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Wood-burning stove experts, please?

John A.

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After 4 trouble-free wood burning years we have now had a year which has changed all that. 

After the stove was installed (it's a Supra Alsace) in 2003 we thought it was our best ever

investment - it heated the whole house, it was effortless to light, lasted all night with the damper

pushed right in, it would burst into life in the morning half an hour after pulling out the damper

- in a word, a dream!

However, our troubles started in February this year, when we started waking up in the mornings with

muzzy heads and an unpleasant odour in the air. Turned out to be 'les emanations' from a hole in the

back of the black enamelled pipe going from the stove top up to the register plate (plaster actually).

The pipe slopes backwards slightly because the flange in the top of the stove is slightly forward

of the chimney cavity above, so resin had been running down the seam at the back of the pipe and

finally eaten its way through the pipe.

We then had the black pipe changed for a stainless steel one. All was ok - for 3 nights. On the fourth

night we woke at 2 am with a smell of resin throughout the house. I lifted the top from the stove and

there was black resin flowing out of the join between the stove flange (male) and the pipe (female).

The next day I took the insides out of the stove, cleaned everything thoroughly, swept the chimney

with my neighbour's brushes, carefully put mastic over and into the joins between the pipe and the

stove's flange - inside and out, and put all back together and started up the fire. I also put new

seals around the door window.

Great, all ok .... for the next two nights. Then, 2 am on the third night the familiar resin smell.

Lifted the top of the stove again - there was the old black magic running out of the joint again!

In great depression we left the house - couldn't stay in it with that smell - and came back to England

to take stock. What on earth do we do? Our wood has always come from the same source - our neighbour,

who we get on well with, who leaves his wood for 2 or 3 years at least in piles under black plastic

sheets in the fields before using it or passing it on.

Speaking with 'experts' in the pub back here we are now wondering if our downfall might have been our

normal practice of putting a large log onto the damped-down stove before we go to bed at night - to

keep it going all night. We are told that you should always put a new log onto a lively fire and let

it flame for 20 minutes before closing it down for the night. Also, maybe we should be splitting the


Does anyone have any suggestions, or similar stories? Does anyone know where I can get a log-splitting

machine for 50 cm logs near Poitiers? - I don't relish the physical prospect of big logs and axes at my

time of life.

We really wood be grateful for any suggestions for sorting out our dilemma!

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I've used logburners for thirty years,  now I have three, and and my comments are:

Fit a correctly oriented stainless flue all the way from the stove to the exterior, with flue and chimney protected from rainfall. The flue, which warms quicker than a brick or stone chimney because its surroundings insulate it, creats less condensation and any that is created stays in the flue and returns to the fire.

Wood smoke (and far worse-coal smoke) leaves deposits in the chimney and then condensation on the cold surfaces during slow burning carries these and fresher deposits down the chimney. Generally burn the stove at a higher heat and ensure that the fuel is dry when it is put on the fire - store it indoors and then near the stove for a few days before use. That way the deposits in the flue become cinders, if you have a clear window type stove it is unlikely that the door draught will permit it to burn slowly enough to stay in overnight or create condensation in the sts flue

Do not burn pine or excessively resinous woods. Sweep the flue twice each winter after a hot burn.

It is important to choose the correct stove size for the heat requirement so that it can be burnt at its designed operating temperature without the room becoming too hot.

Hope this helps.





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If it was installed in 2003 it will

still by under guarantee so I would get the installer back in to sort

out the problems.

As an aside, they guy who swept my

chimney last week was saying that as last winter was warm, chimneys

were generally worse now because when the weather is warm the air

does not rise up the chimney so fast and thus more crud

settles/condenses/sticks to the pipe. No idea if this is true but he

was a professional guy.


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It's not clear from your description of the installation but you need a liner to the top of the chimney - this will solve most condensation problems. Getting the flue pipe vertical will also help. What type of wood are you burning? Any wood is acceptable except pine. Walnut and very dense types tend to give out very little heat, the best is oak or chesnut.
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Thank you all for the advice. Some comments .....

We have a flexible flue liner joined on to the top of the initial (inflexible) 4 foot stainless steel pipe. The flexible liner goes to the top of the chimney, where it has a clip holding it in place. About 5 inches above the top of the pipe, which just pokes out of the top of the chimney, is a paving slab sitting on 4 pairs of bricks at the corners of the chimney walls - so it is difficult for rain to get in. We don't have any insulation in the surrounding gap in the chimney.

Steve's reply confirms my suspicion that we are using the stove at too low an operating temperature. When winter is at its coldest the stove is just about the right size for the house - we keep it on high heat all the time. But what do you do when the weather is not so cold but you still need some heat in the house? In this situation we have been running on low heat. Maybe we should have been turning it up and opening some windows to get rid of unwanted heat.  The stove has a glass window, and for the first three years it regularly kept going perfectly well overnight - at low heat - and we were able to revitalise it in the morning by pulling the damper out.

I think the wood we are using is mainly hornbeam, some hazel and some oak.

I thought my guarantee was just a couple of years, but I'll check. Presumably the installer would say that the fact that the system was working perfectly for 3 years means the installation was ok. I don't think my command of the French language would get me a lot further than that.

To get the rigid pipe completely vertical would require either chiselling away 3 or 4 inches from the wall at the back of the fireplace or buying a different design of stove. It may yet come to one of those options.

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Three suggestions.

First; perhaps the core problem is that with no back-filling insulation in the chimney void, the higher parts of the liner are losing too much heat.

In this case the draught will be reduced, making the fire combust less completely, leading to condensates as partially combusted fuel means burnable hydro-carbon is escaping into the chimeny. The colder the upper parts of the chimney, of course, this will cool the condensates, rapidly and lead to them condensing out.

Solution: A rockwool insulating jacket. Downside is that the liner needs extracting in order to fit the jacket; and after four years in position, it's probably heat-tempered and may well break.

Secondly, try using a chemical "Sweep" product; many are bad for Inox, but there are products around for woodburners which are perfectly safe to use on Inox liners.

This should burn off any condensate deposits by chemical action.

Modern woodburners have a thermostat which closes the air flap if the temp becomes too high. The stat is a simple mechanical device, normally, with a capillary tube. It might have "died" and as soon as it heats up, it closes the flap permanently, thus restricting air and ensuring imperfect combustion.

Just a thought.


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I have a list at home giving the woods that produce the best heat/burn rate. Oak is second best, Hornbeam is THE wood for slow burn and maximum heat.

When I installed a pellet version of these in the UK, we put vermiculite (undoubtably spelt wrong!!) which made a hell of a difference, could this be put behind a wood burn insert??

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Hi, double layered flexible metal flue liners are reputed to last between 5 and 10 yrs, except where a lot of corrosive condensates are produced. Having already had a problem with what sounds to like an enamelled stainless steel pipe (1mm thick wall) fitted directly above the stove,  I would suggest you also have a problem with the flue liner. The flue liner is made from thinner material, so  if the solid wall pipe has corroded, you can bet your bottom dollar that the flexible liner has too. Condensates cause most problems when the heat in the flue liner does not remain at a sufficiently high temperature to evacuate the fumes, and it sounds that by constant use of the damper you have achieved this scenario.

This is what HETAS has to say on the subject:

These liners are for relining an existing brick chimney and are not to be used as a liner for new masonry

chimneys. Liners for new build are referenced in section D. These liners should give a normal life of 10 years

or more when correctly installed, used and maintained. However, these flexible liners whilst being easier to

install and replace are not permanent and prolonged periods of slow burning particularly using solid fuels,

combined with inadequate cleaning of the flueways can cause corrosion damage which reduces the expected

life of the liner to less than 5 years. If there is a risk that these conditions can occur the non-metallic liner

systems are recommended and under normal use should give a life equal to that of the dwelling.

Hope this helps or at least clarifies.

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Oh dear! I thought one thing that was ok was the liner. No sign of tar

running down the outside of it , no  smoke in the space between the

liner and chimney, no problem with the fire drawing .. but I'll add it

to my list of potential woes - sounds like it could be near the end of

its life so may was well replace that as well. Heigh ho.

Many thanks for the information.

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I think your problem could be one of two things.

1. Condensation building up because of the type of wood you are using, or condensation in the chimney flu.  You could, re-chimney flu , install a full length of pipe from the top of the woodburner to near chimney outlet on the top of your house.

2. This could be a tar build-up caused by years of wood not being hot enough in the woodburner, which in turn leaves the sticky deposit on the chimney flu itself, this gives a sort of runny substance between tar & creosote you are talking about. 

Stovax make a product which you put on the woodburner whilst it is hot which helps to overcome this problem.

Hope this advice helps!  Godd luck


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John A said "there was black resin flowing out of the join between the stove flange (male) and the pipe (female)"

When I installed our rigid stainless steel chimney liner 6 years ago I was told to put the female ends upwards to avoid condensate running down the outside.

I did so. It doesn't.

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The flue of our woodburner was installed the wrong way round (with the female ends looking downwards). Lots of tar was running down on the outside. We called our installer back and he turned it round and we have no problem now. Our next door farmer told us that Elm is the wood which you can burn after 18 month as it has no Creasote (how do you spell that?) in it.

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Thanks for all the advice. From what people say it looks like we have male-female problems with our pipe joint, probably a worn-out liner and an unpleasant legacy from 3 years of bad wood-burning habits. I have constructed a letter to the installer to get his opinion and will keep the Forum posted as we progress.

Thanks again.

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