Noise Levels Explained

Noise Levels Explained

One of the most common queries we get is about how loud an extractor fan is going to be when installed and running. This is a very difficult question to answer, but in this blog post, we will look at all the factors and variables that can affect the perceived volume and ways that you can minimise nuisance noise.

Before we get started, the list below shows the quietest fans by type that we sell for different household applications:

Axial Fan Options

Bathroom Fans: Silent Tornado / Envirovent Silent100 / Airflow QT100
Utility Room Fans: Airflow QT120 / Envirovent Silent125
Kitchen Fans: Vent Axia VA140 / Envirovent Silent150

Continuous Flow Fan (dMEV) Options

For all rooms: Monsoon dMEV / Vent Axia Svara / Envirovent SILDUAL
Utility Room & Kitchen Fans: Vent Axia Quadra / Vent Axia Centrif Duo

Inline Fan Options

For all rooms: Tornado Turbo Tube / Envirovent SILMV / Vent Axia ACM

Centrifugal Fan Options

Bathroom Fans: Envirovent Cyclone SELV / Vent Axia Solo Plus SELV
Utility Room & Kitchen Fans: Envirovent Cyclone / Vent Axia Centrif Duo / Vent Axia Quadra

So where do we start?

Every fan on our website will show a noise rating measured in decibels (dB). Decibels as a measurement of sound can be confusing, as the linear rise in decibels does not correlate to the logarithmic curve that tracks the perceived volume we hear as humans. Effectively, the best way to describe how we perceive sound is that the perceived volume we hear doubles every 10dB. In the graph below for example, the x axis shows the rise in dB in increments of 10 and the y axis shows the perceived volume in terms of how many times louder each 10dB increment is heard.

This shows that at 10dB the perceived volume is 2, at 20dB the perceived volume is now 4, at 30dB we have raised to 8, at 40dB we have doubled to 16 and so on. This creates an exponential curve of perceived volume which means where the difference between say 20dB and 30dB is negligible in terms of what we hear (4 to 8 on our scale above) it is vastly different to the difference between say 90dB and 100dB which would be the difference between 512 and 1024 on our scale.


On this chart, we have created a visual scale to give you a real world representation of these perceived volume levels as a guideline for you when looking at the dB level for a fan. Taking the examples we used before, this equates to the difference between 20dB and 30dB as the difference between rustling leaves and a whisper, whereas the difference between 90dB and 100dB is the difference between a hairdryer and a helicopter!

For the most part, when it comes to extractor fans, we are unlikely to look at anything above 50dB unless we are talking about commercial units - but this is where we hit a snag. The dB ratings on the fans are an average dB reading taken from a distance of 3m while the fan is not attached to any ducting and in an environment that gives a true dB level unaffected by variables such as natural amplification or additional noise pollution affecting the readings taken. This is great for giving a level that can be compared against other units including from varying manufacturers, but it means that this level is not a true representation of how the fan noise level will be perceived once installed in your home.

Let’s take two examples and look how two different installations in two different environments could affect how the fan’s noise level could be perceived differently.

Inline Fans and ducted installations

In the first example, let’s take an inline fan installation. Typically, this will be installed in a loft space with an internal grille placed in the ceiling of the bathroom above the shower area. Ducting is then run from the grille to the intake side of the inline fan which then blows the extracted air through another run of ducting to an external vent which could be installed in a gable end wall, soffit or roof venting kit.



As soon as ducting is attached to the inline fan unit the noise level will rise. This is due to the noise created by the airflow through the ducting which is now constricting the airflow into this channel. As the air is pulled through the ducting it will create noise through friction as it passes over the internal surface of the ducting. These soundwaves also ricochet off the internal duct surface which can also amplify them, also adding to the perceivable volume. The length of the ducting being used will affect the overall volume difference.

So what can we do to minimise this additional volume? Firstly, if possible, use solid ducting as the smooth inner surface will minimise friction as the air travels through the ducting. This isn’t often a viable option when installing inline fans, as running solid duct can be problematic when obstacles in the form of beams and joists etc. can hinder a straight line run and although there are connectors that can be used to create bends in the ducting it is worth noting that every 90 degree bend in ducting is equal to an additional metre in terms of air resistance. All fans will have a maximum distance they can duct happily without putting undue strain on the motor unit due to the resistance created so additional bends can create issues all of their own. Therefore, if flexible ducting is being used for a more direct run, it is important to make sure that the ducting is pulled as taut as possible to maximise the inner diameter of the ducting and to reduce the peaks and troughs that can appear when the ducting is left slack. These issues with slack flexible ducting can add to the airflow noise so minimising these will help with the perceived noise level of the extraction.



Picking the correct internal and external grilles is also important. Internal grilles should be fixed apertures with the least amount of obstruction to the airflow - we suggest the following option which is available in varying sizes and either white or chrome finishes. These grilles offer very little resistance to the air being pulled through by the fan unit which also helps to minimise additional noise from the airflow.


There are other options available for internal grilles called Diffuser grilles - these have a central cap that can be spun in and out to adjust the airflow and are predominantly designed to be used with multi-room venting installations to allow you to control airflow over multiple rooms. These are not suitable for installation with inline fans as even when the central cap is spun all the way out, the air has to pass the cap which not only obstructs the full potential air flow but can also cause additional whistling noise due to the higher extraction rate offered by inline fans.

It is also worth noting that it is best to avoid metal grilles in general as the high concentration of humid air that will be drawn to and through the grille accelerates corrosion.

We will look at suitable external grilles when we move on to our second example as this will be relevant for all installation options.

There are other possible variables that we can adjust to help with perceived noise, especially with inline fans. Airflow is crucial when it comes to fans and starving a fan of airflow will add to the perceived noise - think how the sound of your vacuum cleaner changes when you put your hand over the end of the hose! Making sure there is a good flow of air back into the room from the rest of the house will not only improve the extraction but also help minimise extra fan motor noise too (remember - we want the air to be replaced from the house not through an open window, especially during colder months).

Where and how the inline fan unit is positioned can also affect the noise level. Ideally placing the fan unit equidistant between the internal ceiling grille and the external grille will help minimise the noise in the bathroom - placing the unit closer to the bathroom ceiling grille will increase the volume of both the airflow and the unit itself. You can also mount the fan unit on the material to minimise any transference of vibrations through the building itself. A section of underlay or carpet works well, or some rubber foam or even some thick rubber washers between the base of the fan cradle and the screw points can reduce vibrations passing through the building. It’s also worth looking at what is directly below the fan unit - is it over a bedroom? Is it resting on a joist that runs over a bedroom or living space further along? Some of this may be trial and error but with a little bit of forward planning, you can usually save yourself a lot of issues later on.

Below is a simple checklist that may help you with planning and positioning your inline fan installation:


Through-The-Wall Installations

In the second example let’s take a standard through the wall axial fan. There are a lot less variables here that can affect perceived noise. Ideally, these fans should be installed using solid ducting directly through the wall, connecting to an external grille. This will make for the neatest and least fiddly installation and of course, give all the benefits we covered above regarding solid ducting versus flexible. Again, the room replacement airflow is important to allow the fan motor to work at its optimal speed and without additional pressure on the unit. The fan position is always important but with a through-the-wall install there is little effect this position will have on perceived noise.

One area that can have an effect on perceived noise is the choice of external vent and, as mentioned before, this relates to inline and other ducted installations as well. Most external vents these days no longer include a fly screen. These were a piece of mesh that covered the internal aperture of the external grille to stop insects from entering the duct. However, the main issue with the mesh is it would also act as a net for any dust, fluff or debris blown through the ducting by the fan unit. Over time the mesh would build up with this debris causing an obstruction to the air flow and therefore hindering the extraction rate of the unit. Similar to the effect we discussed before when covering the end of a vacuum cleaner, obstructing the air being vented will also cause the fan to over-work which will cause the same additional noise being produced while straining the motor.

We suggest using an external grille that gives minimal resistance and also helps to minimise backdrafts which can also add to the system noise by increasing back pressure for the fan to work against. The No Resist grilles are an excellent solution here for wall mounted extraction points or the Standard Fixed grille is ideal for soffit extraction.

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