Single Wall vs Twin Wall flue for section inside house? Pros and Cons...

[carbs for arbs]

Hi 

 

Back again with a second wood stove query, if anyone would be kind enough to share their thoughts please...

 

We're planning to have a stove fitted into a single storey room.  The stove has a 5" flue.  The installers who have quoted said they think the flue will need to be a total height of 4.5m.  It will be a straight run, no bends.  If there were to be a single wall flue in the room up until where it has to change to twin to pass through the ceiling, the single wall section would be around 1.6 to 1.7m.  The rest would be twin wall, although most of it would be outdoors.  

 

We only burn well seasoned hardwoods.  

 

From what I've learnt, the advantage of single wall would be more heat to the room.  One installer said he thinks for each 1m of single wall flue you get 1kW of heat, which would be a great bonus.  I'll also admit a bias - I think the stove looks so much nicer with the single wall 5" flue.  I've only found a couple of photos online where the same stove has been installed with twin wall and to be honest I think it looks f-ugly.  Also, more space on the stove top for a kettle etc would be an extra bonus.  

 

However, I've also learnt that the advantage of twin wall is the flue maintains a higher internal heat, creating a better draw, which results in a stove that is easier to start, runs better, and a flue that doesn't block with creosote so much.  (Although I should add that some say they have none of these problems with single wall).  

 

It seems to be a very divided topic, with strong opinions on both sides.  While I want the aesthetics and extra heat to sway me to single wall, I also don't want a stove that is tough to light and doesn't run well.

 

So over to you guys for some thoughts and insights...

 

Many thanks

[monkeybusiness]

Will it not look odd where it changes from single to twin wall? 

[carbs for arbs]

You're right, it will, and it's something I'm not overly pleased about.  However, I'd be much happier with the change from single to twin than I would twin all the way.  Lesser of two evils I guess; although "evil" might be over-egging it a bit!  

 

Thanks for your reply

[monkeybusiness]

5 minutes ago, carbs for arbs said:

You're right, it will, and it's something I'm not overly pleased about.  However, I'd be much happier with the change from single to twin than I would twin all the way.  Lesser of two evils I guess; although "evil" might be over-egging it a bit!  

 

Thanks for your reply

I’m at a similar decision-making junction myself at present!

If you find a good (ie cheap!) twinwall supplier please let me know….

[openspaceman]

You need to check part J of the building regs, I thought you were only allowed 400mm of single wall above a stove.

[Muddy42]

Can you just clarify that you are not just lining an existing chimney, but putting in a totally new run in what is presumably a modern house?

 

Assuming its the later, I agree with you that visible twin wall flues look horrible.  Personally I would go with single wall in the house and twin in the roof.

 

BUT you need an installer that you can trust, that should be able to advise you.  This also should make it compliant with the various regs and you have more justification to go back to them should something go wrong.

 

Unfortunately (and I've posted about this ad nauseam) modern stoves have very precise tolerances for draft, flue height, flue insulation etc. Get it slightly wrong and the stove will smoke into the room.  The stoves operating manual will advise you.  Plus because modern houses are airtight, stoves sometimes need a dedicated piped air supply from the outside.

 

I spoke to these guys before buying and they were really helpful.

Search results for: 'liner'

WWW.STOVESPARESLTD.CO.UK

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UK premier supplier of woodburning & multi fuel stove spares & parts at LOW prices with fast delivery.

 

[dan blocker]

You can go in single wall up to 400mm from ceiling. It must be twin wall from 400mm below ceiling and through the ceiling and roof structure to the termination of chimney. 

[openspaceman]

1 hour ago, dan blocker said:

You can go in single wall up to 400mm from ceiling. It must be twin wall from 400mm below ceiling and through the ceiling and roof structure to the termination of chimney. 

Thanks for that, I misremembered  but knew 400mm came in to it

[carbs for arbs]

Many thanks for the replies.  

 

On 05/02/2025 at 11:39, monkeybusiness said:

If you find a good (ie cheap!) twinwall supplier please let me know….

 

Sorry but we'll be leaving buying the flue etc to the installer so I can't help you there I'm afraid.   

 

 

On 05/02/2025 at 15:29, Muddy42 said:

Can you just clarify that you are not just lining an existing chimney, but putting in a totally new run in what is presumably a modern house?

 

 

Apologies, I should have made it clearer.  Yes, there's no chimney or fireplace recess.  It will be freestanding in a corner, with rigid flue all the way.  It's a 25 year old extension on a much older house.  

 

 

On 05/02/2025 at 15:29, Muddy42 said:

Assuming its the later, I agree with you that visible twin wall flues look horrible.  Personally I would go with single wall in the house and twin in the roof.

 

I'm glad I'm not alone on thinking it looks awful!  But the whole "function over form" question is sometimes a difficult one to resolve...

 

Yes, we'll make sure we used a reputable and trustworthy HETAS registered installer.  We've had a few quotes and even amongst installers the single vs twin wall opinion varies, usually with a strong opinion on one side or t'other.  Same story on old forum threads, and internet articles.  Seems a really divided topic, so any further thoughts and opinions much appreciated before I bite the bullet.  

 

Cheers