Odd vent size?

[Randomusername]

I’ve got a small MVHR unit to install in the house that I’ll be renting out again next year. 
 

It had 2 vents supplied with it but I’m not sure what tubing I’m meant to use to connect into pipework. 
The concertina foil tube supplied with the system is more or less 100mm as expected, but the vents seem to be made for slightly smaller tube - see images. 

 

The spring clips in the recess suggest that it’s designed so that pipe is pushed into the recess and held in place that way, rather than taped around the outside?

 

Any suggestions please?

[MJNewton]

Surely the spring clips are merely to hold the inner section of the vent up inside the outer? I don't think they are designed to attach to the ducting.

 

What's the inside diameter of your ducting i.e. what's the delta between the 94mm OD of the vent and the ID of the ducting? My vents have have a rubber ring around the outside that fills this cap; perhaps you could fabricate something similar (eg gap-filling foam tape).

[Randomusername]

4 hours ago, MJNewton said:

Surely the spring clips are merely to hold the inner section of the vent up inside the outer? I don't think they are designed to attach to the ducting.

Doh!

?

You’re right about that. 
I’d thought it was a single piece because of how tightly assembled, but it does in fact come apart into 3 pieces. 
I’m still not much clearer though regardless...

 

 

Edited November 20, 2020 by Randomusername

[GreenGuy]

The bottom (last) picture is made of two parts, the part held by your thumb goes through the 100mm hole in the ceiling from the room side. The part below your thumb comes off and is secured above the ceiling by screws going from the room side through the pre drilled holes, through the plasterboard and into pilot holes drilled into the part above the ceiling. The ventilation concertina foil tube is attached to the larger part.

[MJNewton]

I wouldn't expect flexible ducting of that type to be used for runs to ceiling vents? 

[Randomusername]

2 hours ago, MJNewton said:

I wouldn't expect flexible ducting of that type to be used for runs to ceiling vents? 

What type of ducting should be used?

[MJNewton]

Either solid or the somewhat confusing name semi-rigid:

 

Solid:

 

    or 

 

Semi-rigid:

 

 

In all cases the interior is smooth (or relatively smooth in the semi-rigid case) and thus minimises flow restrictions that would otherwise occur with flexible ducting.

 

Edit: I've just re-read that you've got a 'small MVHR' unit... how 'small' is it? I've also just spotted that whilst you've got two vents that's all that's intended on being used? In which case perhaps the 'proper' approach I describing above might not be quite so important and flexible ducting would suffice (like it would with, say, an inline bathroom fan extractor).

 

 

Edited November 20, 2020 by MJNewton

[Randomusername]

2 hours ago, GreenGuy said:

The bottom (last) picture is made of two parts, the part held by your thumb goes through the 100mm hole in the ceiling from the room side. The part below your thumb comes off and is secured above the ceiling by screws going from the room side through the pre drilled holes, through the plasterboard and into pilot holes drilled into the part above the ceiling. The ventilation concertina foil tube is attached to the larger part.

That starts to make sense - I’m still baffled as to what purpose that foam performs - it looks like it’s meant to form a seal, but when pushed into the socket, it does not make contact with the surface of the plasterboard or the flange of the socket. There will always be a gap?

[Randomusername]

4 minutes ago, MJNewton said:

Either solid or the somewhat confusing name semi-rigid:

 

Solid:

 

    or 

 

Semi-rigid:

 

 

In all cases the interior is smooth (or relatively smooth in the semi-rigid case) and thus minimises flow restrictions that would otherwise occur with flexible ducting.

 

 

I’ve got some short lengths of the plastic solid 100mm - can I use a short section as a joiner onto the flexible ducting?

There will only be short runs so I’m not sure that flow restrictions will be too much of a problem?

Edited November 20, 2020 by Randomusername

[MJNewton]

Could the foam be intended to be used to fill the gap between the outer diameter of the upper valve portion and the ducting? (i.e. it's currently sitting in the wrong place)

[Randomusername]

2 minutes ago, MJNewton said:

Could the foam be intended to be used to fill the gap between the outer diameter of the upper valve portion and the ducting? (i.e. it's currently sitting in the wrong place)

I could be wrong but I remember it as being fixed in position there. 

[Randomusername]

@MJNewton it’s going to suck air out through the bathroom ceiling, through a heat exchanger and out the gable wall, in parallel sucking air in, through the heat exchanger and out the landing ceiling next to the bathroom. 
So yes, in lieu of an extractor fan, providing constant trickle input ventilation and extraction, with a boost setting for when steam and vapour is being created. 

[MJNewton]

Perhaps choice of ducting is less critical in that case, and if flexible ducting is acceptable then obviously that flexibility will be to your advantage because it can be clamped down on to the odd-sized vent using a jubilee clip.

Edited November 20, 2020 by MJNewton