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Wood burning stove flu full of ash & goo!


mmaddock
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Just been investigating why our wood burning stove doesn't seem to be operating as it was, minus 6C outside is taking its toll and we need the stove back to roasting hot again!

I bought an extension to the flu to extend it further up the chimney because I thought maybe it wasn't drawing properly, but on removing the 90deg bend in the flu before it goes up the chimney, the problem becomes immediately obvious - it was almost entirely blocked with ash and a horrid gooey tar.

I've cleaned it out as best as possible, and it is working again - but obviously it is going to re-occur.  Does anyone know if there is any sort of product that I can use on the flu - maybe some sort of internal coating that would stop this stuff sticking to the flu?  Or is there something you can burn in the stove to clean the flu out now and again?

Cheers,

Matt

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Could possibly be the result of burning unseasoned wood, I'm told that 2 year old Oak is best but it's not going to be the the cheapest of course.

Also Sounds like it hasn't been cleaned regularly either and with a 90deg bend in it I can imagine it's probably quite difficult to do so.

I don't know about any sort of inhibitor to prevent buildup I'm afraid but I think if you stick to seasoned wood and regular sweeping you shouldn't have a problem. Might be an idea to reduce that bend though if at all possible.

Note: I understand that some insurance companies expect you to have your chimney swept annually and could conceivably refuse a claim if it hasn't. Would be a good idea to check your policy.

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The wood is very well seasoned - in fact almost too much so - it burns like mad on full blast (when the stove is working well).  I was told it had been sat for around 10 years, which I'm sure isn't ideal - but I was desperate, and it was very cheap from a friend of an aunt of a friends mother - or something like that - you know, the typical French thing!  The stuff I bought for last winter from the local supplier (at some stupid price of 54€/s) hadn't been seasoned, so it is waiting until next year.

This particular stove / flu has only been in for a few months, so the crud has built up in a matter of months - I wouldn't have thought I should need to clean it that often, especially as it has only been running on a daily basis for the past month or so.

I don't think the 'corrugated' bend helps much as it gives lots of sticking points on which bits can stick.  What I may do is try and get an adapter to enlarge the diameter of the flu to allow better flow - it is one of the smallest ones at 97mm.

Matt

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OK so the wood is seasoned - you don't say if it is hard or soft wood, but the description of how it burns suggests soft wood - not ideal and it will give you lots more tar than hard woods do.  But if that's what you have got, that is what you have got and you can burn it (gives around 75% heat output of seasoned oak plus the tars)

 

Possible aid:

Buy a buche de ramonage (sp) from your local brico house or even Gamm Vert.

Instructions are on the pack, but basically burn it on its own in the fire - takes about 1 hour.  This will convert the tars to a cindery mass which will fall off the walls of the chimney.  Like you, we have a right angle bend and the likely consequence is that the falling debris will block the bend - if it is anything like ours.  It is however very easy to dig out with a garden trowel, and we then have 6 months problem free drawing on the fire.

 

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I'm really glad you have found the ash and goo in the flue before you set fire to the house as I almost did! [:'(] I'm sure there'll be an avalanche of advice about getting the chimney cleaned once a year - I learned the hard way! I did know you should, but I kept thinking as it was a second home and it hadn't been used that much, it wouldn't need it yet. Wrong! I hope others will take this as cautionary tale! [:'(][:(]

It's amazing how time flies when you're having fun, but we really hadn't realized it was actually about 6 yrs ago that we put the stove / flue in new!

I was on my own in France at the time - actually this October - I was on the phone to hubby in the uk one evening, when suddenly I began to hear the sound of something falling down the flue pipe on the poelle in the kitchen, then I noticed that the pipe had begun to glow red!! I stupidly said "it shouldn't be red, should it?" within a minute the red glow had crept further and further up until it had almost reached the wooden boarding in the chimney! "I've got to go!" I shouted, and flew out of the house to get my ever obliging french neighbour who came running in. He put on the fireproof gants and got his wife to get a huge tin bucket. He pulled the poele forward a bit and pulled the pipe away from the back and it fell into the bucket, red hot ash and all!! He was excellent and I know without him there would have been a disaster. I was so grateful and scared.

I got a well deserved ticking off for not cleaning the flues and was told to get two buches rammonage the next day (we have a stove in the lounge as well) I did and used them both, although the kitchen one had been emptied! He said to send off the certificates that came with them for the insurance, but I'm not sure they will accept them as proof I have have the chimneys cleaned, will they? I was going to go into the office on our next trip and ask them.

This was a lesson very well learned! [:$]

Carole

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[quote user="mmaddock"]
I bought an extension to the flu to extend it further up the chimney [/quote]

Your flu liner must extend all the way to the top of your chimney anything less is dangerous- how high is your chimney and how high is the flu up inside it??

 

 

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Looks like your problem is the simple 90deg bend, This is only suitable for ventilation. I notice that my french supplier does not stock such an item only a double 45 deg which gives the bend you need but also allows ash and tar to disperse try  www.poujoulat.fr and look under 'tubaginox rigide', me granny used to have cast iron bends with an access hatch built in but I'm not aware of any suppliers today. 
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mmaddock, thank goodness you found a serious problem before it became a disaster. The European regs state that you must not use 90' bends in a flue anywhere except immediately behind a burner (if it is rear vented). I think you have inadvertantly discovered why. It is permissable to use upto 2 off 45' bends, but the advice is still to have none if at all possible.

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[quote user="clarksinfrance"]One other quick bit of info, it is required (by law) to have a chimney (also read flue) swept twice a year, once during the burning season; and once during the warm season.
[/quote]

Do you mean that (some) insurance companies require that you have your chimney swept once a year and obtain a "certificat de ramonage" in order to validate you insurance?

 

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[quote user="clarksinfrance"]One other quick bit of info, it is required (by law) to have a chimney (also read flue) swept twice a year, once during the burning season; and once during the warm season.
[/quote]Twice a year, is it really law ?

If so a big surprise to many I suspect.

Got a link to a page perhaps, one specific to French regulations not European ?

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I have asked our insurance if they require a yearly certificate and they said "non"! However it is a good idea to clean your chimney at least once a year, especially if it is your main residence, but I can't quite see the urgency for a "maison secondaire  (or perhaps use the special "briquette" which I have even seen in Super U, there is a form inside to complete)
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CLEANING THE CHIMNEY

The chimney cleaning (mechanical) must be done twice each year, once being during the season of use. It must be done

by a qualified company which will issue, after the work, a certificate of cleaning.

Taken from

INSTRUCTIONS FOR

INSTALLATION AND USE OF

STOVES AND INSERTS

CONFORMING TO THE EUROPEAN STANDARD EN 13229

sorry I can't provide a link to the live document, as they have to be purchased, and they are about €85

Just in case anyone is in any doubt, the EN 13229 document has been subsumed into the NF and has the same identifier:

NF EN 13229

Juin 2002

Foyers ouverts et inserts à combustibles solides - Exigences et méthodes d'essai

Indice de classement : D32-308

Statut : Norme homologuée

Document modifié par les amendements : NF EN 13229/A1:Octobre 2003 (D32-308/A1) , NF EN 13229/A2:Juin 2005 (D32-308/A2)

Norme élaborée sous mandat donné au CEN par la commission dans le cadre d'une directive Européenne :

DI 89/106 01/12/1988 Directive relative au rapprochement des

dispositions législatives, réglementaires et administratives des états

membres concernant les produits de construction.

Support d'une marque :

NF 009 Appareils ménagers utilisant les combustibles liquides ou solides

Hope it helps (sorry for the underline here, it has held on to the formating from above)

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If this is the law then I am  guilty of criminal negligence and thousands of other homeowners and everybody who uses the "cleaning logs"and the stores who sell them. My insurance provider (AXA) does not require a yearly certificate (I kept the e-mail just in case!) This really needs further investigation.
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[quote user="Monika"]This really needs further investigation.[/quote]I agree. It's stretching the bounds of credibility that if this is law then nobody has brought it up before, it's a pretty vital point I would say.

I have cribbed the following from another THREAD - with thanks to Clair

[quote user="Clair"]I am covered by the MAAF. Under 'Fire and similar events', they say:
[quote]our advice:
think about having your chimneys and boiler cleaned and serviced before the winter
have you gas appliances checked
have your insert fitted and checked regularly by a professional
...and other advice...
exclusions:
any burns caused by smokers
damages caused by use of dynamite or other explosives (except fireworks)[/quote]
Note: not recommendation, not requirement, but advice

Even if they did require us to produce a certificate to prove an annual sweep, we would still do it ourselves as well, several times a year.

EDIT after re-reading the question: the MAAF have told me that as long as the chimney is swept clean, they have no problem with who does it and do not require a certificate.
[/quote]

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Regardless of the on-going debate, many thanks to those who replied with help.

The 90deg bend is right behind the stove because it exits to the rear, so there is no choice.  At the moment it is running with a short extension from the stove (about 30cm) and then the 90deg bend - there is more than enough draw to pull the smoke up after that (it almost pulls it up straight out of the back of the stove, but I have it pushed out into the room a bit so less of the heat goes up the chimney!) I'm not sure about the usefulness of adding more pieces to the flu, because adding more flu only allows the junk to build up in it and then fall back into the 90deg bend, whereas this way it disperses into the chimney just like it would with an open fire.

There is a futher complication in that I checked out the stove and the flu doesn't actually go straight out the back, internally the flu vent exits in a different place to where it comes out at the back (hard to explain), but that hasn't helped because it has obviously blocked up internally within the stove - which explains why I couldn't get it going properly even with the flu off.

Anyway, I have today burnt one of those Buche Ramonage in it, and now it is going like it always did - so many thanks to those who suggested that.  I'll stick one of those on a month during burning season and hope it keeps it clear.

On the subject of chimneys, I do recall our fair share of chimney fires from when I was young - what fun to see flames coming out of the top of the chimney pot! (well, it is as a kid!)  Never ever did any harm to the house.  I believe the only time you have a real danger of your house burning dow is when someone put the beams into the chimney brest.

Matt

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[quote user="mmaddock"]Regardless of the on-going debate, many thanks to those who replied with help.

The 90deg bend is right behind the stove because it exits to the rear, so there is no choice.  At the moment it is running with a short extension from the stove (about 30cm) and then the 90deg bend - Matt
[/quote]

 

To save any more problems with your 90deg bend, have you considered replacing it with a tee closing the redundant (lower) end with a tampon and then you can remove the tampon for cleaning and flue sweeping? You might have a problem with tar residue collecting in the bottom, tampons are available with a small tube to allow drain off into a small tin or WHY.

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[quote user="retread"]

To save any more problems with your 90deg bend, have you considered replacing it with a tee closing the redundant (lower) end with a tampon and then you can remove the tampon for cleaning and flue sweeping? You might have a problem with tar residue collecting in the bottom, tampons are available with a small tube to allow drain off into a small tin or WHY.

[/quote]

Yeah, I did look at those T-pieces the other day, but our flu is 97mm and the smallest they had in the local place was 111mm.  What I'll probably do in the longer term is get an adapter

to take it from 97 mm to 125mm straight out the back of the stove and then put in one of those T-pieces in to give better flow.  The current bend is a folded one, and it obviously gives lots of ridges for tar etc. to get stuck.

Cheers,

Matt

Enjoying a toasty warm lounge again! (as are the cats!)

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