flue liners

[bracken]

ayup all,

just a quickie do I need to put in a flue liner for a wood burner if my chimney is sound?

I have been told I do not have to.....slightly worried if I dont buildings control will get upset!! on the other hand it will save me nearly £1000

Please advise anyone

Regards B

 

[chuckey]

How sound is your chimney? Unless it has been rendered with some special substance the lining will decay with the acids produced when burning wood or coal. my 200 year old cottage never had a lined flue, so now the bedroom has been decorated for the first time in 47 years, the tars in the wall its self are leaching out and appearing as a stain on my nice white paint. Also if the house is more then about 50 years old there is a good chance that there will be cracks in the flue and walls so you may find more smoke about then you expected. So the choice is up to you.
If you are a DIY person, then I would think that £1000 for a flue liner/terminal can easily be beaten. I did my own, hardest bit was having to go up and down the ladders about 6 times.
Frank

 

[bracken]

Thanks for getting back to me,

I thought this may be the case yes I will line the chimney my cottage is over 200 years old and I fear the chimney will be tired....

Thanks B
North Yorkshire

 

[Penners]

There have been several threads on this subject over the past few weeks.

The important thing is that your flue liner should retain the heat in the flue gases until they get to the top. If they cool on the way up, you'll get condensation of acidic combustion products within the liner, which can corrode it surprisingly quickly.

If you are installing an insulated liner, this will help to avoid this problem, but ideally it's best to add extra insulation around the liner, too. This can be in the form of a specially designed jacket, or - if your chimney isn't too massive - by installing a register plate above the fireplace and filling the entire void between the liner and the walls of the chimney with vermiculite.

What you should absolutely not do is install a single-wall flexible liner without any insulation. It'll last a very short time before crumbling due to corrosion.

 

[Flyfisher]

Just to add to the confusion, I was out today visiting stove shops and talking about liners. One shop told me they no longer insulate chimneys or liners; just use the double-skin liners with no insulation, apparently. They reckon it's better for the liners (they don't overheat and burn out). I had specifically asked about this because the chimney I'm currently working on is so big that filling with vermiculite doesn't seem practical so I was going to use the 'jacket' approach. Now I'm just thoroughly confused - so I thought I might as well share it!

While on the subject of liners, am I the only one to have noticed the very wide range of prices? I've seen between about £20 and £58 per metre for 7-inch double-skin, 316/316 stainless steel liners. Presumably 316 s/s is a specification in itself so the only other variable I can think of is the thickness of each lining, but this doesn't seem to be widely stated.

Any suggestions about how to choose between such a wide range of prices - just pick a price in the middle? Or any specific recommendations?

 

[chuckey]

My flue liner is 316/329 stainless steel, the 329 being paperthin, so I guess its a very expensive corrosive proof liner - contains 29% chrome!!(?)
Frank

 

[Flyfisher]

I've only seen 316 or 904 stainless options for chimney liners - as 316/316, 904/316 or 904/904.

Is the 329 s/s used for special applications or does it come with a longer guarantee (I'm assuming it's more resistant to corrosion, but that's a guess).

 

[chuckey]

Can't find 904 in my machinery's handbook (American), however on :- http://www.rolexforums.com/showthread.php?t=52891 , people claim it is 26% chrome. So better then 316 same as 329?, perhaps a "Euro" number.
Frank

 

[Moneypit]

316 has 16-18% Cr, 904 has 19-23%. Don't be misled into thinking that a 3xx steel has xx% Cr. The important difference for 904 is that it has 23-28% nickel compared to 316 at 10-14% (which is why it is much more expensive). The high amount of nickel and 1-2% copper is what gives 904 much greater corrosion resistance, especially to pitting corrosion in sulphuric acid environments.

Oddly, it is not recommended for use above 400 deg C whereas 316 is good for over 800 deg C. Given that our Clearview stove casing reaches over 350 C it's hard to believe that the gases going up the flue aren't a fair bit hotter.

Both 316 and 904 are austenitic stainless steel whereas 329 is a ferritic/austenitic (so called duplex stainless grade). 329 has a Cr content of 23-28% but only up to 5% Ni. Duplex stainless steels have greater corrosion resistance than austenitic such as 316, but probably not that different to the preferred 904.

A basic rule would probably be the more it costs, the better it is.

 

[Schoolmarm]

Just to upset us all even more, the old house book I am reading at the moment says liners only last 10 to 15 years then need replacing.

How on earth are people going to replace them that frequently, it always seems like a huge job.


I may have done something really stupid with our fireplace.

 

[Penners]

I may have done something really stupid with our fireplace.

What? I can't believe any more so than the rest of us.

 

[Flyfisher]

I've also read that 904 grade s/s is recommended if you're burning smokeless fuels whereas 316 grade is OK for everything else. So 904 grade might well be more resistant to corrosion but it may be over-specified for most installations.

The 10-15 years replacement cycle is a bit worrying - it could easily add £100 per year to the running costs. But what's the alternative once the liner is full of holes?

 

[Schoolmarm]

I may have done something really stupid with our fireplace.

What? I can't believe any more so than the rest of us.

We built the register plate into the fireplace using the slab of concrete that was previously in the old reconstituted stone fireplace.
This means that there is now no way to access above it and do any replacing of liners. It is sort of coursed in, but hidden, above lintel height.

We then left all the old clay liner in place, (because we couldn't get it out), poked the fire flue up inside the clay as far as possible and sealed with a pyramid of bricks and lime mortar.

THEN................carried on building the fireplace up to ceiling. I will now need a jcb to drive through it to replace any part.

I hasten to add, by "we" I mean we allowed a man to do this. And I insisted he did all that overkill because I was concerned that it needed sealing properly.

I think this means that even if we wriggle the flue pipe down and out, we still can't put a proper liner in as the width of the bottom part is narrower than it should be.
I bet this is as clear as mud. :roll:

 

[yamin]

Don't know if this helps or hinders and CERTAINLY no expert or knowledgeable opinion. However, for what its worth, we had our log burner in one room with chimney in good repair but no liner. This summer we moved the log burner to another room and had it refitted with the double skinned flue thingy everyone talking about here.

When log burner in open chimney with no liner it was an absolute PIG to light and put out minimal heat. Now in another room with twin skinned flue, it lights like a dream and throws out so much heat you have to back off.

Not sure of the mechanics/physics etc of that - someone here can tell you, but from a purely lighting and getting the benefit from point of view, I'd always go for a twin skinned flue (ours uses the void of a chimney)

Yamin

 

[Penners]

We then left all the old clay liner in place, (because we couldn't get it out), poked the fire flue up inside the clay as far as possible

I'm not sure about the advisability of allowing a woodburner to vent up a clay liner. Maybe this would be OK (anyone know?). So if/when the day comes that your steel(?) flue deteriorates, perhaps you won't need to replace it - just rely on the clay liner.

But if you do have to do major surgery, my advice would be that, whatever happens, you should ensure that you drive the JCB yourself. It's fun!

 

[shelli]

Stoves online say this about their flexible flue liner - whaddaya think? - looks fairly flimsy on the pic

http://www.stovesonline.co.uk/wood_burning_stoves/Flexible-Flue-Liners.html

Oh and question - what about Rockwool sleeves -anyone got any experience, good or bad?

 

[Penners]

Well, they say that they'll guarantee it for ten years, which I reckon is quite surprising for a single-skin flexible liner. I wonder whether the guarantee is wrapped up in various conditions and disclaimers about the method of installation, etc.

As for Rockwool sleeves, as has been mentioned on the forum many times, if you can keep your liner well insulated you've got a much better chance of minimising the corrosive tars that can shorten its life.

 

[shelli]

So Penners

What I was hoping to do was sort out 2 flues with flexi liner and rockwool sleeves for the price of doing one flue with rigid double walled pieces (at £125.00 per metre :shock: ) But I am cycnical and therefore dubious about anything that seems cheap intitally.

If there are no preconditions and tricky installation smallprint it would seem to me that 10 year guarantee might be as good as we are going to get. - As much as I'd rather not be the cautionary tale I might just get on with it and let you all know

When you have thrown as much hard earned caash at a house as we have whats another grand on the cosmic scale of things :shock: - cant believe I have become so blase about money

Shelli X

 

[Flyfisher]

Shelli, it sounds like we're having the same dilemma. Last week I had settled for a double-skin flexible liner (316/316) with a rockwall insulation sleeve. Then I was told by a stove shop that insulation is no longer recommended or necessary. Actually, I quite like the idea of a bit of heat getting into the chimney structure.

I've not yet investigated the 10 year guarantee smallprint but if it doesn't mention insulation as a requirement then I presume it must be OK without. I guess that the tar/acids condensation issue will be very variable depending on how the stove is used. I've read that wood burns most efficiently at high temperatures so it's actually better to have a 'quick blast' than a 'long simmer'. I imagine this sort of use would also minimise tar/acid condensation regardless of liner insulation.

I've been quoted £58 per metre for 10m of 7-inch double-skin flexible liner, which seems a bit on the high side judging by online prices. 6-inch was £46/m.

I really need to make a decision this weekend and am beginning to think I'm over-analysing the whole thing.

 

[shelli]

Graham

You have obviously spent several long hours on research too!! Maybe you can tell me....What is difference, if any, between flexi double-skinned flue liners and rigid double walled ones - apart from flexibility of course - and seemingly the price - is there a diference in sturdiness?

and if not really then who does double skinned flexi liners - any good links?
thanks

Shelli (thread hijacker)