Semi-rigid ducting and Plenums - noise considerations when installing

[FlibbleWibble]

Hi,

 

I’m undertaking a self install of an MVHR using 90mm diameter semi-rigid ducting. The duct is not very compliant and needs strap banding a lot to hold it in position as it makes turns. Should I worry about clipping it direct to joists/underside of floorboards because of noise transmission from the rooms above?  Does anyone have any good or bad experiences of how to fix semi rigid ducting and avoid any in-house noise getting into the ducts.

 

Also the same for plenums. These I intend to install tight to the floor above which is how their side clips work but will noise come through them direct and should I consider another approach?

 

thanks,

Flibble

[Conor]

Don't use strap bands, use the proper plastic clips. 

[Nickfromwales]

Noise? There shouldn't be any 'noise' if the unit is fitted according to the application. I oversize if there is any risk of the client requiring "graveyard quiet" and not had a complaint yet (quite the opposite in fact). Acoustic dampening is achieved via attenuators, and vibration / transmission of, is dealt with by never (having to be) running the unit at near full speed.

 

I use strap band and (sorry @Conor) hate the clip bases and monster zip-tie approach, and I've banded to the upper P5 deck (Egger board), to the posi-joists, and everything in-between, and I have not had an issue in the last 8+ years of installing, or being associated with the design & installation of, an MVHR arrangement.

 

MVHR does not, nor should it, make 'noise'. If it does, something has gone very wrong with your design process. 

[Nickfromwales]

Ah, Christ on 2 bikes. I just read your intro.......

 

MVHR into a house which isn't airtight?

 

I don't have much more to say that won't make you look like you've just peeled a very big bag of onions, sorry.

[Kelvin]

I used strap band too. Was very careful to make sure none of the ducting was hanging free but even if it was it’s not going to move or vibrate. My other half was really concerned about the noise of the MVHR system largely because someone was telling her how ‘crap’ they are. I explained it should be more or less silent which it is. We have two large attenuators which are crucial to add. 

[jayc89]

Also a strap bander here. I got some cheap diffusers which are crap and need swapping out, probably for Lindab ones, but otherwise no noise concerns. Only ever hear the system when on boost and that's because our bathroom gets really steamy and I have the system boosting higher than it technically needs to be. 

[JohnMo]

Strap bands here also no issues 2 years in.

 

13 hours ago, Nickfromwales said:

MVHR into a house which isn't airtight?

Seems to be more of this happening, seems like money down the drain now and forever more to me. All the normal ventilation plus a load more by the MVHR, the additional 24/7 running cost plus an additional (small) heating cost due to the unrecovered heat loss.

 

Going this way, get a humidity sensor or two, Shelly H&T are good. Then set the flow rates (keep them balanced) so the house sits at 45 to 50% humidity. Set to auto boost at 60% humidity.

[ProDave]

9 hours ago, Nickfromwales said:

MVHR into a house which isn't airtight?

Surely though if installing mvhr to a non airtight house, you would at least block up all the old original individual vents for the multitude of individual fans, and block up or keep closed the window trickle vents, so you are down to just the leaks in the building fabric rather  than all the previous deliberately made great big holes in the building.

 

And while you are at it block up the letter box and cat flap.

[jayc89]

14 minutes ago, JohnMo said:

Strap bands here also no issues 2 years in.

 

Seems to more of this happening, seems like money down the drain now and forever more to me. All the normal ventilation plus a load more by the MVHR, the additional 24/7 running cost plus an additional (small) heating cost due to the unrecovered heat loss.

 

Going this way, get a humidity sensor or two, Shelly H&T are good. Then set the flow rates (keep them balanced) so the house sits at 45 to 50% humidity. Set to auto boost at 60% humidity.

 

Suppose it depends on the long term goal. When I fitted mine there were still rooms in our house that were leaking like a sieve, I had the ducting for those rooms sitting in the floor void above them ready for when I got to them. The short term consequence was the MVHR was less efficient in the rooms that I had already worked on, but that was acceptable to me. 

 

Totally agree if there's no long term goal to address the airtightness though. 

[FlibbleWibble]

Thanks for all the responses,

 

Looks like I will go with strap banding. 

Yes the unit will have attenuators straight off the bat, my noise concern was about additional noise entering the ducts from sounds transmitted into the ducting through the floorboards/supporting joists.

 

Perhaps I've been misinformed (mis-sold!) but I understood MVHR was OK (albeit not fully effective at heat recovery) in a building built to modern building regs standards (which should achieve <5ach).  The goal here is to have controlled fresh air/extract to all rooms in the house and hopefully retaining some of the warmth of the extracted air.  Maybe this will be false economy over the years but I can't afford passive house standard for the house renovation (only doing a self install of the MVHR not the rest of the build).

 

 

[Conor]

I've a few bags of leftover ducting clips if anybody wants them 🤣

[Kelvin]

48 minutes ago, FlibbleWibble said:

Thanks for all the responses,

 

Looks like I will go with strap banding. 

Yes the unit will have attenuators straight off the bat, my noise concern was about additional noise entering the ducts from sounds transmitted into the ducting through the floorboards/supporting joists.

 

Perhaps I've been misinformed (mis-sold!) but I understood MVHR was OK (albeit not fully effective at heat recovery) in a building built to modern building regs standards (which should achieve <5ach).  The goal here is to have controlled fresh air/extract to all rooms in the house and hopefully retaining some of the warmth of the extracted air.  Maybe this will be false economy over the years but I can't afford passive house standard for the house renovation (only doing a self install of the MVHR not the rest of the build).

 

 

You won’t really gain much/any heat if you’re airtight result is around 5 and it’s questionable whether there is any benefit in fitting it all. 
 

On the passive house point. You really don’t need to build to passive house standards to get 90% of the benefits of a well insulated airtight house with minimal cold bridging. Therefore I’d be aiming to get the airtightness as low as you possibly can. There are people on here who have achieved remarkable air tightness results in renovations. If you’re still at the early stages then revisit your airtightness plans. The better you make it the more beneficial your investment in MVHR will be. You can do the airtightness yourself. The NSBRC in Swindon do courses which are worth it but it’s mostly taking a methodical logical approach to do doing it, using the right materials for the specific task and not allowing the trades to drill random holes around your external walls/roof without considering how best to do it to maintain the airtightness. There is loads of information on here about it too. 

 

 

 

 

 

 

Edited May 4 by Kelvin

[JohnMo]

1 hour ago, FlibbleWibble said:

only doing a self install of the MVHR not the rest of the build

Modern building methods are no better, could be worse than old ones. The normal builder not giving a bit of care or understanding of airtightness. If you have no airtightness strategy you will have a leaky house.  Window installation is a good example, mine were installed and all gaps filled with airtight foam, most installers will fit a trim over the gaps, leave the gaps unfilled to leak air and a cold bridge for mould for form. All holes through the building were drilled a duct installed and sealed in place. Once cables etc were in the foam filled and sealed at both ends. A normal builder would make walk away never to return.

[Nickfromwales]

4 hours ago, Conor said:

I've a few bags of leftover ducting clips if anybody wants them 🤣

At least you took it like a man lol. 

[Nickfromwales]

4 hours ago, FlibbleWibble said:

Thanks for all the responses,

 

Looks like I will go with strap banding. 

Yes the unit will have attenuators straight off the bat, my noise concern was about additional noise entering the ducts from sounds transmitted into the ducting through the floorboards/supporting joists.

 

Perhaps I've been misinformed (mis-sold!) but I understood MVHR was OK (albeit not fully effective at heat recovery) in a building built to modern building regs standards (which should achieve <5ach).  The goal here is to have controlled fresh air/extract to all rooms in the house and hopefully retaining some of the warmth of the extracted air.  Maybe this will be false economy over the years but I can't afford passive house standard for the house renovation (only doing a self install of the MVHR not the rest of the build).

 

 

No need for thanks, and glad you see this feedback as constructive   

In a nutshell, your natural infiltration from having a modern building regs build (apologies, but 🤢🤮) will almost definitely be bean-counted by design, work executed at the minimum deliverable standard (you hope), and holes / gaps etc all left to blow a hoolie through. 
When the natural infiltration rate hugely exceeds the MVHR flow rate (which is tiny in normal operation in an airtight dwelling) you’re stuffed. You’ll be sucking in ice cold air from outside all winter (which will be Baltic during the arse of winter btw) and pumping it into the bedrooms and living spaces. It’s a fact that this will significantly increase your heating demand, as there will be (I fear) the square root of feck all heat recovery with such an install.

 

I talk more people out of these types of retrofits than into them, after, of course, explaining to them WHY. Most salespeople fail to state the cons, naturally, as they need to pay the mortgage etc. 🫤

[MikeSharp01]

7 hours ago, FlibbleWibble said:

Thanks for all the responses,

 

Looks like I will go with strap banding.

We went strap as well but I wrapped the pipe with strips of sponge carpet underlay to be sure I isolated any vibration.