Extending my Flue

26 Aug 2014
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United Kingdom
I am currently undergoing a extension on my house and I need to extend my Worcester Bosch Greenstar 30i boiler flue. At the minute the boiler flue has a simple horizontal extension kit on but I need to extend the flue up vertically into the floor space the approx 1900mm underfloor and out of the new external wall.

My questions are can i do this myself safely and legally and in terms of the vertical adapter and extension pieces would it be ok to buy these off the likes of EBay etc..
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In a word NO. What your proposing isn't allowed anyway. Plus have you got the knowledge/equipment to test the flue integrity once done ? Do yourself (and your family/neighbours) a favour and get professional advice.
Thanks can you elaborate on why it is not allowed and what is not allowed about it as this could be a major problem as I do not want to move my boiler to a external wall?

I understand why a professional should do it and point taken.
Read TB008 from the Gas Safe Website.

Not sure what your flue length restriction is but I seem to remember the Wooshitter Botch is pretty restricted.

Anything to do with flues and boiler relocation needs a Gas Safe engineer who knows his way round an FGA.
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I have read the instalation manual with my boiler and the length I can extend is 4m in 100mm and 13 in 12 mm so I am pretty sure I can extend it the 2m I have to.

Again thanks your reply is much appreciated.
Equivalent length?

I see your paltry 13 metres and raise you 64 - which i think my boiler's limit is.

But i have a low opinion on Wooshitter's current crop.
What do you mean equivalent length?

You can keep you 64 I only need 2 Lol☺
Ok err thanks but can you please explain what is not allowed? I understand I am not allowed to do it and I now won't be doing it.

Is there any chance I can get a straight answer please I really don't meam that in a rude way but I only want a straight answer in layman's terms.
You won't meet the regs regards TB008, you probably won't get the required fall.

You might be too close to combustible surfaces.

I haven;'t the inclination to read your boiler manual, but the equivalent length of the bends have to be added to linear length of flue which also needs adequate support.

There are probably a few others that are lurking somewhere in the region of my brain that is designated "easy when you know, too long winded to explain".

In short - you will never meet all the requirements, and if you can't meet ALL of them then it can't be done.
Thank you for your time in explaining that, even with equivalent bends it would be well under the 4m as it is only going up approx 200 - 300 mm then a 90 degree bend then 1.9 of straight flue so I am pretty sure I have enough.

All of that doesn't seem to be the problem as that seems to be the fact it is in the floor space if I am reading your reply correct.

I really do not want to move my boiler any suggestions. (I know you have seen the job but any suggestions will help)
Basically you can't build your flue into the ceiling it needs to accessible for inspection etc

Google TB008 as suggested
I was just reading TB008 can i not just make that part of my ceiling accessable with hatches etc
At 1.9 m in the floor void even with hatches and clips etc the fall would be to great for the space ( including the non combustion regs etc) your best bet would be to get a Worcester approved gas engineer who deals wit these everyday and they could tell you the best options for your boiler

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