Some questions on MVHR installation

[bluebirdnick]

Hello all. 

 

I am in the process of extending our 1930s house* and I am struggling a bit with ordering it from BPC. THey have had  a few goes at  the parts list and they keep making changes, and when I question the changes they keep changing things back without explanation, which makes me worry that they are not going to send me a complete system. I could do with some advice on how these systems actually get installed as it will go a long way to helping me understand what they are proposing. This is not a criticism of BPC who have been super-helpful, but I do want to make sure we get it right first time around! Apologies for the length of this post. I set out first some basic details of the system I need; and then the questions I have which will help me finalise my order. To be clear - these are all questions I have already put to BPC over the last few weeks, but the chap I am speaking to (who is super-helpful generally) has not been able to get me answers to some of these. 

Any advice or comment would be very much appreciated! Thanks. Nick

 

---------------------

Basic facts:

 

- 4-bed, 2 bathroom detached house approx 200m2

- Semi-rigid 75mm radial ducting is now installed. No other kit has been bought yet

- Unit to be installed in the cold loft space above en suite or bathroom. Roof is hipped, so I will stand the unit on the loft floor as wall -mounting is problematic.

- Unit is an airflow BV400, for reasons of cost. 

- We dropped the ceiling in the en suite by a good 200mmm. All of the ducting for the ground floor rooms, with the exception of the living room, runs from ground floor to loft via a stud wall in the en suite. 

- I therefore intend to fit a distribution box for the "extract" ducting  in the space created by the dropped ceiling in the en suite i.e. beneath the main joist and the loft insulation. I think this will make things a lot tidier in the loft space and mean that more of the ducting stays on the warm side of the insulation, and can be sited very close to the MVHR unit. 

- The ducting for the "supply" rooms runs through the cold loft space. Seems easiest to attach the distribution box for the supply side to the underside of the roof rafters somewhere above the MVHR unit itself.

- External supply/intake will be in the side wall of the house, with the galvanised metal ducting run through the space created by the dropped ceiling in the en suite - again on the warm side (although not sure this really matters)

- I know my house is not exactly a prime candidate for MVHR, so I am looking to minimise noise in the bedrooms and living rooms ie on the "supply" side. I want the "extract" side rooms to be quiet but I am less bothered about a small amount of noise in those.

 

--------------------------------------------------

 

Here are my questions - any guidance would be much appreciated!

 

1) The specification initially included rubber connectors, which have not been included on later versions of the parts list. I have asked for rigid drum sound attenuators but they keep specifiying semi-rigid ones instead. As far as I can tell, the semi-rigid attenuators are used to connect from the MVHR unit to the distribution boxes, and are seemingly preferred because it makes installation easier. I cannot work out what the rubber connectors were doing on the parts list but it seems fine to exclude them.  I have however asked why there are no 90 degree bends for the rigid ducting on the parts list but have had no explanation - that is surely an error? Surely I need to at least make one turn as the external vents are on a side wall, and more likely 3 turns? There are also no connectors for the rigid ducting. Again - surely an error? The longest run is about 4m to the external vents. I've questioned it but the parts list still excludes connectors. 

 

2. And how does all of this actually fit together?! This is what I have in mind - corrections of confirmations would be much appreciated, as well as comments on the best option:

 

Connection from MVHR unit to external vents:  

Option a: MVHR unit 160mm terminals --> 160-150mm reducer --> 150mm rigid ducting, including 3x 90 degree bends --> 150mm external vent

Option b: MVHR unit 160mm terminals --> 160mm rigid ducting, including 3x 90 degree bends --> 160-150mm reducer --> 150mm external vent

 

Connection from MVHR to distribution box:

Option a - (simplest): MVHR unit 160mm terminals --> 160-150mm reducer --> 150mm semi-rigid attenuator -- > distribution box 150mm spigot

Option b - (simple too): MVHR unit 160mm terminals --> 160mm semi-rigid attenuator -- > 160-150mm reducer --> distribution box 150mm spigot

Option c - (quietest?): MVHR unit 160mm terminals --> 160-150mm reducer --> 150mm semi-rigid attenuator -- > 150mm drum attenuator --> distribution box 150mm spigot

Option d - (quietest?): MVHR unit 160mm terminals --> 160mm semi-rigid attenuator -- > 160mm drum attenuator --> 160-150mm reducer --> distribution box 150mm spigot

 

3. Is the drum attenuator overkill? On the supply side I have an insulated distribution box, and BPC seem insistent on the semi-rigid attenuator. On the extract side I have a standard distribution box and the semi-rigid attenuator. 

 

4. I keep asking for the dampened room supply valves to minimise noise in bedrooms, but they keep specifying standard PVC. Is there any reason why dampened valves shouldn't be used?

 

5. I have floor to ceiling built-in wardrobes with sliding doors in some bedrooms. Can I install the room valves inside the wardrobes to minimise noise, or will that render them ineffective? 

 

6. Access to the floor void above certain rooms is not possible without significant disruption. Two problematic ones are the WC and the utility. Both had normal extraction fans which extracted to the outside, until we built a two-storey side extension on that side of the the house. can easily poke a duct through the hole that was there for the fan into both rooms. The easier of the two is the utility, which had a wall-mounted extraction fan. We also moved the boiler flu a bit so have a spare hole to play with there too:

 

I plan to use a standard plenum, with the ducts joining to it vertically from above so that the 125mm pipe sticks through one of these holes, and I can then put a standard valve on the other side. I will obviously fill up the rest of the hole so it is secure, and fix the plenum to teh wall somehow.  Does that work? Or do I need a different plenum/valve combo for this?

 

7. The WC is harder. That has a ceiling mounted fan currently, like this:

 

 

And again, I can relatively easily poke a 75mm duct through there to the room itself (you can see the opening tucked in there on the left hand side):

 

 

But how do I fix the plenum if I cannot access the ceiling void? If the answer is "it's impossible" then I may need to block up that window and fit a wall-mounted valve as part of that, lust like in the utility. 

 

7. Quality/costs of items. I cannot see any difference beteween say a standard plenum and a premium plenum. What am I missing, if anything?  Same goes for standard vs premium valves. For the bedrooms I've assumed I would want the airflow dampened valves to minimise noise, but the airy ones are at least double that price. Are they twice as quiet?

 

8. I plan to run the ducting for the downstairs living room through a built-in wardrobe in the bedroom above as I have no other access to the ceiling void without tearing up finished rooms. The wardrobe has a plinth (say 15mm deep). My plan is to run the ducts down vertically and join to a straight plenum, into which I will insert a 350mm extension pipe. I will cut 125mm holes in the wardrobe plinth; the floorboards beneath; and finally the ceiling (lath and plaster, overboarded with plasterboard) and poke the extension pipe through that channel and attach a valve to the underside. Does this make sense or is there a better way to do it? 

[JFDIY]

Think I would phone them up and talk to them, I keep getting emails from them saying they are open for business.

 

Have you sent them plans and asked for a full design. If memory serves thay may be a fee (circa £100) to do a full plan which is then refundable against your future order.

 

 

There are loads of on here that have DIY'd an MVHR design/install and I found you have try and resolve each issue one by one. 

 

 

Just a couple of things I looked into from your post.

 

I wouldn't worry about the room valves for now, get the pipework and room plenums sorted out first.

 

The premium plenums seem to have mounting points built in, the others you will have to hold in place with  strapping band or fashion some mounts to retain them.

 

For the one you don't have access to then you could fix the outlet grill to the plenum then fix the grill to the ceiling.

I have a similar situation, but I used 100mm Flexi pipe for a couple of meters (as per basic individual fan set up) , then connected to the 75mm radial duct, I don't have a restricted terminal vent either so used a restrictor in the manifold to balance flow.

 

The Flexi silencers are regularly used to save on bends and ducting to/from manifolds. If you want rigid silencers then you'll have to use bends and ducts to suit, can't comment on what is best from a noise attenuation point of view.

 

Oh and if the unit is in the cold lift, all the pipes need to be lagged, others have built an insulated enclosure around the whole unit to prevent condensation.

 

[bluebirdnick]

Thank you! I love the idea on fixing the plenum to the valve first - that may well work!

 

As regards calling - I've spoken to them at least half a dozen times, but they don't seem to address my questions on the items on the parts list, they simply remove the ones that I question the need for. But the current parts list has 6 reducers and no bends or joins for the rigid ducting runs, which makes no sense. And they don't seem to acknowledge my requests for dampened valves, drum attenuators etc and I am not getting responses to questions like whether I can put valves in wardrobes. This isn't a criticism - I get the feeling they are working with skeleton staff because they did say that some of their design capability was reduced during lockdown. But lockdown is also something of a golden opportunity to get all of this installed so I do want the kit delivered asap! They really have been good otherwise and I would actually recommend them (as long as we agree on a complete parts list that will work). The lagging is another thing that had been missed - they were specifying 4m of the stuff, and I have four ducts that run at least 10m through the loft space. 

 

I did send them my building control drawings and they did draw up something of a plan for me, but it didn't really work. They had ducts running through RSJs, and were assuming that solid walls were cavity walls capable of carrying ducting from loft to ground floor. I have sent them more detail and photos to show where it is much easier to run ducts but had no revised drawings. I assume they will materialise when I order. 

 

The other thing I have asked for but had no detail on, is how on earth I am supposed to measure airflow for the purposes of balancing the system. The calculations taht I assume they are doing are all well and good, but let's face it they will bear no relation to the actual flows!

 

 

Edited April 28, 2020 by bluebirdnick

[JFDIY]

4 minutes ago, bluebirdnick said:

The other thing I have asked for but had no detail on, is how on earth I am supposed to measure airflow for the purposes of balancing the system.

 

 

You use an anemometer and funnel to read the actual flow. There are a couple in the tool loan pool on this forum, but both now have a bit if a queue for them.

 

I was going to use a road cone and cheap anemometer (£30 on eBay/Amazon), but a proper kit (Testo 417 + funnels) came available and I bought that.

 

 

 

[Bitpipe]

BPC supplied my system, I found their design ok but they compensated by specifying extra duct (rigid and flex) to give me some flexibility on final layout. As their design service is free, I wouldn't expect too much from them vs a supply and install firm (who will charge you handsomely).

 

Some other comments:

 

I wouldn't put the plenums in wardrobes unless they have suitable gaps to maintain airflow.

 

You typically need a 760mm2 gap at the bottom of each door in a room where there is supply or extract to allow the necessary airflow - remember that MVHR systems are barely noticeable when in normal mode and only marginally more so when in boost mode so any obstruction will just impede the air flow in that room and unbalance the system.

 

We must have got the premium plenums (don't remember a choice) and they were very robust with mounting points and easy to use clips to secure the flexi duct. Buy a can of WD40 Silicone spray as that's essential to get duct with a washer deep enough inside the plenum to secure - it is a very snug fit and easy to kink the washer if too much friction.

 

The flex duct still has a reasonable bend radius and it can be a challenge to get lots of connections made to the distribution box in a small space. My system, installed in a new build, took quite a bit of trial and error to get right, especially when many ducts started to congregate through a small opening (my fault for not making provision in the initial building design) but I got there in the end.

 

My install strategy was to position the plenum and then run the duct from near the distribution box to the plenum, trying to minimise sharp bends as much as possible. When all ducts were in place I started offering up the duct to the distribution boxes and carefully trimming to get good connections with out there being too much excess duct pushing against the boxes. A bit of slack is welcome in case you over trim a duct and need to free up another 20mm or so.

 

I didn't have much option on routing the steel duct and had to get creative with the various bends and spacers to navigate them through floor joists etc. Tip there is to work backwards from your external and remember to leave enough space between the duct and wall or in wall / floor penetrations for the lagging (thicker than you think). For complex joints, I secured up the bends and straights with masking tape until I was completely happy, marked up the pipes with sharpies and only then used the bonding compound and silver tape to make the joints final.

 

Balancing was easy enough once I got a loan of the tool  - tbh I did this almost two years after install just to get BC signoff and can't say I really noticed the difference in performance!

[dpmiller]

on the insulation, they supply it on a roll,  you cut it to match the circumference of the pipe. So roughly 2m duct per metre of insulation...

[JFDIY]

I went and cherry picked components from a few places based on quality, cost or location (I.e. I could collect in person)

 

One thing I made extra effort to source was 150mm insulated ducting, I used the ubbink foam ducts as it looked easy to engineer the routes I wanted and no need to insulate separately after installation, can dismantle them for easy cleaning now installed as well.

 

 

There's some pics in this thread.

 

https://forum.buildhub.org.uk/topic/11747-silencer-can-it-be-mounted-horizontally/page/2/?tab=comments#comment-208334

 

Also made a few of my own vertical terminals for about £3 each, but mostly because I couldn't get exactly what I wanted

 

 

 

 

Edited April 28, 2020 by JFDIY

[Cambs]

9 hours ago, bluebirdnick said:

The specification initially included rubber connectors, which have not been included on later versions of the parts list. I have asked for rigid drum sound attenuators but they keep specifiying semi-rigid ones instead. As far as I can tell, the semi-rigid attenuators are used to connect from the MVHR unit to the distribution boxes, and are seemingly preferred because it makes installation easier. I cannot work out what the rubber connectors were doing on the parts list but it seems fine to exclude them.  I have however asked why there are no 90 degree bends for the rigid ducting on the parts list but have had no explanation - that is surely an error? Surely I need to at least make one turn as the external vents are on a side wall, and more likely 3 turns? There are also no connectors for the rigid ducting. Again - surely an error? The longest run is about 4m to the external vents. I've questioned it but the parts list still excludes connectors. 

I’ve spent the last few days fitting my Vent Axia MVHR with the semi rigid ducting, supplied by BPC.  I had the design done by them but it needed to be tweaked when I was doing the install, so it wasn’t perfect by any means.

 

I suspect that what they mean by the “rubber connectors” mentioned are the things that are used to make the final connection between the rigid pvc pipe coming in from / going out to the outside of the building to the spigots on the MVHR unit.  I think they are specified to reduce vibration.  They supplied me with flex ducting instead to cut a small piece to make that final connection.   It has to be kept uncompressed so, I’ll have to support the vertical pvc pipes which drop down in to it.  Have a look at Page 7 of the install guide to see the rubber connectors to the spigot.

 

https://www.bpcventilation.com/mvhr-installation-guide

 

They supplied me with the necessary 90 degree bends and connectors that fitted with their design, so you will definitely need to include them in the parts list. 

 

I’ve got the semi rigid attenuators and they do give you a bit of flexibility in fitting which I found useful

[Roundtuit]

Sorry, don't want to be negative, but your pics look like you've got trickle vents in your windows. If that's the case, I'd have a serious rethink about whether you'll get a benefit from mvhr; there might be better ways to invest the money.  

[bluebirdnick]

15 minutes ago, Roundtuit said:

Sorry, don't want to be negative, but your pics look like you've got trickle vents in your windows. If that's the case, I'd have a serious rethink about whether you'll get a benefit from mvhr; there might be better ways to invest the money.  

Good spot. Yes we have trickle vents in 3 places. The one you can see here (the WC downstairs); the back bedroom; and the kitchen bifolds. The WC window you can see here will be removed and blocked up shortly anyway (we have extended on that side of the house so it opens up into the side extension. And I will seal up the bedroom and kitchen ones when I am fitting the unit.

 

However the general point you make is one I have been grappling with. A 1930s house is far from airtight. We have done a lot to improve things since we bought it, not really with airtightness in mind but nevertheless helpful. For example, I ply-lined the suspended timber floor downstairs, taping joints and refitting skirting boards; replaced all doors and windows; wet plastered every wall, and overboarded and skimmed every ceiling; blocked up chimneys and replaced the roof. We have also extended on two sides (wet plastered walls with the exception of one); and rendered most of the outside walls. But there will still be loads of places for air to move around - I have done nothing about sockets, light fittings, letterboxes etc. So yeah - I accept that to make the HR part work I have quite a bit to do and even then it may be futile, but I still want a system that takes stale, moist air out of wet rooms and puts fresh air back into bedrooms and living rooms. The MV part is more important to me, any HR I get from it is a bonus!

[bluebirdnick]

12 hours ago, JFDIY said:

 

There's some pics in this thread.

 

https://forum.buildhub.org.uk/topic/11747-silencer-can-it-be-mounted-horizontally/page/2/?tab=comments#comment-208334

 

 

 

 

Thank you - that looks brilliant! 

 

 

[Roundtuit]

3 hours ago, bluebirdnick said:

 The MV part is more important to me, any HR I get from it is a bonus!

 

That's my experience, and it seems to be a shared view on the subject. Sounds like you've got the rationale nailed!

From memory, the insulation BPC supply was only to cover the rigid 150mm intake/exhaust duct; runs of duct to rooms can be covered by loft insulation.

[Bitpipe]

I've been meaning to retrofit a silencer on my BPC installation as there is just one supply vent that we get noise from and it would be the one above my bed  Low drone normally but increases noticeably when on boost, especially at night when house is quiet).

 

The flex silencer you detailed above looks like a cheap punt and will be easy to install. Will be ordering one this week!

 

 

[Dreadnaught]

1 minute ago, Bitpipe said:

I've been meaning to retrofit a silencer on my BPC installation as there is just one supply vent that we get noise from and it would be the one above my bed

 

Oh that's interesting. If it is in a bedroom then that would be a supply vent. Do you not have any silencers at all on your install therefore?

 

I am aware of the debate about having a second silencer on the return-side, but yours would be the first install I have come across without any silencers at all. 

[Bitpipe]

1 minute ago, Dreadnaught said:

 

Oh that's interesting. If it is in a bedroom then that would be a supply vent. Do you not have any silencers at all on your install therefore?

 

I am aware of the debate about having a second silencer on the return-side, but yours would be the first install I have come across without any silencers at all. 

 

I decided to wait and see on silencers, never specced any in the original plan. MVHR unit is in basement plant room so plenty of space to retro fit one there - would be on the 160mm fresh supply port of MVHR, not the specific flexi as I probably don't have access to that anymore.

 

Not sure why that port is particularly troublesome - all I can think of is that it's on the same side of the house as the MVHR (wasn't able to centrally locate) so the pipe run is relatively short compared to others. Also, as it's running along roof joists and not pozis, it needed to run laterally in the ceiling void to the eaves and then cut back, so maybe the relatively tight bend at that point is causing an issue.

 

Almost (but not quite) motivated to crawl into the loft eaves to check, but pretty sure I boarded over that bit to enable storage

[bluebirdnick]

13 hours ago, Roundtuit said:

 

That's my experience, and it seems to be a shared view on the subject. Sounds like you've got the rationale nailed!

From memory, the insulation BPC supply was only to cover the rigid 150mm intake/exhaust duct; runs of duct to rooms can be covered by loft insulation.

Thanks. Yes that is what they have told me, but the ducting in the loft runs across rather than along my joists and to be honest I'd rather have them tied up to the rafters anyway. I've upped the spec to include 18m of the foil-backed duct insulation. 

[bluebirdnick]

6 hours ago, Bitpipe said:

 

I decided to wait and see on silencers, never specced any in the original plan. MVHR unit is in basement plant room so plenty of space to retro fit one there - would be on the 160mm fresh supply port of MVHR, not the specific flexi as I probably don't have access to that anymore.

 

Not sure why that port is particularly troublesome - all I can think of is that it's on the same side of the house as the MVHR (wasn't able to centrally locate) so the pipe run is relatively short compared to others. Also, as it's running along roof joists and not pozis, it needed to run laterally in the ceiling void to the eaves and then cut back, so maybe the relatively tight bend at that point is causing an issue.

 

Almost (but not quite) motivated to crawl into the loft eaves to check, but pretty sure I boarded over that bit to enable storage

Interesting. Is the theory that the shorter the pipe run, the greater the noise in the room? I'd be interested in the experience of others in attempts to minimise noise. As far as I can tell there are a number of components that are designed in part to reduce noise:

 

1) the unit itself which presumably is the origin of any noise 

2) the rubber connectors for connecting the unit to the ducting to the outside, presumbly to minimise the transfer of unit noise to the ducts and therefore the area above the living space below?

3) rigid drum sound attenuators, whose only purpose seems to be to reduce noise

4) semi-rigid attenuators, which seem to have a dual purpose of reducing noise and simplifying installation of the distribution boxes

5) the distribution boxes themselves - some of them come fitted with 20mm insulation. Clearly sound attenuation is a secondary purpose.

6) the foam dampers/silencers which you can insert into the plenum and even stack in series. These seem to have a dual role of reducing noise and controlling airflow

7) the valve - some have sound dampening built-in, presumably similar to the foam damper

 

How many of these do people actually install on each leg? Most (all?) of the insallations I have seen have the semi-rigid flexible attenuator to connect to the distribution box and many have the druma attenuators. But how many use the foam dampers, or sound attenuating room valves? And has anyone retro-fitted any of these items so have a feel for how effective any one component is? My proposed system has an old, cheap unit and they don't make rubber connectors to fit it, so that is item 1 and 2 I've failed on. I do intend to fit items 3 and 4 on both supply and extract sides, and an insulated distribution box on the supply side. I have no idea whether I need the foam dampers or how many it takes to make any difference (they can be installed in series), but I do intend to fit dampened valves in all bedrooms and living rooms. But this is all guesswork really on my part, and I wonder if this is all overkill or whether the law of diminishing returns kicks in at some point and that I will simply have to make do with a certain level of noise.

[JFDIY]

Just to add to your dilemmas, if you throttle the airflow at the room terminal you will find that as you close them down (on rooms closest to the unit) the noise increases.

 

Its been said that if you throttle the flow at the manifold the noise created is less noticeable. Some suppliers sell knock out restrictors for this purpose.

 

 

 

[bluebirdnick]

10 minutes ago, JFDIY said:

Just to add to your dilemmas, if you throttle the airflow at the room terminal you will find that as you close them down (on rooms closest to the unit) the noise increases.

 

Its been said that if you throttle the flow at the manifold the noise created is less noticeable. Some suppliers sell knock out restrictors for this purpose.

 

 

 

I had assumed that I would have to adjust the flow at the room valve, or use one of those foam inserts, which I thought was designed to reduce noise, not create it!? How do I throttle it at the distribution box? My head hurts!

 

This is a problem for me - the main bedroom is the closest bedroom to the unit, by a good distance. And it is the one room where I want absolutely no noise! My wife is already doubtful as to the merits of this system and has threatened to turn it off if she can hear it at night. Hmm!

Edited April 29, 2020 by bluebirdnick

[bluebirdnick]

Thanks to everyone who has commented so far- it is really helpful.

 

On the subject of noise: my unit has 160mm connectors. Because BPC don't stock 160mm ducting and therefore don't have many items that would fit 160mm, I have been assuming that I would have to step down to 150mm at the unit. But I've had a look, and I can get 160mm ducting, attenuators, distribution boxes and wall vents from other suppliers. My thinking is that the wider pipe would carry 14% more air than the smaller pipe at the same fan speed, thus reducing fan speed and so hopefully reducing noise. But even if this logic holds up, is the difference just too trivial to matter, and am I obsessing over something that in reality will make no difference to performance or sound? On the one hand I am really reluctant to split the order and just get everything from BPC And stick with 150mm and reducers. But on the other hand, in addition to my thoughts on fan speeds above, I am drawn to the neatness of everything being the same diameter! (plus the other supplier's gear has rubber seals which I think would de-skill installation; they can cut the duct to length for me... and it is £100 cheaper).

 

 

Edited April 30, 2020 by bluebirdnick

[Dreadnaught]

6 minutes ago, bluebirdnick said:

I am really reluctant to split the order and just get everything from BPC

 

What is it that you can only get from BPC and not the other supplier? Can't the other supplier supply everything you need? What's the advantage of not splitting an order?

 

I'd personally go for 160mm if you have the chance and the runs will fit. All else being equal, bigger ducting will perform better.

[bluebirdnick]

11 minutes ago, Dreadnaught said:

 

What is it that you can only get from BPC and not the other supplier? Can't the other supplier supply everything you need? What's the advantage of not splitting an order?

 

I'd personally go for 160mm if you have the chance and the runs will fit. All else being equal, bigger ducting will perform better.

Thanks. They don't sell MVHR units, plenums, distribution boxes etc. They specialise in metal ductwork. I've also found another supplier that can supply insulated distribution boxes with a 160mm spigot, so between the two of them I've got everything I need for a 160mm setup. 

Edited April 30, 2020 by bluebirdnick

[Bitpipe]

13 hours ago, bluebirdnick said:

Interesting. Is the theory that the shorter the pipe run, the greater the noise in the room? I'd be interested in the experience of others in attempts to minimise noise. As far as I can tell there are a number of components that are designed in part to reduce noise:

 

1) the unit itself which presumably is the origin of any noise 

2) the rubber connectors for connecting the unit to the ducting to the outside, presumbly to minimise the transfer of unit noise to the ducts and therefore the area above the living space below?

3) rigid drum sound attenuators, whose only purpose seems to be to reduce noise

4) semi-rigid attenuators, which seem to have a dual purpose of reducing noise and simplifying installation of the distribution boxes

5) the distribution boxes themselves - some of them come fitted with 20mm insulation. Clearly sound attenuation is a secondary purpose.

6) the foam dampers/silencers which you can insert into the plenum and even stack in series. These seem to have a dual role of reducing noise and controlling airflow

7) the valve - some have sound dampening built-in, presumably similar to the foam damper

 

How many of these do people actually install on each leg? Most (all?) of the insallations I have seen have the semi-rigid flexible attenuator to connect to the distribution box and many have the druma attenuators. But how many use the foam dampers, or sound attenuating room valves? And has anyone retro-fitted any of these items so have a feel for how effective any one component is? My proposed system has an old, cheap unit and they don't make rubber connectors to fit it, so that is item 1 and 2 I've failed on. I do intend to fit items 3 and 4 on both supply and extract sides, and an insulated distribution box on the supply side. I have no idea whether I need the foam dampers or how many it takes to make any difference (they can be installed in series), but I do intend to fit dampened valves in all bedrooms and living rooms. But this is all guesswork really on my part, and I wonder if this is all overkill or whether the law of diminishing returns kicks in at some point and that I will simply have to make do with a certain level of noise.

 

No idea on what causes noise but in that room, as the duct is shorter the vent is not very open to balance the airflow. My system is quite lopsided as the MVHR is in the basement plant room on one side of the house, our bedroom is two floors directly above that but we have rooms at the far end of the house with considerably longer duct runs. Made it fun to balance but I got there in the end.

 

Really interested that you found the 'in plenum' foam reducers, they may be an even cheaper place to start for me so I've pinged BPC to get one.

 

My unit mounted to a 300mm thick RC wall so no sound transference there but I have no other sound reducing elements and I only have a hum in that one vent.

[bluebirdnick]

Here is the link. I could only find this by using the search tool - I couldn't find it from their menu system. Same goes for the small plastic clips that hold semi-rigid ducting - once you know they sell them you can search for them but they don't seem to include them in the spec, and its not obvious where they sit in the menu system.  

 

https://www.bpcventilation.com/foam-flow-control-damper

Plenty of advice on on how to install them too. Someone above has suggested (I think!) that these create noise if installed at the valve end, but not at the manifold end. Presumably you use a 125mm insert at the plenum end and shove it in the plastic pipe that pokes through the ceiling; and a 125/150/160/200 one and shove it in the metal/plastic rigid ducting that feeds the distribution box if you are doing it at the manifold end. 

 

I've decided not to order them and see how I get on for now - after all, I've got semi-rigid attenuation; drum silencers; an insulated distribution box and valves with dampers included! If that lot doesn't do the trick I'm not sure how much of an impact the foam insert will have, so I am leaving it for now and will use as a last resort if neccessary. 

[tanneja]

bluebirdnick, as the owner of a 1930s myself, did you replace any of the joists on between the ground and first floor, perhaps with ijoists, so to allow the extract and supply ducts to reach your downstairs rooms?  It sounds like you have a stud wall / void where they travel down, and so presumably shoot out to various rooms within the ceiling.  I Imagine you had to cross past some joists to get to everywhere?

 

If you did replace any joists (with either posi or ijoists), were they taller, and so meaning you had to drop[ the ground floor ceiling slightly?