New MVHR install, but have sound issues? Any ideas on a solution?

[LeeV]

Hi,

I have just powered up my newly installed MVHR system, a Vent Axia Sentinel Kinetic, 2 x 6 way manifolds and 50 metres of 90 mm semi rigid plastic ducting. It's a retrofit into the existing loft space.

It seems to be working fine apart from the noise.

Standing under the vents I can hear a gentle 'woosh' of the air coming out of the vents, but from even further away, I can hear what I'd call maybe a 'droning' noise, it's like there is an echoing in the ducting. Not sure how to describe it better. It's not massively loud, but loud enough to raise complaints from the family.

As it's a cold loft, the Sentinel Kinetic has had a 25mm EPS foam box built around it, so it's sitting on a platform, with an EPS base. The same as the metal manifolds, these have 25mm EPS outer boxes too. The ducts are strapped to the top of the trusses. The whole lot has been covered with 400mm of new rockwall insulation.

 

Any insight into where the noise is coming from and how to fix it are greatly appreciated.

[jfb]

Do you have a sound attenuator on the supply side (extract as well)?

this is what is needed to reduce the sound from the vents. I made my own for my first project and that worked very well. Basically an osb box with sound rockwool batts  on the inside (with batts sticking out into the middle to disrupt the airflow - large enough to allow enough airflow). Second project I bought an attenuator (just cylinder with sound absorption ) and it hasn’t been as good as the one I made.

I didn’t have a problem with noise from the machine itself - most of the noise was coming through the vents.

[Redbeard]

Sorry, this is not a response to the noise issue, but can I make a suggestion re the insulation? If the MVHR unit is in a cold loft I would suggest that 25mm EPS is insufficient for its 'shed'. Better than nothing at all, definitely, but I think I'd go for significantly more.

 

Actually, while writing that a thought came re attenuators further to @jfb's comment. Think motorcycle or car silencer if you DIY and don't want to do it with OSB. Offcuts of different -diameter galv ducting, drill-bits, thin sheet steel and HSS drill-bits (and the rockwool mentioned)  could fit the bill.

[saveasteading]

Firstly, how is the box supported? Are there attenuation pads between it and the joists (or whatever supports it). 

Even then,  there are screws which may carry the noise through.

 

Secondly, the pipes are ideal for carrying sound around the house.

Jfb has it right. Ideally the manufacturer would include this or have it as an option.

A plenum ( bigger air space) next to the fan would probably be enough to kill noise. Sound will bounce off the pipes, but if you break the shape,  it will become random and disappear. A baffle might also help, as sound isn't good at getting around corners ; Unless they are smooth pipe corners that is.

It would be essential to make the box and junctions  completely airtight.

@jfb what size was your box and how did you form the junctions?

[LeeV]

@Redbeard Well, the Vent Axia unit is also insulated, but I was thinking another 25mm coat, or maybe two would be pretty simple to add. Especially as I have several sheets of the stuff already in the garage. You've convinced me, a job for next weekend!

 

 As for the attenuator, I didn't install any, as I'd read they weren't necessarily needed. Of course, perhaps I should have tested the system before wrapping the ducts and burying everything in rockwool. What an idiot...

 

@saveasteading the main unit is on a wooden platform above the loft insulation. It's sitting on 25mm of EPS foam, there are metal L brackets to stop it moving but they are screwed into the platform and only touch the EPS  foam wall covering the unit. The two x six way manifolds are the same but sit on boards screwed into the trusses.  The manifolds are 150mm in from the top and a 90 degree bend and 6 x 90mm inlets/outs go out the side of the box. I did put an inch of acoustic foam into the bottom of each manifold (I read that on here somewhere) but even with a 90 degree bend and the foam, it's clearly not helping.  

 

I'm not sure I have the willpower left after the install to built an attenuator, so looking on BPC's site, is this the kind of thing we're talking about ?

 

https://www.bpcventilation.com/quiet-vent-semi-flexible-silencer-range

 

Or maybe a large insulated plastic airtight crate as a plenum?

 

And if so, where exactly would it go? In the duct between the unit and the manifold going to the rooms? Or between the unit and both manifolds?

Or on the fresh air intake from outside? Or even all three?

 

Or would this https://www.bpcventilation.com/attenuator-silencer  be any better?  I guess this is what @jfb bought and @Redbeard built?

 

[crispy_wafer]

is this a DIY install or did you commission a company to do for you?  have you much scope in your airflow calcs to lower the fan speeds?

[saveasteading]

Or your brain will soon filter it out, if you let it.

When it twigged that distant road noise was like distant waterfall sound, it stopped mattering so much. What does your air system sound like?

[LeeV]

@crispy_wafer it's a DIY install, there's plenty of scope to lower it to zero! 

The calcs suggested a fan speed of 42%, which is what it's at, from everything I've read (on this forum too), this is probably too fast, but without running it for a while it's difficult to tell.

 

@saveasteading I don't mind the air whooshing sound, but the echo-y droning reminds me more of being on cross channel ferries more than anything else. While that was OK as a kid, it's not so good now.

 

I've attached at rather poor video which doesn't really do it justice, but you can hear the drone at the start of the video. Obviously there is hum from the mic and it's much louder than in real life as the phone was quite near the vent, but you get the idea.

[saveasteading]

An adjustable fan! Sorted. They tend to have speeds where they thrum. Play with it.

[jfb]

2 hours ago, saveasteading said:

what size was your box and how did you form the junctions?

From memory about 800mm long by 300mm by 400mm . This is with 150mm eps semi rigid ducting. Think I used the plastic connectors that are used with the eps ducting and taped them to the osb.

[jfb]

32 minutes ago, LeeV said:

The calcs suggested a fan speed of 42%

Definitely try at a lower speed and see what works. Is there no controller/switch for different speeds?

 

[Nickfromwales]

You can get down to much lower speeds overnight. Possibly on a timer which diverts to a second controller.

One very good 'box' attenuator may sort this, and I have NEVER installed an MVHR system without either 500mm long ones or 1000mm where I thought the job would benefit / there could be any chance of this type of issue.

[Nickfromwales]

 

Those silver boxes are the box attenuators. Magical bits of kit which help to dissipate any residual sound from the unit. You can see 2x in that pic, but I actually added a 3rd to ensure no sound (during boost) got to the neighbours earholes either.

Forget the flexi duct type attenuators, and certainly do not put rockwool into this scenario as I would not want to convey the strands into the air that you breathe (America and others have banned exposed rockwool), and go with these instead. Try one on the supply air first and see what benefit you get, and only add others as you need to. Maybe just 1x 1000mm long one on the supply air plus 1x 500mm on the extract will do the job.

Do you have the same issue in rooms which extract? 

[LeeV]

4 hours ago, jfb said:

Is there no controller/switch for different speeds?

Yes, it's got a screen/buttons where you can set up the parameters it runs with. I'll give it go turning the speed down a bit tomorrow.

 

3 hours ago, Nickfromwales said:

One very good 'box' attenuator may sort this

Can you recommend one, in case the speed adjustment fails?

 

[Nickfromwales]

9 hours ago, LeeV said:

Can you recommend one, in case the speed adjustment fails?

Speak to CVC Systems directly and they’ll sort you out with whatever ventilation products you need.

 

I buy all of the systems I install for my self build clients through them.
Great guys, and great service / products. 

[LeeV]

After scratching my head for a while about which attenuator to buy, and looking at the DIY versions on this very forum, it stuck me that a "Rapid Cardboard Prototype" was needed to test if an attenuator would actually fix the problem before spending any money on something that may not work.

Which lead to the abomination below. It was just as well I built it out of cardboard, as when I tried to install it, the slope of the roof meant I couldn't actually connect the ducting from the Vent-Axia. Ten minutes, a stanley knife and more tape later, I'd move the input port to the back of the box and it fitted great.

 

And for a cardboard box full of filter material, it works surprisingly well. In the main bedroom, you can't hear the drone from the supply vent, but now the howl from the extract vent in the ensuite is really noticeable!  This is great!

 

So due the headroom constraint, it seems like I have to build a box attenuator. I'm just unsure of the details.

 

Out of 10mm ply? Does the inside need painting? With what?

Presumably bigger is better (I'm constrained by a nearby truss and the roof slope)

Insulated with 50mm of EPS foam on the outside?

 

Fibreglass mat internally seems to be a thing with commercial boxes, but I used filter material as its what I had to hand, and I don't fancy fibreglass strands being pumped into the house. I did thing of lining the box first with the fireproof acoustic foam matting I put inside the manifolds, but that didn't seem to do much there?

 

Then building a copy for the extract manifold? 

Which leaves the question, won't the mat inside the extract manifold box just get soaking wet after cooking/showers as mist/water droplets hit the filter material? Then leading to mould in the box? Or is this not an issue?

 

 

[m0deller]

when it gets cold and humid air hits that box ... probs won't last long ! 

[Post and beam]

I see that the silver attenuators are used in addition to the Ubbink manifolds. I guess that this means the manifolds do not perform the same job.

As i am intending to use Brink/ Ubbink soon this is interesting and useful.

[LeeV]

On 22/06/2023 at 21:55, m0deller said:

when it gets cold and humid air hits that box ... probs won't last long ! 

Definitely! The cardboard was only a prototype to see if it fixes the problem. Which it mostly did. I'm going to replace it with a box built from EPS Foam. Light, thick, fairly cheap and already insulated!

 

On 22/06/2023 at 22:24, Post and beam said:

I guess that this means the manifolds do not perform the same job.

No, they don't seem to. I was rather hoping they would too. Especially after I'd added fireproof acoustic foam to the inside of them! But no... 

[Blooda]

On 28/05/2023 at 21:45, Nickfromwales said:

You can get down to much lower speeds overnight. Possibly on a timer which diverts to a second controller.

One very good 'box' attenuator may sort this, and I have NEVER installed an MVHR system without either 500mm long ones or 1000mm where I thought the job would benefit / there could be any chance of this type of issue.

The sentinel has  "low supply" settings that can be programmed for overnight. 

[Dave Jones]

On 24/07/2023 at 17:49, LeeV said:

Definitely! The cardboard was only a prototype to see if it fixes the problem. Which it mostly did. I'm going to replace it with a box built from EPS Foam. Light, thick, fairly cheap and already insulated!

 

No, they don't seem to. I was rather hoping they would too. Especially after I'd added fireproof acoustic foam to the inside of them! But no... 

 

sure you want to be breathing in plastic particles ?

[lorrianemark]

On 28/05/2023 at 21:55, Nickfromwales said:

 

Those silver boxes are the box attenuators. Magical bits of kit which help to dissipate any residual sound from the unit. You can see 2x in that pic, but I actually added a 3rd to ensure no sound (during boost) got to the neighbours earholes either.

Forget the flexi duct type attenuators, and certainly do not put rockwool into this scenario as I would not want to convey the strands into the air that you breathe (America and others have banned exposed rockwool), and go with these instead. Try one on the supply air first and see what benefit you get, and only add others as you need to. Maybe just 1x 1000mm long one on the supply air plus 1x 500mm on the extract will do the job.

Do you have the same issue in rooms which extract? 

Hi, I'm having issues with noise. I upped fan speed and house felt much fresher but I introduced  noise. Do them box attenuators slip on over intake/extract pipework. Not great at DIY so looking for simple solution. Thanks

[lorrianemark]

Basically is there something b we can put around intake duct to dampen noise. I don't want to remove any ducting that's in place.

[saveasteading]

1 minute ago, lorrianemark said:

something b we can put around intake

Fibre glass stuffed in around it. Or in roll form to wrap around it 

[lorrianemark]

Cheers might try in roll form wrap.