Bathrom extractor fan - inline vs centrifugal??

[Tony Carrigan]

Hello

I need a new bathroom extractor fan and I'm wondering whether to get an inline axial fan or a centrifugal one so looking for a bit of advice...

Bathroom is internal (no windows) and currently has a fairly cheap ceiling-mounted axial fan (Greenwood Airvac EL100) that isn't really working. I think the main reason for that is because the ducting run is very long - about 8.5m with two 90-degree bends (over the ceiling, down to the floor thru a boxed-in wall cavity, under the floor of the adjacent room and then finally out the exterior wall of the house. The long run under the floor is a plastic pipe but the rest I think is 4" flexible ducting, the usual concertina-like stuff). I read somewhere that a 90-degree bend adds about the same amount of friction as a metre of straight ducting, if true that would make our ducting add up to 10.5m in total. The spec sheet for the Greenwood fan says it's suitable for up to 2.5m of ducting. Extraction rate is 96 cubic metres/hour or 26 litres/sec.

Just looking at what's on offer, I can see there are inline axial fans and centrifugal ones that offer more than double the extraction rate of our current one, for £100-£200
E.g. this Vent-Axia one

Vent-Axia ACM100 4

Vent Axia's ACM100 has long been regarded as the industry standard for inline fans. Vent Axia's superb build quality marries very high extraction rates with extremely low noise levels. Indeed the ACM100 is the quietest inline fan available. The ACM utilizes a 'mixed-flow' impeller, allowing it...

www.airconcentre.co.uk

or this centrifugal one

Vent-Axia Centrif Duo Plus Extractor Fan With Timer - 431614

Features: Easy Installation Fan can be wall or ceiling mounted Suitable for both kitchen and utility rooms Constant trickle boost speed available on DP & HTP models Colour: White

www.airconcentre.co.uk

It's an old Victorian house with 10ft ceilings and the bathroom has a false ceiling about 8ft high, so I think there should be plenty of space for an inline axial fan. But I've noticed people making blanket statements about centrifugal fans being generally better without really explaining why? Are they quieter, more reliable, less expensive to run?

Thanks

 

[Tony Carrigan]

Sorry I should have made it clear that when I said the current fan isn't working, I mean it is working but just doesn't seem to be extracting air. When I do the "toilet paper test" (hold a sheet of toilet paper up to it) the toilet paper doesn't stick. Also the bathroom has a problem with mould (which is the real reason I'm looking to replace the fan).

 

[opps]

I cannot offer any meaningful advice...but I want you to be aware that for an extractor to function efficiently, you need air that comes in (to the room) and can then be extracted.

Fitting an extractor fan is futile is the door (for example) doesn't have a vent that allows non-moist air in to the room and up through the extractor

 

[flameport]

Axial fans are only of use in situations with no or very short ducts, such as directly through a wall.
Centrifugal have much higher pressure and are the only choice for longer lengths of duct.
There are also 'mixed flow' which attempt to combine aspects of both.

Whether it's inline or not is unrelated, that just refers to how it's mounted - inline with a duct, or some other arrangement such as wall/ceiling mounted.

With 8.5m of ducting, there will be problems with all of them.

 

[brig001]

I had a similar situation and fitted one of these

Airflow iCON 30 Low Profile Extractor Fan - White | Aidelle_Airflow (72687257)

You will probably need a timer module too, so not the cheapest option. Works great in our flat with 8m of 100mm rigid duct and a flexi bit at each end. Needs a 150mm hole in the ceiling though

Brian

 

[Taylortwocities]

I had a similar situation and fitted one of these

Airflow iCON 30 Low Profile Extractor Fan - White | Aidelle_Airflow (72687257)

You will probably need a timer module too, so not the cheapest option. Works great in our flat with 8m of 100mm rigid duct and a flexi bit at each end. Needs a 150mm hole in the ceiling though

Brian

The Icon 30 does need a larger hole,
actually when flush fitted:
Hole Size - 160mm - To accept motor body Then 110mm for ducting

but the iCON 15 uses a 4" hole. Lower extract rate though./..

Airflow iCON 15 ECO Low Profile Extractor Fan - 67 m³/hr | Aidelle_Airflow (72683501)

 

[opps]

I had a similar situation and fitted one of these

Airflow iCON 30 Low Profile Extractor Fan - White | Aidelle_Airflow (72687257)

You will probably need a timer module too, so not the cheapest option. Works great in our flat with 8m of 100mm rigid duct and a flexi bit at each end. Needs a 150mm hole in the ceiling though

Brian

I too have the icon 30- with the humidistat/PIR module.

Mine is wall mounted. It is very noisy though. That said, the extraction rate is so impressive that if the door is slightly ajar, it will pull the door closed.

 

[Murdochcat]

Have you checked the air flow under the door?

With bare feet you should feel a decent flow over them?

If the flow isn’t enough no fan will work properly

 

[Tony Carrigan]

I cannot offer any meaningful advice...but I want you to be aware that for an extractor to function efficiently, you need air that comes in (to the room) and can then be extracted.

Fitting an extractor fan is futile is the door (for example) doesn't have a vent that allows non-moist air in to the room and up through the extractor

I think you've made a good point - there is no vent in the door. However - after someone has a shower we leave the door wide open with the fan running for maybe 20mins or so. Even in that situation (door wide open) the fan doesn't seem to be doing anything. I've just gone back in and tried the "toilet paper test" again (with door wide open) and it's not sticking...
So, it seems to me that the fan is the limiting factor at the moment - I need a more powerful fan but will also need to add a ventilation grille or similar to the door for it to work properly when someone is actually in the shower (door closed)...?
(Thanks for your help)

 

[Murdochcat]

^^ have you checked the vent outlet ?

 

[blup]

My vent axxia acm 100 lasted about 3/4 years and was reasonably quiet and efficient at extraction. I added an isolator to turn off the fan when using the b/room at night. The other acm lasted a fair bit longer but was used less. I'm getting a cheap manrose from amazon next as the VA prices have shot up and I'm not convinced they are any better value, especially as I will swap them over myself.

Blup

 

[Tony Carrigan]

^^ have you checked the vent outlet ?

Yes, the external outlet isn't blocked. I've tried checking the ducting for blockages by feeding a length of electric flex through but couldn't get it all the way thru because of the two 90-degree bends. Shone a torch in from the external wall side and could see it's clear at least as far as the end of the straight 5-metre section.
Tried getting someone to direct a hairdryer into the ducting from the bathroom end and could detect a faint breeze coming out the external side.
So I'm reasonably confident there isn't a blockage somewhere but can't say 100%
Cheers

 

[ebee]

I will ditto what Flameport said.
Also the more powerful the fan (in Wattage, in cost, in running costs) should add benefit.
You really need to get some air thru and vent it to outside not into a wall cavity as some do (Yes believe it).
The larger the diameter of the vent, shorter length and less bends all reduce friction - it`s no good having a super strong fan meeting an impossible amount of friction resistance, leaving the door open is a good way to reduce friction so well done on that aspect.

Another aspect is the place the fan is mounted, if the input of air (example the door) and the output of air (the fan) are placed so as to draw the air over much of the bathroom is a good thing.
If the intake and output of the fan "short circuit" then much useful ventilation will be lost - In this case short circuit does not mean an electrical short circuit but a shorth circuit of air flow over a portion of the bathroom - intake and output positions are usually a bit of a compromise but the more you can glean from say moving the fan to suit for example will only help. Obviously moving the door would be a major job unless you are having some structural works done.

A look on say the Vent Axia or Expelair Websites etc should offer some points to consider.

 

[Deryck Tintagel]

I have been looking at a new fan for the bathroom with about 4m duct run to the soffit at the back of the house. I have a ceiling mounted Greenwood that does very little to help so I was looking at inline. One thing I found when reading up was that ceiling / wall mounted axial fans are only good for abot 1~ 1.5m of duct.

 

[Taylortwocities]

I have been looking at a new fan for the bathroom with about 4m duct run to the soffit at the back of the house. I have a ceiling mounted Greenwood that does very little to help so I was looking at inline. One thing I found when reading up was that ceiling / wall mounted axial fans are only good for abot 1~ 1.5m of duct.

Some are so poor that they have trouble pushing through the depth of a cavity wall!