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Choosing a Bathroom Extractor Fan

The following guide will take a few minutes to read but covers everything you need to know when choosing a bathroom fan. 

The Basics:
1. Wiring regulations and Bathroom Zones
2. Switching and Operation Options
3. Size and Extraction Rate
4. Comfort - Noise and Aesthetics
5. Two Fans which cover 95% of all bathroom installations

Further Reading:
6. Centrifugal Extractor Fans
7. Intermittent Extraction v Continuous Ventilation

1. Wiring regulations, bathroom zones and extractor fans

Electricity and water make for a dangerous combination so the UK Electrical Wiring Regulations divide the bathroom into three zones relating to their proximity to water sources. This determines the type of fan you may install in each zone.

Let us first look at the zones:
  • Zone 1 is in the shower or the area vertically 2.25m above the bath.
  • Zone 2 extends in all directions for 0.6m (60cm) from Zone 1.
  • Zone 3 extends laterally for a further 2.4m from zone 2.
  • Anything outside this area, or outside the bathroom - for example the loft above, is outside the zones.Bathroom Zones
Extractor Fans and Zones

Zone 1 and Zone 2 
  • There are only two types of fan which may be installed in Zones 1 and 2. They are:
    •  ALL SELV fans (Safety Extra Low Voltage). Also known as 12v fans or LV fans, they require a transformer, (housed in zone 3 or outside the zones) to reduce the mains voltage (240v) to 12v. Usually, but not always, the transformer is supplied with the fan.
    • Any fan, regardless of voltage, that has an IP45 rated motor. 'IP' means 'Ingress Protected' and a rating of IP45 signifies that the motor, and indeed all electrical parts, are 'resistant to jets of water from all angles'.
  • Any fan rated for zones 1 and 2, by default, may be installed in zone 3.
  • ALL electrical works must be carried out by a fully qualified, professional electrician.
​Zone 3 and Outside the Zones
  • Any extractor fan, regardless of voltage or IP rating may be installed here as these areas are deemed a safe distance from the principle sources of water, the bath and shower.
  • Inline fans are another type of extractor fan which are installed in the loft space above the bathroom. A length of ducting connects the fan to the bathroom. Since the fan itself is housed remotely, outside of the zonal area, with only a plastic grille in the bathroom ceiling, they too are suitable for extracting from any bathroom zone.
  • A number of fans, such as the Vent Axia Silhouette, Manrose XF range and Airflow Icon are available in both SELV and 240v versions.
  • ALL electrical works must be carried out by a fully qualified, professional electrician.

2. Switching and Operation Options

All fans maybe wired into the lighting circuit, so that they turn on and off with your lights, or a separate remote switch, allowing them to be operated independently. Further to that, extractor fans have a range of extra switching options which suit different applications and requirements. Many fans are available in three versions - Basic, Timer and Humidistat, but some ranges also have pull cord and PIR versions.
  • Basic models are operated by the light or remote switch only.
  • Timer models feature a timer which keeps the fan running for a set period after the light or remote switch is turned off. This ensures all steam has been extracted from the bathroom.
  • Fans with Humidistats will turn on automatically when humidity in the bathroom reaches a pre-set level and off when the humidity falls back to its preset level. These are great in bathrooms where the lights (and fan) are not always turned on manually and are popular with landlords, or in those installations where a fan is only required to extract steam.
  • Fans with integral Pullcord are rarer these days, but allow for local operation.
  • PIR (Passive Infra Red) sensors operate the extractor fan automatically when somebody enters the room.

3. Size and Air Extraction Rate

Domestic bathroom extractor fans come in two sizes: 4 inch /100mm and 6 inch / 150mm. In almost every case a 4 inch bathroom extractor fan will suffice. Six inch fans need only be considered in bathrooms greater than nine metres squared, or where special circumstances require a more powerful fan,…such as bathrooms with no natural ventilation or particularly cold, north facing bathrooms.
Measured in 'Litres per Second' (L/s) or 'Metres Cubed per Hour' (m3/hr), the air extraction rate of a bathroom extractor fan is one of the most important considerations. The Building Regulations stipulate that a bathroom extractor fan must extract at least 15L/s in a standard domestic bathroom. Most 4 inch bathroom extractor fans far exceed this minimum requirement, and nowadays the standard is 85m3/hr. Any bathroom extractor fan with an extraction rate of 90m3/hr or above may be considered powerful.

4. Comfort - Noise and Aesthetics

Typical dB measurements for axial extractor fans range between 35dB(A) and 45dB(A) with the more powerful centrifugal fans between 40dB(A) and 55dB(A). In recent years however the trend has moved towards quieter fans and now fans, such as the QT100 discussed earlier, are whisper quiet at 24dB(A)
Remember: you are likely to see this fan everytime you use the bathroom. The money you saved on it when purchasing will soon be forgotten, so don’t install an ugly fan just because it’s cheap. Homeowners are spending more in making their bathrooms beautiful with cool lighting and funky fixtures and fan designs have improved immensely. The old ‘box with grilles’ is slowly being replaced with unobtrusive and subtle ‘tile’ type designs which sit comfortably with any bathroom aesthetic.

5. The Two Best Bathroom Fans Available 

The following two fans cover 95% of all the bathroom installations we specify and supply. Below is a brief description of their basic attributes. Click 'view item' to see detailed information and our product reviews.
Silent Tornado ST100 - High Power 4 inch Axial Fan
Tornado Bathroom Fan Vital Statistics: 97m3/hr / 26L/s : 25db(A) : 7.5w

- IP45 rated motor, so the fan can be installed in any zone in the bathroom without the need for a separate transformer.
- Most powerful 4inch axial fan on the market @ 97m3/hr 
- Low energy. On full power it uses only 7.5w! 
- Virtually silent. 25db(A)
- The best 4 inch axial fan we have ever tested. Click on the 'view item' buttons on the right to see the full specification and read our review.
Standard Model: ST100B
Timer Model: ST100T
Humidistat Model: ST100HT
Pull Cord Model: ST100PC
PIR Model: ST100PR
Manrose MF100 - Inline 'Mixed Flow' Fan
Manrose MF100T Inline Extractor Fan Vital Statistics: 245m3/hr / 68L/s : 24db(A) : 25w

- Installed above the bathroom in the loft or ceiling void.
- With a whopping 245m3/hr extraction rate it's the most powerful 4 inch fan on the market.
- Mounted in the loft above the bathroom, this inline fan can be ducted from directly above the shower or bath. 
- Using only 25w it's very energy efficient.
- Incredibly quiet, particularly so considering its power.
- Extracts steam before it condenses.
- No electrics, impellar or fan casing in the bathroom - just a discreet, flush, circular grille.
Standard Model: MF100S
Timer Version: MF100T

6. Centrifugal extractor fans

In your research you may have come across the term 'centrifugal extractor fan'. This is a special type of fan which uses a totally different impeller design to generate higher exhaust air pressures. In simplified terms - the old/stale/moist air extracted from the room is pushed harder down the length of ducting to the outside world.

This is particularly useful in situations where the fan sits at the end of a long duct run, over 10 metres, for example in internal, basement or en suite bathrooms. Whilst centrifugal and axial fans use consistent impeller sizes such as four and six inch for domestic installations, centrifugal fans are larger than axial fans. They also tend to look 'boxy' as they necessarily sit proud of the wall in order to accomodate the much deeper impeller.

You should now have all the info you need to choose your own fan, but if you'd still like some help, then we'd be really pleased to talk to you. Just call us on 0845 683 0503.

7. Intermittent Extraction v Continuous Ventilation

Despite changes in trend in recent years, intermittent extractor fans are still by far the most common type of air movement device. Intermittent extraction is the movement of air at specific times of need when air is polluted or full of water vapour - for example when someone is cooking or taking a shower. Crucially, the ventilation unit, either manually or automatically, switches on and off - it does not run all the time.

Continuous ventilation has become more popular in recent years as the Building Regulations - particularly Part F (Ventilation) - have demanded greater control over the air coming into and out of properties. Specifically, as buildings have become better insulated and more air tight, in the drive for more efficient energy usage, they suffer more often from lack of fresh air. Before double glazing and precision engineering natural drafts kept our buildings ventilated and in the absence of this natural air movement we have turned increasingly to Continuous Ventilation.  

Mechanical Extract Ventilation - MEV

MEV refers to extract units which simply expel stale air (continuously). Operating at low flow rates of between 50m3/hr and 65m/hr MEV units keep air flowing through a room or building, acting rather like a small window. This is known as Trickle. Some MEV units can switch to a more powerful setting - up to 80m3/hr for example, at times of specific demand. This is known as Boost.

Mechanical Ventilation Heat Recovery

MVHR is increasingly popular and the ventilation industry is investing heavily in this technology. MVHR units use a heat exchanger to bring warm fresh air back into the building to replace the warm heated air that was expelled. MVHR systems were developed to solve the problem that continuous ventilation causes - lost heat and energy wastage. Currently they are more common as 'Whole House Ventilation' units, in which a central, usually rather large, unit with multiple duct points, extracts and replaces air from multiple rooms. However, as the sector grows we are seeing more 'Single Room Heat Recovery' units which look a lot more like tradtional extractor fans.

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