Noisy inline extractor fan

[Feltwell]

Any of you clever bunch know much about extractor fans?

My en-suite previously had a through-the-wall wall mounted extractor fan, that wasn't that good. So, in the refurb, I thought an inline fan with an inlet fitted directly above the shower cubicle would work better. Only problem is, it's quite a convoluted route for the ducting to get to an outside wall.

I used flexible aluminium ducting and it was rather rubbish - the corrugated spirals of the ducting offered too much air resistance and turbulence in use, even with it stretched out. Very quiet but very little air passing through it!

So, I bit the bullet and re-did it all in 4" plastic round ducting and fittings. It's probably only about a 2m run in total, but it's complicated - 3 x 45 degree fittings and 2 x 90 degree fittings have had to be used, plus an anti-backdraft flap on the exhaust. Good news is, airflow has increased dramatically - bad news is, it's now quite noisy.

It's not the fan - that is genuinely very quiet - it seems to be the airflow and acoustics of the ducting. I tried substituting part of the new "solid" ducting for flexible, in case it was vibration transmission from the fan, it made no difference. It's not the inlet in the ceiling, you can pull the cover plate off that to make it just a hole in the ceiling, if anything that makes it louder!

The fan is actually in the ceiling of the room next door, in that room it's pretty quiet - it's the en-suite, where just the inlet is, that has the noise.

Now it's not unbearable by any means, just louder than I'd like. I've turned the fan speed down which does improve matters, not tried it with the shower yet but suspect it may be too much of a compromise.

Any bright ideas? I know you can get insulated flexible conduit, but it's still spiral ridged so I think I'll get the same problem as first time. I will be wrapping some rockwool around my new ducting, just to help stop any condensation.

I suspect it might just be a side effect of my wiggly route that I have to live with, but if any of you lot have any ideas, they'd be gratefully received! The route is as straight as I can make it, with 45 degree bends used in preference to 90's where I can.

 

[Cubist]

What I know about these fans can be typified as sweet fanny adams but..... maybe some ideas: -

Assuming that direct noise from the fans motor is not the root of the problem that then leaves sound created by the air-flow itself or perhaps by vibration transmitted to other components in the ducting system. Presumably the fan motor is quite powerful so I think I would be considering how the various 'hard' turns you have in the plastic ducting may be operating as hard surface baffles that cause significant turbulence. In a closed system significant air turbulence may be one possible root of the problem. Another could be vibration in the body of the pipes, again caused by air turbulence, that in turn creates unwanted noise. Have you considered 'damping' any brackets and fixings of the pipes to isolate the pipes to reduce/eliminate vibration? Would it be possible to 'smooth' the air flow through the hard-turns using shaped baffles? The only other thought that comes to mind is the nature of the physical connection between the fan motors chassis and the ducting.

Sorry Feltwell but thats the best I can offer right now other than a perhaps an unwelcome question - how did you plan to clean the fan assembly and ducting? Peridiodically the darned things will accumulate all sorts of grime that can cause them to make really unpleasent noises, as I've found to my own irritation.

 

[noj]

I was about to suggest wrapping the duct in insulation, but then read to the end of your post!
That might make all the difference.

Once you run the shower then the white noise of the water may cancel it too.

Last thought, sure you won't have, but have you still got an access hatch open into the area with the ducting? I know my fan is a lot louder with the loft hatch open...

 

[CliffordPope]

I have noticed that the noise of the motor itself is greatly affected by what the motor sits on. For example, just sitting on plasterboard makes a loud drumming noise, but lifting it up and sitting it on a pad of insulation greatly quietens it.
I suspect it might be the solid pipework you have used - I think the fan should be isolated from the structure of the shower as well as any joists etc by soft rubber mountings and a length of non-rigid convoluted hose either side.
I've always just used the standard plastic corrugated hose that comes in the kit, resting on insulation and with more insulation piled on top.

I've also noticed that the fan accumulates dust very quickly, which accentuates any noise.

 

[Feltwell]

Thanks everyone for thoughts.

The fan is actually above the to-be-completed false ceiling of the bathroom next door to the en-suite with the inlet. At the moment, it's just sat on 2 bits of wood across 2 ceiling joists - with no ceiling below - despite that it's actually pretty quiet in there.

The support bits of wood will be getting a block of noise absorbing foam glued between them and the joists beneath them - no screws. The fan will then be screwed to those bits of wood. I thought about the fan connection to the ducting - it's just an interference push fit - I tried using flexible conduit to take out any vibrations, it made no difference.

Cleaning the ducting is good point. There will be a loft hatch in the bathroom ceiling to get at the fan unit, I'll make it so that the main part of the duct can be pulled apart if need be. It'll be a bit awkward but hopefully won't need doing very often!

The shower noise does help drown it out, it's just the perfectionist in me would like it quieter!

I think it most likely is just the multiple twists and turns that are required, makes the air a bit "swirly" (getting technical here! ) at the inlet. Baffles in the pipes may be an answer, not sure I'll go to that length though. Hopefully wrapping some insulation around it will help, and give some cushioning for the ducting.

 

[Cubist]

An 'off the wall' thought on this thread occurred to me last night provoked by our bore hole pump kicking in to fill the loft water tanks. Over the years I've become oblivious to the noise produced by 'water hammer' in the pipes up into the loft space. This got me thinking about the possibility that a pressure imbalance may arise in your convoluted ducting as the motor kicks in and this produces a vibration that in turn translates to noise.....

Best ignore me, when unresolved problems like this come along I can be like a dog with a bone...... maybe I should just focus on finding and fixing that hammering pipe.

 

[Feltwell]

An 'off the wall' thought on this thread occurred to me last night provoked by our bore hole pump kicking in to fill the loft water tanks. Over the years I've become oblivious to the noise produced by 'water hammer' in the pipes up into the loft space. This got me thinking about the possibility that a pressure imbalance may arise in your convoluted ducting as the motor kicks in and this produces a vibration that in turn translates to noise.....

Best ignore me, when unresolved problems like this come along I can be like a dog with a bone...... maybe I should just focus on finding and fixing that hammering pipe.

Oooo, it's much more fun to hypothesise on problems that don't directly affect you than resolve the ones that do!

I think we all do that. It's a bit like planning projects and buying the bits required always seems to be easier than physically getting on the project..... Says the man who is fed up with doing the bathroom and has decided to spend the day in the gardem!

 

[CliffordPope]

I've noticed that both water pumps and extractor fans get noisier with age. What they have in common is a fast rotating impeller or fan. The water pump impeller gets corroded - if cavitation becomes acute then the mini-explosions can quite severely dig into the surface. When you think that when new it would have been polished smooth and just cut cleanly through the water, but when roughened through use it gets noisier.

Dust in a damp atmosphere seems to stick stubbornly to the blades of an extractor fan, and periodically needs thorough cleaning with soap and water. It's not like dry dust, which usually simply blows out on tapping the motor and giving a burst of high speed.
I have wondered whether plastic may be specially prone through static build up attracting dust. Perhaps a fan with a metal blade might attract less dust.

 

[LadyArowana]

You need one of these….. Says she who knows precisely zero about, fans and ducting and regards a bathroom as a place of pampering and relaxation. I spent all the money on beautiful Venetian mirrors, nothing left over for drilling through the walls, and anyway I *forgot to put that on the Listed Building Application.

*I didn’t forget, I didn’t want nasty noisy fan

https://www.ductstore.co.uk/acatalog/Bell-Mouths-with-Mesh.html

 

[a twig]

Periodically my fan gets a bit noisy, my slightly odd fix is to hold a sheet of toilet paper up to it so it gets sucked to the grille.

Leave it there for 30 seconds and pull it down again and job done

Presume it is something to do with changing velocities / pressures but seems to “clear” it quite well.

Outside conditions do make a difference though - when we have a North Westerly the fan ends up fighting directly against it and gets a lot noisier

 

[Feltwell]

Now here's an odd one....

I noticed that black spots had appeared on the bathroom ceiling, which looked like mould - which was weird because the room had been well ventilated all thoughout summer, the window was always open, plus it's been family proofed - you can't have a shower now without the fan being on and it runs for about 10 minutes afterwards as well. There had been no real condensation to speak of in there, and there was no mould before it was revamped, when the ventilation was not as good.

Anyway, came to clean the black spots off today, only to find that once I was up close on a step ladder they were actually tiny insects. Quite what made them decide to land and then die and stick to my ceiling I've no idea.

 

[Drayton]

Now here's an odd one....

I noticed that black spots had appeared on the bathroom ceiling, which looked like mould - which was weird because the room had been well ventilated all thoughout summer, the window was always open, plus it's been family proofed - you can't have a shower now without the fan being on and it runs for about 10 minutes afterwards as well. There had been no real condensation to speak of in there, and there was no mould before it was revamped, when the ventilation was not as good.

Anyway, came to clean the black spots off today, only to find that once I was up close on a step ladder they were actually tiny insects. Quite what made them decide to land and then die and stick to my ceiling I've no idea.

I find that small black insects fling themselves onto many of my wet painted surfaces (I try to pick them out asap, pull or sand them out later or, if ithe surface is not going to be seen close up, paint over them . Must be their equivalent of glue sniffing. So might yours have landed while your ceiling was still damp, if you painted it as part of the refurb?

 

[noj]

It would be really useful if fans had a quick release button to remove the impeller. Could then clean it easily and also get a hand in to the clean that bit of the duct.

Mine gets noisy when the dust/gunk buildup on the inside of the duct touches the fan blades

 

[Feltwell]

I find that small black insects fling themselves onto many of my wet painted surfaces (I try to pick them out asap, pull or sand them out later or, if ithe surface is not going to be seen close up, paint over them . Must be their equivalent of glue sniffing. So might yours have landed while your ceiling was still damp, if you painted it as part of the refurb?

I know exactly what you mean and that has happened to me, but no, these little blighters did it 6 months after it was painted!

They really are tiny - 1mm across at most.

 

[malcolm]

Noise and vibration troubleshooting is my day job. What does the noise problem sound like? It's almost certainly going to be air-borne noise if you can hear it in the shower and nowhere else.

If it's a windy noise like then probably turbulence. But I'm guessing you have more of a tonal noise. Or is it a hollow noise?

 

[Feltwell]

Noise and vibration troubleshooting is my day job. What does the noise problem sound like? It's almost certainly going to be air-borne noise if you can hear it in the shower and nowhere else.

If it's a windy noise like then probably turbulence. But I'm guessing you have more of a tonal noise. Or is it a hollow noise?

Windy noise I'd say - turbulence. Makes sense with all the fittings that have had to be used.

Much improved since I turned the fan speed down, and it still seems to clear the steam OK so I may have a fix.