Insulated ducts MVHR

[Oz07]

I have the option keeping MVHR ducts above or below loft space.Trying to decide based on practicalities and headroom. How much insulation do these ducts need over/around them? There will be plenty in the loft so will be well covered but would this be enough? It would be more straightforward to keep them in a small suspended ceiling space below this but I don't want to create a particularly low ceiling and I reckon these will need minimum 150mm void to form a 90 bend?

 

[joe90]

I would not compromise my ceiling height if you have spare loft space, loft insulation is cheap, 200mm laid on top (if insulation exists below them) IMO would be more than adequate. Mine is installed in a warm loft (so no insulation required, apart from incoming from outside to the unit) and it was soooo much easier to instal in an open space.

[Jeremy Harris]

The diagram below is taken directly from the MIs for our Genvex MVHR:

 

 

Together with this text:

 

[Oz07]

Thanks both for replies

 

Would I be right in thinking the ducts to rooms would be 'fresh air and exhaust air' in the note above? The insulation doesn't seem so critical in these so perhaps in the loft with the loft wool layered around seems viable. The main ducts will obviously have a more detailed insulation but these will be relatively short runs.

 

The property is single storey. I'm nailing OSB on underside of trusses to for airtight layer a bit like yours @joe90. Bit of a suspended ceiling below this to prevent plumber and sparks from creating a million holes in OSB. The question i'm considering is to push the MVHR pipes up into loft or increase void and keep in insulated airtight layer. Pros and cons with each I suppose. Probably have to seal up 10 penetrations if have in loft but get away with a smaller void.

 

I'm not particularly limited with overall building height as I had it drawn quite high for planning.

[joe90]

@Oz07 depends where your manifold goes, if it’s in the loft then all “distribution ducts” will need to penetrate your airtight layer anyway and your manifold will also need insulating, this is why having a warm loft was so easy for me. Loads of room to service/install everything. I did see a drawing somewhere (but can’t find it) where the MVHR unit and manifold are installed in a cold loft but in a “box “ and the airtight layer and insulation go over it, so it becomes part of the house rather than loft. Would need a door to access it fir servicing/setting it up but easier than a full warm loft (tho I like mine).

[Oz07]

Unit in service cupboard below airtight layer for easy servicing

 

Would this lend itself to manifold in same cupboard?

 

Would it then impact the decision on where supply vents go?

Edited October 16, 2019 by Oz07

[Jeremy Harris]

43 minutes ago, Oz07 said:

 

Would I be right in thinking the ducts to rooms would be 'fresh air and exhaust air' in the note above? The insulation doesn't seem so critical in these so perhaps in the loft with the loft wool layered around seems viable. The main ducts will obviously have a more detailed insulation but these will be relatively short runs.

 

 

 

In that Genvex note, fresh air and exhaust are the external ducts that run to the terminals outside the house. 

 

Supply and extract are the ducts inside the house leading to the various rooms.

[joe90]

20 minutes ago, Oz07 said:

Unit in service cupboard below airtight layer for easy servicing

 

Would this lend itself to manifold in same cupboard?

 

I would think so. Less penetrations of airtight layer especially if the duct then run in service void.

24 minutes ago, Oz07 said:

Would it then impact the decision on where supply vents go

 

Do you mean the ducts to outside? Fresh air and exhaust as per @JSHarris note above? Where do you plan to put these?, is the cupboard on an external wall?, if so no need to break the airtight ceiling barrier at all.

[NSS]

Doesn't help in the OP's case, but this is another reason why we went for a warm roof as it avoided the need for the MVHR ducting to be insulated (except where the inlet and exhaust enter/leave the building).

[Oz07]

You sure @JSHarris that cutout. Everytime I read it I get a different meaning for those ducts!

 

Unit in cupboard in warm space. Plan was for incoming and external ducts to go straight up through ceiling into roof space then out through roof vent tile.

 

Ducts to rooms to either go via cold loft (but insulated) then back down into rooms

OR

Into ceiling void then into rooms.

 

Whats the tightest bend these ducts can form?

[Jeremy Harris]

4 minutes ago, Oz07 said:

You sure @JSHarris that cutout. Everytime I read it I get a different meaning for those ducts!

 

Unit in cupboard in warm space. Plan was for incoming and external ducts to go straight up through ceiling into roof space then out through roof vent tile.

 

Ducts to rooms to either go via cold loft (but insulated) then back down into rooms

OR

Into ceiling void then into rooms.

 

Whats the tightest bend these ducts can form?

 

 

Yes, as the insulation needed on the externally connected ducts is less than that needed on the internal ducts, when the thing is fitted in a cold loft.