous extract providing 6 l/s ventilation when installed,

  • OR purge ventilation through use of a window meeting the minimum openable area standards (provided security is not an issue). 

Note that the ventilation rates in the regulations are for when an extractor is installed, while rates specified on most extractors are the rate when operated in isolation (i.e. test conditions). 

Any items subsequently added to the extractor, such as ductwork or grilles, will reduce the performance significantly. This means that once installed its operating rate will be much lower.

Should I choose intermittent or continuous ventilation?

  • Intermittent ventilation – This is the most popular type of extractor which just turns on when you need it.   

  • Continuous extract – A continuous extractor runs at a lower, consistent rate in the background.  It’s a less common option but worth considering.

Whether through the addition of double glazing, the tighter construction of newer builds, or the growing number of bathrooms and shower rooms without windows, our bathrooms are becoming more air tight. The upside to this is cosy rooms with no nasty drafts when we get out of the shower. The downside is a lot of trapped moisture in the air that can’t escape. Any bathroom that doesn’t have background ventilation, such as trickle vents on a window, is at higher risk of condensation and mould growth and should consider a continuous extract. 

Advantages are that these require slower speeds and so are quieter, therefore less obtrusive, and continuous extractors can also be very cost efficient.

How will my extractor fan turn on?

Extractors can be operated manually and/or by automatic sensor. Some extracts will have a choice of operating settings, others may have only one option. Any automatic control should have a manual override to allow the occupant to turn the extractor on.

  • Pull Cord

    The simplest option to install is an extractor with a pull cord mounted directly on the unit itself, allowing the manual turning off and on of the extractor. Alternatively, you can always install any extractor with a separately mounted pull cord if required.

  • Turns on with the lights

    This is the most popular option with our building projects and requires your electrician to wire the extractor to the lighting circuit. If you are rewiring your bathroom as part of the works, our top tip is to allow yourself two lighting circuits; one that switches on a main light with the extractor, and the other just a small task light for night time bathroom trips. 

  • Humidity Sensor

    A humidity sensor will turn on an extractor when the moisture level in the air reaches a certain value. This is great if you have family members who keep forgetting to turn the extractor on at all! 

  • PIR sensor

    This is a motion sensor that will turn on an extractor when someone enters the room. 

  • An app

    Yes, home automation has reached extractor fans too! It may seem a bit bonkers but there are advantages. The app allows you to set more complex operating functions, such as the fan not coming on between certain hours, or to adjust the delay start timer at night. Another advantage is that it can be turned on using a light sensor, meaning you can have the extra functionality without the need to physically wire it in to your lighting circuit. Perfect for a high achieving upgrade to an existing basic model.

Other features to look out for

  • Run on timer

The extract fan will continue running even after it has been switched off to ensure that all moisture is extracted after you’ve left the room. Most extractors on the market have this as an option, some with varying time adjustments between 5-30 minutes, and we would recommend this as a must have feature. NB. A run on timer of 15 minutes is a building regs requirement in rooms with no openable window.

  • Trickle ventilation

Allows the extractor to provide a continuous low level of extract when not in use and only boosts to maximum power when required. All rooms should have a level of background ventilation, so this is perfect if you have a bathroom with without windows or with poor ventilation.

  • Delayed start timer

This neat little feature delays the timer from starting within 2 minutes of turning on, meaning a quick bathroom trip in the middle of the night won’t wake the whole house.

  • Silent / quiet fans

Extractors marketed as being quiet or silent usually have a noise level of around 14dB(A) when operating at their minimum speed of 15 l/s. Note that these fans often have 2 speed options and the low noise value may only apply for the lower setting.

  • Back draft shutters

The purpose of a back draft shutter is to stop air coming from outside and into your bathroom. These are integrated in some extractors, but if you are using an inline fan you will need to purchase one separately. These are only suitable for wall mounted extractors and any backdraft shutters should be removed if ceiling mounted as the weight will stop the extractor from functioning.

  • SELV (Safety Extra Low Voltage)

Extractor fans are electrical and most models will need to be fitted in bathroom Zone 2, (see below for a zone diagram).

If you do need to install a fan in Zone 1 (the immediate area round the bath or shower) then you will need to install a Low Voltage or SELV (Safety Extra Low Voltage) model. Something to note is that in order to be low voltage the extractors come with a little transformer box that will need to be mounted in an accessible location away from the unit itself, so plan this with your electrician before install.

So which one is right for me?

These common scenarios should help you to choose the right extractor for your situation:

1) Your extractor will sit on or near an external wall, with a duct leading straight out

With ducting of less than 1m, an axial fan will be fine for you! We’d always recommend that you go with a minimum of 21 l/s as standard. 

2) You need a quiet extractor

  • If you’re in the situation above then no problem – axial fans are less powerful and usually quieter than their centrifugal counterparts. There are lots of ‘quiet’ or ‘silent’ axial fans available which operate at low noise levels.

  • If you need a more powerful extractor due to a longer duct then consider an inline extractor. These tend to be better insulated and due to their location away from the bathroom won’t be audible when turned on.

  • Get an extractor with a continuous extract setting. By running continuously your extractor will operate at a quieter low level.  

3) You don’t want your fan waking everyone up in the night!

  • You can buy any extractor that has a delay start timer so that it doesn’t turn on for a couple of minutes, meaning you can pop to the toilet without setting the extractor off.

  • Any extractor can be wired to turn on with the lights. By having a smaller light on a second circuit, you can avoid turning on the extractor, and painfully bright lights, on night-time visits.   

  • Get an extractor with a humidistat sensor that turns on only when there’s moisture in the room, and therefore not in the middle of the night.

4) We need an extractor close to the bath or shower (bathroom zone 1)

It’s always good to locate your extractor close to the source of steam, so if that requires fitting your extractor in bathroom zone 1 there are a couple of options available to you:

  • You need a low voltage extractor marked SELV (Safety Extra Low Voltage) which are suitable for installation in bathroom zone 1. (See our note above about the separate transformer box).

  • If you have duct work and a suitable space for installation, get an inline extractor. As the extractor is mounted away from the bathroom itself, the air inlet valve or grille can be mounted anywhere in the bathroom.

5) We have an internal bathroom with no windows

You will probably need a longer duct run so a centrifugal or inline extractor would be most suitable. Consider one with a continuous extract setting for much needed additional ventilation.

6) I want an aesthetically pleasing extractor

If you have a suitable space to install one, then the best option for an unobtrusive or coordinating finish would be an inline extractor, with the wide range of grilles and valves available. 

Project by: Hobbs Jamieson Architecture
Via Pinterest

Can I install one myself and do I need building regs approval?

Replacing an item of electrical equipment on a ‘like-for-like’ basis does not have to be done by a registered electrician or approved by building regulations, UNLESS it is in a ‘special location’, i.e. in the immediate vicinity of the bath or shower, (see Part P of the regs for a diagram).  Only attempt to carry out works yourself if you feel confident to do so and make sure you turn off all the electrics at the consumer unit before you start!

If you’re installing a new extractor, or your replacement extractor requires additional wiring such as a new connection to a lighting circuit, then the work should be carried out by a registered electrician. Your electrician will be able to self-certify the works to ensure it complies with Part P of the building regulations.

Whether replacing an existing extractor yourself or using a professional you should consider the following installation issues;

Bathroom zones

Check the IP rating (stands for International Protection marking) on the extractor specification to see which bathroom zone it can be installed in. We’ve talked about the need to use a Low Voltage, SELV or inline extractor if you must install in bathroom zone 1.

Location

For best air flow try to install your extractor close to the source of steam, but as far away as possible from the air intake of that room, which might be the door or a window with trickle vents.

Ducting

Any extractor should be installed to exhaust air to the outdoors, either through a duct or directly through a wall or window. Rigid ducts, rectangular or circular, should be used wherever possible. Where necessary, flexible ducts may be used, but its length should be kept to a minimum, connecting to rigid ductwork at the earliest opportunity. Flexible duct should be pulled taught to ensure that the full internal diameter is obtained and flow resistance minimised. This is considered to have been achieved if the duct is extended to 90% of its maximum length. Ducting should be insulated where it passes through unheated areas and voids (e.g. loft spaces) with the equivalent of at least 25 mm of a material having a thermal conductivity of ≤0.04 W/(m.K) to reduce the possibility of condensation forming.

Let the air in! ​

Don’t forget that if you want your extractor to function properly you must ensure that air can be drawn into your bathroom to replace the air being sucked out. This is why building regulations specify that your bathroom door should have a minimum 10mm cut under to create enough of a gap to allow the air through. If you don’t know your finished floor level when fitting your door then allow 20mm just to be sure.

Still want to know more?

If all that wasn’t enough for you and you still want to know more, you’ll enjoy the Government’s regulations and compliance guides below!

Our HomeNotes Journal is here to bring you clear and up-to-date information for Homeowners renovating their homes.

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