Twin wall flue shielding

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Andy72
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Twin wall flue shielding

Post by Andy72 »

Hi, I am putting twin wall flue pipe through joists at first floor level. The regs say 80 mm between the outer skin and combustible materials. My joists are at 400mm centres which gives me a net 340 between joists. The flue I am installing is 180 mm internal, 230 mm external leaving only 120 mm ie 60 mm between the outer skin and combustibles. Is it permissible to install a heatproof shield on non combustible material to face the joists either side and by doing so reduce the distance required from the pipe to the joists? Or do I have to reposition sections of the joists?
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Polarengineer
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Re: Twin wall flue shielding

Post by Polarengineer »

When the rules cannot be met (if you happen to know them) one should refer to the intention of the rules and one's common sense. In your case, my solution would be to prevent the joists becoming heated from any radiation from the already insulated pipe. So belt and braces, I would line the joist with plasterboard for a short section and then glue a ceramic tile to it, no potential heat transfer will ever reach the joist. I would sleep well with this fix.
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Re: Twin wall flue shielding

Post by RobertArthur »

A well-respected company here in France is Poujoulat. Their website shows this summary, see the safey distances of 10 cm in their picture: "cheminées double paroi non isolés".

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Re: Twin wall flue shielding

Post by Andy72 »

RobertArthur wrote:
Tue Sep 15, 2020 11:14 am
A well-respected company here in France is Poujoulat. Their website shows this summary, see the safey distances of 10 cm in their picture: "cheminées double paroi non isolés".
Thanks Robert. I had read their guide but it doesn't mention shielding combustibles with a non combustible material as an alternative to removing the combustible material. That is the answer I'm seeking but cannot find.
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Re: Twin wall flue shielding

Post by RobertArthur »

Andy72, not having access to the full text of these DTU 24.1 regs, only this type of introductions, I don't know what fixes are mentioned in these regs. Polarengineer already came with a possible solution, I was thinking of a " heatsink" analogy (poweramplifiers). A third piece of single flue (20 cm) in between, fixed at three points. Thermal reflection and chimney effect. A workaround, probably not mentioned in the regs.

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Re: Twin wall flue shielding

Post by Le Démerdeur »

Placoflamme.

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Re: Twin wall flue shielding

Post by Annabelle's Papa »

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Re: Twin wall flue shielding

Post by Andy72 »

Time is at a premium. In needed to get the flue fitted and so I decided to cut through the joist and put in a splint to reinforce the cut and meet the distancing requirements that way. Thanks to all those who replied.
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Re: Twin wall flue shielding

Post by Polarengineer »

Well done. Job done, move on.
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