MVHR insulated ductwork throughout??

[matt-me]

Hi there, first post on this forum and a relative newcomer to MVHR although I do have a basic understanding. I understand the importance of using insulated ductwork for the air intake and exhaust ducts to external air. I am building a single storey new build house, approx 120m2 ground floor area with a loft/mezzanine area over most of the ground floor out of 220mm SIPS panels, walls and roof. The MVHR unit will be sited in the loft/mezzanine space which is not heated as such but it is not a cold attic space. Question : is it recommended to use insulated ductwork in this space to run from the mvhr unit to the ceiling valves? I will be running it on the floor around the edge of the loft space, dropping into the posi joisted floor to the rooms below. I will be boxing it in for the most part so could insulated with rockwool or the like. Insulated ductwork adds a fair amount of cost, is it necessary? Is there a real risk of condensation in the ducts that i need to be concerned about? Ideally I would use insulated ductwork but semi rigid ductwork does save a fair bit of cost. Thanks in advance 

[IanR]

Hi @matt-me, and welcome.

 

Are you using a PIR/PUR or an EPS SIP? and do you know the effective U value of your SIP Roof Panels, once the timber fraction is taken into consideration?

 

 

I suspect once the timber fraction is taken into consideration, the U value of the roof panels will mean that your unheated loft area will be cooler than the rest of you house (except under sun loading on a sunny day). Since the hot moist air from a shower-room at say 24°C with 85% humidity has a dew point of 21.3°C it would be advisable to insulate the extract ducts. 

 

Unless you are considering adding cooling to the supply air, there's no reason to insulate the supply ducting.

 

 

 

[matt-me]

Hi IanR. Thanks for this response, very helpful. I was wondering if we should use insulated ductwork for the extract and will take this on board. We are using EPS SIP panels and will try get the effective U value of these. 

[Iceverge]

From how I read it you have a SIP roof as the below pic shows?

 

 

 

 

      COLD LOFT                      WARM LOFT

 

This means you have have a "WARM LOFT"??

 

In this case all the ducting will be inside the "thermal envelope" and even if you have no radiators up there and will be fine without insulation. 

 

 

 

 

 

 

[matt-me]

Hi Iceverge

 

Thanks for the reply. Yes that's exactly what I will be having. I'm in contact now with a supplier who will be designing a scheme and will ask for their thoughts on this too. I'm thinking where I am proposing to run the ducts, the lowest triangle of space next to the eaves, I will be building a small skeiling wall anyway so can insulate them with rockwool or such like anyway. thanks again

[Iceverge]

There's not really any benefit to the insulation in this situation. 

 

Time might be better spent ensuring that the joint between the sips is airtight and insulated or making sure the inlet and exhaust ducts from the MVHR units are insulated. 

 

[matt-me]

That's all on my hit list, thanks