125mm Plastic Ducting - Connecting a new MVHR

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I am installing a new MVHR unit to replace an old failed and undersized unit. The new unit is a Vent Axia Kinetic Advance S .

The house has 125mm plastic ducting, I am having to change some of the ductwork near the MVHR as it is a lot bigger. I have worked out how to do most of the ductwork but a couple of bits don't seem to fit properly.

I am planning to join the ductwork to the MVHR using 127mm Flexi ducting similar to the old stuff but with a thin plastic coating. I did a test to see how the flex fits to the MVHR spigots and it seems very tight. Before I do the final install and tape it up I want to check that I am doing the right thing.

I am also confused by the round connectors on the bottom of the rectangular to round converter thing, the round end does not fit inside standard 125mm round pipe, I have one where I need to connect it to a T connector and then connect the T to the MVHR spigot. What is the corrcet way of connecting to the rectangular to round connectors?
 

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You want to avoid using flexi ducting if at all possible, or just have a very very short length to reduce vibration. I was able to work mine to just have about 50mm on each pipe, and that was a smooth pipe, sold by BPC Ventliation.

What you show on the flat to round adapter seems fine to me, it fits over a solid pipe OK, but not directly onto another fitting. Other than that, if can be differences between manufacturers.

Edit - just seen the last 2 pictures, in that configuration you can't really avoid the flexi pipe. If that garage is unheated, the whole lot needs insulating....
 
You would do better posting this on BuildHub, loads of good MHRV info on there
 
You would do better posting this on BuildHub, loads of good MHRV info on there
Yes they are very good I have posted some stuff there but needed more info duct connections.
 
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You want to avoid using flexi ducting if at all possible, or just have a very very short length to reduce vibration. I was able to work mine to just have about 50mm on each pipe, and that was a smooth pipe, sold by BPC Ventliation.

What you show on the flat to round adapter seems fine to me, it fits over a solid pipe OK, but not directly onto another fitting. Other than that, if can be differences between manufacturers.

Edit - just seen the last 2 pictures, in that configuration you can't really avoid the flexi pipe. If that garage is unheated, the whole lot needs insulating....
Yes I am going to keep the flexi to a minimum, Vent Axia say there should be a short length on each spigot max 150mm, I think mine will be a bit longer but not too much. I know I will have to insulate it, I will probably box most of it and add insulation inside the boxing, I don't know much about this sort of insulation, can I use rockwool or is there something specific needed for ventilation?
 
Any insulator is fine , and if you can pack the whole boxing out with Rockwool , including behind if it's a cold wall (Not too tight of course), then it would be fine.

If you decided to do them separately, they sell a 20mm Rockwool type thing thats foil covered, and very very itchy. I've also been recommended sheets of Armaflex, as being very efficient for the thickness, but of course very edxpensivce too!
 

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