Tar leaking from flue of wood burning stove

[Robina]

Hi,

I posted a couple of years ago about tar leaking from the joints in the tubes of our wood burning stove. From a short stay in early November the problem seems now to be solved - no leakage in one week's fairly cold usage - Christmas will be a tougher test.

For information - there were other issues than those aired in the last thread.

We could not in the end have double skin insulation as the chimney is a) too narrow and b) an angle in it too acute for the flexibility of the necessary liner. Apparently this is not unusual in little old cottages.

The tubes rise out of the stove do a 90% bend into a boxy sort of chimney constructed on the wall which goes up into the loft and then it angles out into the original chimney inside the wall.

We thought to solve the problem by moving the stove immediately below the boxy chimney so doing away with the 90% bend. This apparently is deliberately there as a safety device to prevent tar running straight down into the fire - which can be dangerous.

The boxy chimney on the wall has a "well" of about four inches below the hole where the tubes fit in. This is there to catch the tar running down the chimney as condensation. It was completely full of dried up tar and when we lit the fire it melted and flowed down the tubes.

Once this was cleaned out the problem disappeared. You can buy tar traps and install them if needed although we did not as the existing trap works OK now we know about it!

I have also been advised by two separate professionals that the tubes MUST be male end up. This is because smoke will escape if they are the other way up.

Hope this information is of use.

Robina

[pachapapa]

[quote user="Robina"]Hi, I posted a couple of years ago about tar leaking from the joints in the tubes of our wood burning stove. From a short stay in early November the problem seems now to be solved - no leakage in one week's fairly cold usage - Christmas will be a tougher test. For information - there were other issues than those aired in the last thread. We could not in the end have double skin insulation as the chimney is a) too narrow and b) an angle in it too acute for the flexibility of the necessary liner. Apparently this is not unusual in little old cottages. The tubes rise out of the stove do a 90% bend into a boxy sort of chimney constructed on the wall which goes up into the loft and then it angles out into the original chimney inside the wall. We thought to solve the problem by moving the stove immediately below the boxy chimney so doing away with the 90% bend. This apparently is deliberately there as a safety device to prevent tar running straight down into the fire - which can be dangerous. The boxy chimney on the wall has a "well" of about four inches below the hole where the tubes fit in. This is there to catch the tar running down the chimney as condensation. It was completely full of dried up tar and when we lit the fire it melted and flowed down the tubes. Once this was cleaned out the problem disappeared. You can buy tar traps and install them if needed although we did not as the existing trap works OK now we know about it! I have also been advised by two separate professionals that the tubes MUST be male end up. This is because smoke will escape if they are the other way up. Hope this information is of use. Robina[/quote]

The two separate PROFESSIONALS are wrong; smoke will not escape as the natural ventilation pressure will cause the pressure in the flue to be less than the pressure in the surrounding conduit.

However if the male -female connections are poorly installed or of insufficient length then colder air from around the flue may be drawn into the flue as the pressure is less within the flue.

Whilst the combustion gases for the reasons stated above will not escape, the tars and rainwater running down the inside of the flue on the  diametric peripheral  surface will have a tendency to leak out of the flue. This will be most likely during actual burning of fuel on the portion of flue close to the stove due to the elevation of the temperature in that portion of the flue.

 

[Quillan]

Two other things that may have an effect. The type of wood burnt (pine for instance has a high level of tar) and how dry the wood is. Newer, unseasoned wood, will produce tar.

[Robina]

Hi,

Pachapappa your explanation sounds very convincing - so I am at a loss as to who has the right answer on this. It seemed obvious to me that they should be male end down but then it would not fit over the collar into the stove. The stove installer told me which way up they should be when it started leaking and I asked him to rectify it. Recently, with the work to correct it the architect also said it - unprompted by me - and the builder who came to estimate for the work also said it. So what is a poor non-expert supposed to believe?

At any rate, the problem seems to have been resolved with no major work required. So fingers crossed.

Cheers,

Robina

[pachapapa]

[quote user="Quillan"]Two other things that may have an effect. The type of wood burnt (pine for instance has a high level of tar) and how dry the wood is. Newer, unseasoned wood, will produce tar.[/quote]

Poplar..

...No tar...

.....Dries quickly.

[clarksinfrance]

ALWAYS female pointing upwards, and male downwards. No horizontal of more than 150mm. Your so called "Professionals" are WRONG! Never fit flexible liner direct to stove, must be a length of 1mm stainless steel or enamel tubing. You can buy adaptors to go from your stove exit to the flue. There are a myriad of other regulations, all are available on the internet if you search long and hard enough.

[pachapapa]

[:D][IMG]http://www.forum-chauffage.com/images/raccorder-insert-conduit-de-chemine-bv03.jpg[/IMG]

[AnOther]

I found this in the Poujoulat design guidelines which clearly infers female up.

'The joint between flues must be airtight (and if necessary pressure tight) and the joint between flue sections must be designed so that condensates run down inside the flue and not out of the joint'

That said the 'T' piece on my Godin is male up, as consequently is the rest of the flue, yet it does not suffer from any leaks of any sort but then the joints were made with fire cement. Have others sealed their joints or just slotted them together I wonder ?

[IMG]http://i127.photobucket.com/albums/p123/biskitboyo/flue.jpg[/IMG]

[marcardis]

Your T piece is fitted upside down.

All pipe joints MUST be female up.

With the rigid pipe this way up there is no safe way of attaching a flexible pipe above the register plate.

Marcardis

[marcardis]

The collar on the top/back of the stove is a female fitting.

The rigid flue pipe MUST fit inside this not over it.

Hopefully your architect is better informed on other building issues!

Marcardis

[AnOther]

[quote user="marcardis"]Your T piece is fitted upside down.[/quote]

I cannot see how that can be as the bottom is different and has a removable plate for cleaning so cannot possibly go any other way ?

[quote user="marcardis"]With the rigid pipe this way up there is no safe way of attaching a flexible pipe above the register plate.[/quote]

I have no flexible pipe. There is a very small crank of a couple of inches just above the register plate which I made myself by cutting and welding a straight piece, but otherwise the flue is straight and comprised simply of 3 1.5m sections similar to what is visible.

Architect ?

Edit: Incidentally the burner outlet is smooth and tapered lending itself perfectly to an outside fit whereas the inside is rough cast and would therefore be very difficult to seal. Also, if not for fitting as shown, what is the purpose of that particular design of 'T' piece ?

[Badger LX]

There are specific connectors for "raccord sur buse" i.e. connecting to the cast outlet of a poele etc. They have a specifically sized reduction which allows them to drop inside the outlet, which a standard male pipe end will not. Check out page 133 of the Poujoulat catalogue

This all allows you to keep the joints the right way up (male down/female up).

[AnOther]

I understand the adapter for the burner now but it still doesn't explain what my 'T' piece is for with it's female up end ?

It's moot anyhow as I can categorically assure you that it ain't getting changed now !

[Peter]

As a surveyor I often see flue pipes fitted upside down.  The female should be up so the tar flows back into the appliance where it will be safely burnt. The T sections pictured are not designed for wood burning appliances.  Flues should be lined all the way to the top.

If bends are needed, then no part of a flue pipe should form an angle greater than 45° from the vertical.

It is recommended that a vertical rise of at least 600mm should be allowed, immediately above the appliance before any change of direction.

P

[master of none]

How is this resolved when fitting a stove with a rear exiting flue?

[Peter]

a burner with a rear flue requires this sort of adaptor

http://www.charnwood.com/features-flue-adaptor.asp

P

[AnOther]

I could probably fit such a thing to my Godin (I'm not going to!) but it begs the question if what is supplied as standard (see my photo) is completely wrong why do they sell it with that fitted ?

[master of none]

Thanks Peter.

[pachapapa]

The middle bit of the "tee" sticks in the Godin, the female bit sticks up and the male bit sticks down. The tars are collected from the male bit by regular removal of the female cap.

Unfortunately yours is installed incorrectly.[:-))]

[IMG]http://www.godin.fr/components/com_virtuemart/shop_image/product/KIT_TUYAUX_4cadddd792893.jpg[/IMG]

[just john]

My rear exit Godin has been installed with 130mm inox, the original flange (brown enamel) has been damaged but refitted, so looking to reinstall this I am struggling to find any 130mm flue pipe, let alone enamel or a nice enamelled flange, does anyone have any suggestions where I can obtain either of these?

[pachapapa]

[quote user="just john "]My rear exit Godin has been installed with 130mm inox, the original flange (brown enamel) has been damaged but refitted, so looking to reinstall this I am struggling to find any 130mm flue pipe, let alone enamel or a nice enamelled flange, does anyone have any suggestions where I can obtain either of these?[/quote]

The picture above is lifted from the components section of the...wait for it....the Godin catalogue.

http://www.godin.fr/components/com_virtuemart/shop_image/product/KIT_TUYAUX_4cadddd792893.jpg

They claim to do them in lots of pretty colours.

[AnOther]

I muat admit that I'm still confused.

If you take another look at my Godin the cast iron connector exiting from the rear is exactly what it was supplied with and it is both smooth and slightly tapered offering an obvious and perfect push fit for the female 'T' piece fitted to it. Having had to once take it off to move the burner to do some work on the base it stands on I can assure you it is a VERY tight fit and does not leak in the slightest.

As I said previously the inside of the connector is rough and completely unsuitable for a pipe or connector male end to be inserted into so if it is 'wrong' I ask again why have they supplied it like that what is that 'T' supposed to fit on as whatever it is it will always be male up. Are the rules for pipe orientation different for different fuels? It is a multifuel burner BTW.

Furthermore you will note that the female entry to the 'T' piece which is fitted is parallel and not a female in the same sense as the section of pipe connected to the top of it for instance so clearly is not intended to have a normal male inserted. When I installed it I had noted that the flue pipe had labels on indicating female up but I could find no 'T' adapter to allow this hence I had no option but to fit them upside down but firmly cemented.

[img]http://i127.photobucket.com/albums/p123/biskitboyo/flue.jpg[/img]

[AnOther]

I muat admit that I'm still confused.

If you take another look at my Godin the cast iron connector exiting from the rear is exactly what it was supplied with and it is both smooth and slightly tapered offering an obvious and perfect push fit for the female 'T' piece fitted to it. Having had to once take it off to move the burner to do some work on the base it stands on I can assure you it is a VERY tight fit and does not leak in the slightest.

As I said previously the inside of the connector is rough and completely unsuitable for a pipe or connector male end to be inserted into so if it is 'wrong' I ask again why have they supplied it like that what is that 'T' supposed to fit on as whatever it is it will always be male up. Are the rules for pipe orientation different for different fuels? It is a multifuel burner BTW.

Furthermore you will note that the female entry to the 'T' piece which is fitted is parallel and not a female in the same sense as the section of pipe connected to the top of it for instance so clearly is not intended to have a normal male inserted. When I installed it I had noted that the flue pipe had labels on indicating female up but I could find no 'T' adapter to allow this hence I had no option but to fit them upside down but firmly cemented.

[IMG]http://i127.photobucket.com/albums/p123/biskitboyo/flue.jpg[/IMG]

[just john]

My set up looks similar to yours Ern, rear entry Godin, fitted with an inox flue on the outside of the Godin flue, the flue is however female up and male down, it was also fitted with sealant and as yet suffers no leaks. I would like to change it to enamel if possible, could you tell me what size your is?, and where you got the enamel flue?

 

[AnOther]

It's 125mm as I recall and all items were obtained at Brico Depot in Montauban, it's the only place I have seen black enamel which is what I wanted to complement the burner.

They had similar in stock only about a week ago.