MVHR drone

[JohnMo]

I've had good service from duct store 

[Nick Laslett]

1 hour ago, JohnMo said:

I've had good service from duct store 

 @S2D2, I bought all my spiral ducting form the Duct Store, like @JohnMo.

 

https://www.ductstore.co.uk/acatalog/Attenuators.html
 

They have attenuators. 
 

I used the Lindab Safe Click system, which has rubber gaskets. I bought all these components direct from Lindab. Just find the nearest sales office to you. 
 

https://www.lindab.co.uk/Products/ventilation/Sound-attenuation/?sort=popularity&display=16&page=1

 

They have a huge choice of attenuators. 
 

If you want to be confident that you are going to cut most of the MVHR unit sounds before they hit the manifold, you need an attenuator that is 1000mm long. If you look at the spec sheet for the Lindab Attenuator, the difference between 500mm and 1000mm is significant. 
 

A semi-flexible radial system will also help mitigate the noise. Also, you don’t want your individual ducts going to a supply outlet being too short. 

 

Here is a photo from one of @Nickfromwales installs showing 500mm attenuators, foam insulated ducts and a Ubbink manifold. 
 

Edited October 7 by Nick Laslett

[Nickfromwales]

2 hours ago, Nick Laslett said:

 @S2D2, I bought all my spiral ducting form the Duct Store, like @JohnMo.

 

https://www.ductstore.co.uk/acatalog/Attenuators.html
 

They have attenuators. 
 

I used the Lindab Safe Click system, which has rubber gaskets. I bought all these components direct from Lindab. Just find the nearest sales office to you. 
 

https://www.lindab.co.uk/Products/ventilation/Sound-attenuation/?sort=popularity&display=16&page=1

 

They have a huge choice of attenuators. 
 

If you want to be confident that you are going to cut most of the MVHR unit sounds before they hit the manifold, you need an attenuator that is 1000mm long. If you look at the spec sheet for the Lindab Attenuator, the difference between 500mm and 1000mm is significant. 
 

A semi-flexible radial system will also help mitigate the noise. Also, you don’t want your individual ducts going to a supply outlet being too short. 

 

Here is a photo from one of @Nickfromwales installs showing 500mm attenuators, foam insulated ducts and a Ubbink manifold. 
 

I added a 3rd attenuator to that job, as the client wanted “graveyard in Gravenhill” levels of shhhhh! at night.

 

Then foam duct defo helps out, but I’m now being ‘directed’ towards spiral galv rigid ducting against my will…..

 

I’ll do one and see if it passes muster, if not I’ll be reverting back to foam. 

[Jolo]

I also experienced a droning noise, but after buying a rectangular attenuator from Lindab (thanks to your photos and advice here @Nick Laslett and @Nickfromwales!) which didn't stop it, I determined that it wasn't coming from the main unit, but was being generated within the green ribbed Ubbink Air Excellent ducting.

 

So for the bedroom I added a 1m flexible attenuator at the end, just before the vent, and it works great. To avoid adding too much more static pressure I went for one with a 100mm internal diameter (larger than the 75mm internal diameter of the ducting). It works really well, even on boost it's barely audible and at night we don't have it that high anyway, so it's totally silent.

 

I since added another to one of the living room vents, and it's worked great there too.

 

While this does work, is there anything I'm missing? Is there a reason I've never seen this recommended anywhere? 

[Mike]

8 hours ago, Jolo said:

Is there a reason I've never seen this recommended anywhere? 

Because it's cheaper to centralize the attenuators, rather than installing them per-room. And noise generated within the duct would normally be due to excess air velocity, which shouldn't happen - but you seem to have found an exception :)

[JohnMo]

8 hours ago, Jolo said:

at night we don't have it that high anyway

If at night you can turn down the MVHR aren't you actually running too high in general. There should be zero reason to change base rate at different times of the day.

 

Get a simple co2 monitor and move about at different times of the day. And actually look at what is occurring and tune the flow based on actual needs.

 

I am using Ubbink duct, no noise. You have either under installed ducts based on your flow rates or you are flowing to high a rate.

[Jolo]

On 16/10/2025 at 23:23, JohnMo said:

If at night you can turn down the MVHR aren't you actually running too high in general. There should be zero reason to change base rate at different times of the day.

 

Get a simple co2 monitor and move about at different times of the day. And actually look at what is occurring and tune the flow based on actual needs.

 

I am using Ubbink duct, no noise. You have either under installed ducts based on your flow rates or you are flowing to high a rate.

 

Except when cooking/showering/toiletting, we generally keep it on the lowest setting which right now is 80m3/h. Our house is 200m3, so I think that 80m3/h might be a little higher than most people on here seem to have theirs set (I read a lot that people set the normal rate to 0.3ach, which for us would be 65m3/h).

 

I think it's a bit higher because when we set it up in the summer, the house was stuffier and warmer, so wanted as much night-air bypass ventilation as we could. 

 

I've actually added a strange thing but one which I'm really happy with -- a night-time boost lever for the bedroom. It's a three-way valve which we can move so that overnight the bedroom gets air that would normally be going to the (empty) living room, doubling the output without increasing the fan speed. So this might mean that we can turn the normal speed down to 65m3/h.

 

We do definitely need to get a CO2 monitor, this has been on my list for ages! (Right now we're dealing with a floor that's been bodged, the DIY is never done, even when you hire professionals...)

[JohnMo]

3 hours ago, Jolo said:

Our house is 200m3, so I think that 80m3/h might be a little higher than most people on here seem to have theirs set (I read a lot that people set the normal rate to 0.3ach, which for us would be 65m3/h).

We are similar sized I have mine down to 0.3ACH, almost never have to boost for anything. It just 24/7 at the same rate. In summer we have windows open when we fancy (bedroom is window open all summer). Lounge will go high co2 but only if we have about 8 to 10 people in there. Again I will open the window, as it starts to get hot in there anyway.

 

Your 3 way valve will actively encourage more more noise as the flow rates increase locally. So may be not the best solution for noise.

[Jolo]

I should add for clarity, it was always silent in the bedroom on the lowest setting -- the audible hum was when turning it up in the summer, when we wanted to do to get as much cool night air in as possible, i.e. bypass mode on with no heat recovery. Adding the attenuator before the vent meant that we could increase the speed without adding any noise.

 

14 hours ago, JohnMo said:

Your 3 way valve will actively encourage more more noise as the flow rates increase locally. So may be not the best solution for noise.

I did wonder about that too, although the valve itself is 125mm internally, so although it adds a couple of extra bends, the speed within it should be fairly low. It doesn't seem to have added any extra noise, anyway. Even running on higher settings it's silent in the bedroom (even on boost it's only just audible) which was my main goal.

 

With the 3-way valve set to "bedroom boost" we get about 40m3/h into the bedroom (which I think is what PH guidelines suggest), while the system remains set on the lowest speed.

[Mattg4321]

On 16/10/2025 at 13:20, Jolo said:

I also experienced a droning noise, but after buying a rectangular attenuator from Lindab (thanks to your photos and advice here @Nick Laslett and @Nickfromwales!) which didn't stop it, I determined that it wasn't coming from the main unit, but was being generated within the green ribbed Ubbink Air Excellent ducting.

 

So for the bedroom I added a 1m flexible attenuator at the end, just before the vent, and it works great. To avoid adding too much more static pressure I went for one with a 100mm internal diameter (larger than the 75mm internal diameter of the ducting). It works really well, even on boost it's barely audible and at night we don't have it that high anyway, so it's totally silent.

 

I since added another to one of the living room vents, and it's worked great there too.

 

While this does work, is there anything I'm missing? Is there a reason I've never seen this recommended anywhere? 

Which flexible attenuator did you use on the ductwork to bedroom? How did you adapt it onto the semi rigid ducting? I have a double run to the bedroom

[Mattg4321]

An update to this. 
 

I tried lining the manifold with acoustic eggbox foam, on all sides. It made absolutely zero difference. 
 

I’ve noticed that running the unit at different speeds makes no difference. It just changes the pitch of the droning noise slightly. The unit is only set at 20% anyway as that’s all that’s needed to meet the airflow in the various guidelines. Turning it down to the minimum 15% the unit can operate out doesn’t improve matters. 
 

I’ve also noticed that the noise is significantly worse in bed 1 and the dining room/kitchen supply terminals.  The only 2 rooms where there is currently a double run of 75mm ducting from the manifold (and roughly double the airflow). These are also the 2 longest runs! The other 3 bedrooms are just about acceptable, whereas bed 1 in particular definitely isn’t. 
 

I noticed that in certain areas of bed 1 and with your head turned a certain way, you can’t hear the noise. Unfortunately my pillow does not fall into that category! The terminal is located past the foot of the bed and to the side, so it seems to be a normal position for it. 
 

If I close the terminal completely in bed 1, it stops the noise, so it can’t be noise transmission through anything other than the ductwork from the unit itself imo. It’s not the terminal making the noise either because it still makes it even when it’s removed and the ceiling plenum visible. 
 

I’m going to have to look at fitting a proper silencer (not the useless semi flexible one I currently have). It’s doing to be pretty awkward, but I think doable if it’s 5-600mm in length. Diameter is not really restricted.
 

Any suggestion on all the above? Which specific silencers at that length are best? I’ve looked at Lindab, but they only seem to do 160mm - slightly annoying as my ductwork is 150mm! Thanks. 

Edited 14 hours ago by Mattg4321

[dpmiller]

what about foam lining the plenum? Trying some of the foam flow adjusters is worth a try tho- air can do some pretty wierd things in a tube and slightly increasing or decreasing the pressure might help...

[Mattg4321]

I’m 99% sure it’s noise from the unit though. If foam lining the manifold did absolutely nothing, then I doubt lining the plenum will?

[Mike]

Since silencers attenuate the sound differently at different frequencies it would be worth sampling the noise with an audio spectrum analyser, so that you can compare that with the spec of silencers you consider.

 

I only looked at attenuators that used foam to avoid the risk of blowing mineral / glass fibre through the ducting. I think the only one available in the UK is the Zehnder CSI, which comes in 700mm long for 150 diameter (Brink, Westaflex and Vasco were also on the shortlist):

 

 

 

[Mattg4321]

If I had any idea how to get hold of or use an audio spectrum analyser…!!

 

Are there any iPhone apps any good?

[Mike]

35 minutes ago, Mattg4321 said:

Are there any iPhone apps any good?

There are for Android, so I'm sure there must be iPhone versions :)

[Nick Laslett]

On 05/10/2025 at 22:49, Nick Laslett said:

You can get an audio tools app for your iPhone/iPad, which will tell you the frequency you are trying to reduce. There maybe some free ones, but this is the one I recommend. 
 

https://apps.apple.com/gb/app/audiotools-db-sound-audio/id325307477

 

They have a video on their site demonstrating the FFT function. 
 

https://studiosixdigital.com/audiotools-modules-2/acoustic-analysis-modules/fft/

@Mattg4321, I did link to the iPad/iphone spectrum analysis tool I use earlier in this thread. 

Edited 11 hours ago by Nick Laslett

[Mike]

42 minutes ago, Mattg4321 said:

audio spectrum analyser

BTW, to illustrate why it's useful, compare the frequency attenuation of the Zehnder CSI (above) with this one for the Zehnder silenced manifold that I mentioned on the previous page:

The silenced manifold beats the dedicated silencer at frequencies of 63, 125, 4000 & 8000 Hz.

[Mattg4321]

1 hour ago, Nick Laslett said:

@Mattg4321, I did link to the iPad/iphone spectrum analysis tool I use earlier in this thread. 

Not sure how I missed that. I just downloaded it, but not sure what I’m doing. The 1st picture is with phone microphone a few mm below the centre of the terminal in bed 1. The 2nd picture is the same test in bed 2. Obviously the results are jumping around a bit - possibly as I’m not that still!

 

Only a snapshot in time, but it does appear that bed 1 is slightly more weighted to the lower frequencies than bed 2 for whatever reason. 
 

unit currently on 30% as someone in the bath!

 

 

Edited 10 hours ago by Mattg4321

[Mattg4321]

1 hour ago, Mike said:

BTW, to illustrate why it's useful, compare the frequency attenuation of the Zehnder CSI (above) with this one for the Zehnder silenced manifold that I mentioned on the previous page:

The silenced manifold beats the dedicated silencer at frequencies of 63, 125, 4000 & 8000 Hz.

Are those results for both used in conjunction with eachother?

[Mike]

48 minutes ago, Mattg4321 said:

The 1st picture is with phone microphone a few mm below the centre of the terminal in bed 1. The 2nd picture is the same test in bed 2.

Very useful results. So it is the lower end of the frequency range causing the problem. If I were choosing only between the 2 Zehnder options, I'd choose the silenced manifold.

 

BTW, results would normally measured at 1m distance from the source of the noise (ceiling terminal in your case), so the chances are that the 14dB reduction provided by the silenced manifold at 250Hz would be enough, even if your chart suggests that you have 42.5dB of 250Hz noise a few mm away from the Bedroom 2 terminal. You could measure again at 1m to give help decide.

 

 

23 minutes ago, Mattg4321 said:

Are those results for both used in conjunction with each other?

No - that is for the manifold only. It helps to know that the manifold is modular - that is you can fit different 'end plates' to it depending on what you want to connect. The results in the table above are measured for the following:

• a connector plate for 1 x DN160 or 180 or 200 duct on one end (the first part in yellow)
• a connector plate with 10 x 75 or 90mm semi-rigid duct connectors on the other (the second part in yellow)
• the CW-S520 is the main body of the manifold (not in yellow). Note that there is a regular manifold body too, without the sound attenuation - the 'S' indicates that it's a silencer version.

You would want a connector plate for a 150mm duct (Zehnder 990323568, by the look of it), which isn't one of the ones they used in the test, but the size is so similar to the ones that they did use that performance would undoubtedly be similar / identical.

 

[Mattg4321]

3 minutes ago, Mike said:

Very useful results. So it is the lower end of the frequency range causing the problem. If I were choosing only between the 2 Zehnder options, I'd choose the silenced manifold.

 

BTW, results would normally measured at 1m distance from the source of the noise (ceiling terminal in your case), so the chances are that the 14dB reduction provided by the silenced manifold at 250Hz would be enough, even if your chart suggests that you have 42.5dB of 250Hz noise a few mm away from the Bedroom 2 terminal. You could measure again at 1m to give help decide.

 

 

No - that is for the manifold only. It helps to know that the manifold is modular - that is you can fit different 'end plates' to it depending on what you want to connect. The results in the table above are measured for the following:

• a connector plate for 1 x DN160 or 180 or 200 duct on one end (the first part in yellow)
• a connector plate with 10 x 75 or 90mm semi-rigid duct connectors on the other (the second part in yellow)
• the CW-S520 is the main body of the manifold (not in yellow). Note that there is a regular manifold body too, without the sound attenuation - the 'S' indicates that it's a silencer version.

You would want a connector plate for a 150mm duct (Zehnder 990323568, by the look of it), which isn't one of the ones they used in the test, but the size is so similar to the ones that they did use that performance would undoubtedly be similar / identical.

 

Thanks. I’ll look into it. I’m about to go away for a week so nothing much will be done until after that. 

 

This is the reading from 1m away from bed 1 terminal. 
 

 

[Mattg4321]

That Zehnder manifold looks like it costs over £500 with all the necessary parts!!!!

 

Think I’ll look into a few more options first!

[Nickfromwales]

7 minutes ago, Mattg4321 said:

That Zehnder manifold looks like it costs over £500 with all the necessary parts!!!!

 

Think I’ll look into a few more options first!

Just fitted 2 of these, but they're expensive, yes, but very good build quality; both acoustically and thermally insulated so no need to insulate externally which is a wonderful thing when you're working in the worlds smallest / most awkward plant space!

[Mike]

Just now, Mattg4321 said:

That Zehnder manifold looks like it costs over £500 with all the necessary parts!!!!

Zehnder aren't cheap, but that looks like list price. It should be possible to knock at least 30% off that.

 

The supplier I used (in Germany but delivery to France, not sure if they'll deliver to the UK post-Brexit) are currently offering the main body at a 43% discount (€205 including VAT).

 

You also only need  one unit to silence 10 terminals.