Insulating MVHR

[AliG]

Hi,

 

I spotted an opportunity to save money a while back and in areas where we are not using the space all the way to the roof I changed from PIR insulation between the rafters to rockwool above the ceiling.

 

What I did not realise though was that the MVHR ducting has to be in an insulated space.

 

So now we need to insulate the MCHR which loses almost the entire saving.

 

The installers have recommended using 50mm foil backed insulation wrapped around the ducts.

 

This is fine, but I wondered if in areas where the ducts are installed just above the roof trusses and the loft insulation was pushed under the duct work could be just add another layer of rockwool that covers the duct work? This would be a lot faster and cheaper, but there is more risk that bits of the duct aren't covered.

[ragg987]

Ideally the insulation keeps moisture out else you will get condensation, which leads to soggy insulation (best case) or structural damage due to moisture if left too long.

 

I had to insulate my ducts 4 times before I got it right. The first 3 were foil-backed insulation wrapped around the duct and sealed with aluminium tape. I thought this would be watertight, but after a few months the condenstion became visible. Does not help that the ducts in question were in our utility room where humidity can rise as we have a clothes line in there.

 

In the end i used Armaflex - no issues since.

[Jeremy Harris]

My experience was very like @ragg987 I'm afraid.  I insulated the exhaust duct from our MVHR using foil backed rockwool and had the same problem with condensation making it get very soggy, even though I taped it up pretty well.  It's now got amaflex over it, with the foil backed wrap stuff over that, as a bit of extra insulation and it seems fine.  Mind you, my problem was caused primarily because the MVHR exhaust from our unit can be below zero when the internal heat pump is warming the incoming air up a bit.

[AliG]

Thanks, my main issue is insulating the service ductwork.

 

After looking at the costs, the 50mm duct insulation is not that expensive.

 

Hopefully we won't have issues on the exhaust duct as we don't have an ASHP getting the air so cold. But it is not too big a job to add armaflex to the exhuast.

 

What caught me out was a very high cost quote from the MVHR supplier for the insulation. They were almost 2x the price I can buy it for.

[j_s]

Are we talking 150mm exhaust duct? If so I can't see solid duct insulation that big.

 

Im slightly worries now my exhaust and intake ducts aren't insulated well enough if you guys had to redo yours. Mine is in the loft and double wrapped with foil backed Rockwool but I'm doubting it's good enough now. It's not on yet but will be soon.

[Jeremy Harris]

2 hours ago, j_s said:

Are we talking 150mm exhaust duct? If so I can't see solid duct insulation that big.

 

Im slightly worries now my exhaust and intake ducts aren't insulated well enough if you guys had to redo yours. Mine is in the loft and double wrapped with foil backed Rockwool but I'm doubting it's good enough now. It's not on yet but will be soon.

 

Sorry, I think I may have caused some undue concern!  Our MVHR has an internal air to air heat pump, so can warm the incoming cold air a bit.  As a consequence, the exhaust air can be down around zero deg C, perhaps even a bit lower at times, so that significantly increases the condensation risk around the outside of that duct.  This isn't a problem if you just have a passive MVHR, with no internal heat pump.

[ragg987]

@j_s my issues were on the supply duct more than on the exhaust - after heat exchange the exhaust tends to be around 8 or 9C, wheres supply can be below 0.

[j_s]

Ok thanks all, I'll look to improve it anyway and make sure the tape is more than good enough and may even triple wrap the intake and look to extend the celotex as far as I can from the main unit to anything close by 

[Stones]

In our last house, we had an Exhaust Air Heat Pump, which exhausted air at -8C, and that certainly was enough to cause condensation problems on the exhaust duct, which was initially flexi duct with the rockwool sleeve insulation.  That issue was solved by replacing it with rigid ductowrk and insulation.  All of the other ductwork in that house was under the earthwool insulation in a cold roof space, without issue. 

 

In our current house, the ducts run under the earthwool insulation in the cold loft and are uninsulated within the heated envelope.  No issues whatsoever.

[Diablo]

3 hours ago, AliG said:

Thanks, my main issue is insulating the service ductwork.

 

After looking at the costs, the 50mm duct insulation is not that expensive.

 

Hopefully we won't have issues on the exhaust duct as we don't have an ASHP getting the air so cold. But it is not too big a job to add armaflex to the exhuast.

 

What caught me out was a very high cost quote from the MVHR supplier for the insulation. They were almost 2x the price I can buy it for.

 

We have 75MM Airflex service ducts running to the rooms. We have Knauf loft roll between the joists, the MVHR pipes sit on the joists and we have the second layer going over the top of the pipes. So, the pipes are sandwiched between the two layers of loft roll.  This is exactly how Airflex recommended it should be done, and it works fine for us.

[PeterW]

Are we talking the main supply ducts to the units or the radial ducts to the rooms here ..??

 

For supply ducts you can buy nitrile rubber insulation in sheets to cut to size. Doesn’t take much and it can be quickly and easily done,  use EvoStik solvent glue on the joints and do it in two layers. If you can’t either InsulTube or Armaflex sheet in small quantities then you can just using camping roll mats but they need to be covered with something non-flammable. 

[tanneja]

@Stones and others, if you don't mind clarifying for me, I had intended have a Vent Axia unit in my cold loft, and have the room duct runs snake around the cold loft, then going down to 1st floor and ground floor rooms.  What type of insulation should I provision for that 75mm duct work?  If a generous layer of Rockwool, would you then have to board over the top to avoid crushing one accidentally when going up to service the filters?

 

p.s. I have see the attached images of the installation advice from one company and hopeful my builder would think covering the 'room to MVHR' sets of ducts in this way, without any gaps (in the pictures akin to laying a blanked over protruding duck work), would be doable.  Frankly, it has to be doable, given the design decisions I have made already:

 

I assume the foil backed glass fibre insulation that comes with the BCP kits was used for the main extract / intake pipes?  I have seen references made to encasing the MVHR unit in PIR sheets, still allowing for condensate drain to function, and ability to get to the filters.  Would encasing in PIR like this be advisable?  Presumably summer overheating is a potential issue.

Edited August 24, 2020 by tanneja

[Stones]

@tanneja - hello.  If you lay your ductwork within the earthwool layers (as per the 1st image) then you shouldn't have any problems - this is how ours is laid.  If you have to clamber over multiple ducts to get to your unit, then I would suggest you think urgently about relocating your unit so it's easy to get to from / beside your loft hatch/access. If you can't do that, I would suggest a boarded walk / crawl way to get to the unit so you don't have to disturb the insulation / risk damaging a duct.  

 

The foil backed fibre insulation supplied is indeed intended to wrap the main intake and exhaust ducts.

 

We initially had our unit in the cold loft, just next to loft access hatch.  I housed the unit in a PIR shed to keep it 'warm', the front being removable to allow access for servicing.  The condensate drain was connected.  This still proved a bit of a hassle and earlier this year I relocated the unit into a cupboard within the heated envelope.  This had been the original intended location so all my ductwork was geared to doing this in any case.  Much easier now.

 

 

[tanneja]

Thank you @Stones, I sincerely appreciate your assistance.  I will likely be getting the Kinetic Plus B which I think you have had at one time or another.  Your post on servicing yours has been pinned to my favs and will be very helpful I am sure when the time comes.

 

I haven't managed to find posts where you describe any maintenance schedule for the ducts them selves, would you mind saying if you attempt to clean these somehow (either the external connecting or just the internal servicing sets).

 

Again I offer my thanks

[Thorfun]

if I may jump in on this thread and ask my own question?

 

I have a friend who is about 3 months ahead of us with their self-build. they've had their MVHR installed and the ducts all run inside the insulated envelope, yet I noticed that the installers insulated all the supply ducts to the rooms.

 

I assume that's because they have a 'cooling' element to their MVHR system?

 

we are planning to plan for the possibility of using a fan coil/duct cooler fed from the ASHP to potentially add a cooling element to the MVHR if we require it a couple of years down the line. so I assume that I'd need to also insulate ALL the supply ducts to every room in case we do go down the cooling route? but if we don't need a cooling element with the MVHR then insulating supply ducts when inside the insulated envelope of the building is not necessary?

[joth]

4 hours ago, Thorfun said:

we are planning to plan for the possibility of using a fan coil/duct cooler fed from the ASHP

 

I think fan coil units will need their own dedicated (insulated) ducting and outlets to recirculate air around at a higher rate. Duct cooler is normal for MVHR pipes and means the supply ducts need insulation as you say. 

Did you have a specific fan coil unit in mind? I literally might buy mine in Italy and get couriered over, they're so hard to source here

 

PS planning to plan is exactly how I roll too ?

[Thorfun]

3 minutes ago, joth said:

 

I think fan coil units will need their own dedicated (insulated) ducting and outlets to recirculate air around at a higher rate. Duct cooler is normal for MVHR pipes and means the supply ducts need insulation as you say. 

Did you have a specific fan coil unit in mind? I literally might buy mine in Italy and get couriered over, they're so hard to source here

 

PS planning to plan is exactly how I roll too ?

thanks @joth. I have no specific units in mind for anything yet! still on the research stage. 

 

I'm tempted to run pipework to multiple locations and just cap it off and then when I decide if/how to cool then I can pick the best place to do that based on the unused pipework in place. eg. I could put an AC unit (or fan coil I guess) in the loft and run a duct to the vaulted entrance hall like @Jeremy Harris suggests he'd have done it. or I could run a duct cooler with the MVHR in the plant room. so I might as well insulate the supply ducts and run a few copper pipes to a couple of locations....all just in case! 

 

still have loads of research to do on this and many other subjects! 

 

I look forward to reading about your exploits in this area.

[joth]

This is the supplier I'm looking at:

https://www.shopclima.it/en/panasonic-paw-fc-d15-r-aquarea-compact-fan-coil-with-right-side-connection-1-5-kw.html

 

€214.00

 

Plus €75 shipping (it does reduce if I order multiple, so a bulk buy maybe an option although the UK wide onward shipping might wipe out the benefit)

@ProDave also interested in this topic

[tanneja]

I have been discussing the placement of the MVHR unit with my builder.  We have a potential space on the first floor inside the thermal envelope of the house.  It would be easier to access the filters this way, but there may be more noise (it would be between two bathrooms, so not right next to a bedroom, but less sound insulation than we planned).  Builder thinks pipework would be more of an ask like this.  It would also sacrifice some of the size of one of the bathrooms.

 

Is bringing the unit into the thermal envelope a good idea to try reduce the risk of the unit getting roasting hot in summer, and so even with summer bypass perhaps delivering very warm air via the ducting?  P.S. we have grey roof tiles.

[AliG]

We have three MVHR units, despite my request one is in a plant room and two are in the loft. One takes about 2 minutes to change the filters, one takes about 20 minutes of faffing about with ladders etc and one cannot be changed and needs to be moved.

 

I wish I had really insisted they put them somewhere easy to get at.

 

One unit is in the loft directly above our bedroom, I have never heard it running. Any kind of enclosure at all such as suggested and you will not hear the actual unit.

[tanneja]

47 minutes ago, AliG said:

We have three MVHR units, despite my request one is in a plant room and two are in the loft. One takes about 2 minutes to change the filters, one takes about 20 minutes of faffing about with ladders etc and one cannot be changed and needs to be moved.

 

I wish I had really insisted they put them somewhere easy to get at.

 

One unit is in the loft directly above our bedroom, I have never heard it running. Any kind of enclosure at all such as suggested and you will not hear the actual unit.

Thank you AliG, to confirm, is your loft warm or cold? Beyond convenience, i am wondering if placing in our cold loft puts me at risk of, during a heat wave, it pumping out super heated loft temp air due to being in my cold loft (with grey roof tiles).

 

Perhaps during those heat wave conditions i would switch off the MVHR during the day and instead have an ashp in cooling mode via a multisplit managing the climate, then running MVHR overnight to address the air quality, although doubt the loft will cool that quickly after sundown.

 

I still dont want faff, but since it loses a precious but of bathroom, wanting to determine if there are additional advantages to locating the unit inside.

[MJNewton]

11 hours ago, tanneja said:

Is bringing the unit into the thermal envelope a good idea to try reduce the risk of the unit getting roasting hot in summer, and so even with summer bypass perhaps delivering very warm air via the ducting?  P.S. we have grey roof tiles.

 

I had the same concerns but needn't have worried.

 

Our MVHR unit is in an uninsulated loft and we have temperature sensors inside every port on the unit and one in the loft itself. 

 

I've seen the loft temperature rise to 40-45c with no obvious effect on the supply air temperature. Note that on the hottest of days the unit will likely *not* activate the summer bypass as the outside air is often hotter than that being extracted hence keeping the heat exchanger 'in circuit' can cool the incoming air (heat transfer always occurs hot-to-cold regardless of direction). In such scanarios I've seen a degree or two drop. It's not air conditioning, but it has reassured me that the loft temperature hasn't been an issue. 

 

I wouldn't expect an MVHR unit to overheat in a loft as the heat-generating items are the fans and they sit within the air flow. 

Edited August 27, 2020 by MJNewton

[AliG]

The areas of loft that the MVHR is in are cold. The MVHR units have their own insulation, you can see the polystyrene when you open them up.

 

The external air doesn't spend a lot of time inside the actual MVHR unit on its way through so I don't think it would make any difference. I certainly haven't noticed it. The issue is that the outside air isn't usually that much colder and they don't move enough air to have a serious cooling impact in bypass mode. TBH opening a window will have a much bigger effect if it is that warm. That is where your multi split will come in.

Edited August 27, 2020 by AliG