Distance to combustibles flue passing through wall

[jimseng]

Hello.

I have had a flue designed and I now have all the bits on site. The issue is the installer is now not available for some time and I really want to fit the flue through the wall to the outside before the insulation goes in. I haven't been able to get hold of the installer so I thought I would ask here. I have a timber frame building with 350mm Warmcell insulation. The installer has specified 2 45 degree bends and twin wall flue to pass through the bedroom wall to the outside of the house and then up. This means passing through plasterboard, intello membrane, Warmcell then through larch wood cladding. I have been supplied an expandable wall sleeve to surround the twin wall flue where it passes through the wall:

 

This wall sleeve is barely wider internally to the twin wall flue which specifies a 50mm minimum distance to combustibles so I am confused as to how I maintain the minimum distance, unless I have mis-understood, or been supplied the wrong thing. Can someone advise? I'm trying to get all parts that pass through the wall installed before I seal up for the insulation.

[ProDave]

When I did mine, I used an insulated sleeve, supplied by the flue supplier for the purpose.  It was 50mm thick and obviously fireproof and thus everything else gets the 50mm from combustibles it needs.

 

[JohnMo]

 

8 minutes ago, jimseng said:

This means passing through plasterboard, intello membrane, Warmcell then through larch wood cladding

So you need to cut all this back. I would get a suitably rated neoprene flashing/ grommet to tape to your membrane that will get you airtightness back. You may need to add a metal trim plate to get the plasterboard tidy. The insulation around the flue replace with Rockwool as it's classed as fireproof. Warmcell has a fire rating of around E/F, Rockwool is A1. So you may need to box this part of wall in to keep the insulation from mixing.

 

 

[jimseng]

@ProDave. That looks like the sort of thing. Do you have a supply reference for that? I assume, being described as a sleeve that the 125mm twin wall sits inside it? Or is it actually an insulated twin wall flue in itself?

 

[ProDave]

I have looked but I can't find it listed where I bought mine from.  It is just a fireproof insulated sleeve that goes around the twin wall.

 

In practice, the outside surface of our twin wall is barely warm to the touch and would not threaten even a piece of paper from igniting, but that might be very different with the pipe encased in insulation.  Whatever you do, don't do it without the approval of your installer.

[Oz07]

1 hour ago, ProDave said:

When I did mine, I used an insulated sleeve, supplied by the flue supplier for the purpose.  It was 50mm thick and obviously fireproof and thus everything else gets the 50mm from combustibles it needs.

 

How did you maintain the airtightness with that arrangement? Did you get something like @JohnMo said?

[jimseng]

Quote

In practice, the outside surface of our twin wall is barely warm to the touch and would not threaten even a piece of paper from igniting.

Indeed, but it's the regs I have to follow!

[dpmiller]

We used Shiedel's Ignis Protect to deal with heat protection and airtightness