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Author Topic: What causes a chimney to smoke?  (Read 8419 times)
Bodidly
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« on: January 11, 2013, 05:40:57 PM »

I thought I new the answer to this but now I am not so sure. We have a Saey stove and we only burn dry logs on it. You get a bit of smoke when putting a new batch of logs on but once this is up to temperature the gases leaving the chimney are clear. Now the last few days I have been looking after the running of my parents Woodwarm. This I believe is a top stove and it is running on the same wood as we burn. I loaded it up got it blasting away and then set it to burn with a good flame licking around the firebox. I looked up at the chimney and there is a bit of smoke showing so go back in and check the stove but it was running fine. The only major difference I can think of is we have an insulated flue. Now I always thought if you run the stove right most of the particulates get burnt off and the gases are clear and that the reason for an insulated flue was just to help with the draw but maybe there is more going on. What are your thoughts on this?
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Bodidly
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« Reply #1 on: January 13, 2013, 07:14:41 AM »

100 views but no ideas?
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biff
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« Reply #2 on: January 13, 2013, 08:12:34 AM »

Yo Beau,
        Good Sunday morn to you.Its a difficult one to answer.There are all kinds of different things at work,Different temperture,different moisture content, different chemical contents of the wood,perhaps the chimney is sooted up where you cannot see it.
     Maybe the stove does not get up to running temperture long enough.Perhaps if you kept it running non stop for 48 hours at a very high temperture then maybe it might clear out all the carbon deposites in the chimney and stove.
  I guess you can only experiment untill you find the answer.On the other hand,you will always get a certain amount of smoke when you light a fire,its natural.Is it possible that rain is falling down the chimney and damping the regulator bends,then turning to steam as it mixs with the hot fumes,?
                                               Biff
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Countrypaul
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« Reply #3 on: January 13, 2013, 08:38:39 AM »

What colour is the smoke? The whiter it is the more steam there is likely to be in it. If the non-insulated flue is cooling the exhaust gases then the water might condense out as steam more easily giving the impression of more smoke.

If the smoke if black or blue then there are highly likely to be particulates in it from incomplete combustion.

As Biff says, there can be many different causes and very difficult to pin down, try Biff's suggestion would be my approach.

Paul
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Bodidly
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« Reply #4 on: January 13, 2013, 09:51:39 AM »

"water might condense out as steam more easily giving the impression of more smoke. " that does sound possible nice one Smiley

It is possible that as Biff suggests there are sooty deposits in the flue and these are taking a while to burn off but I am pretty sure we are getting good combustion. It may be just this as have just got back for a walk having stoked both fires up. I went to take pictures of both chimneys and their respective smoke outputs and found things looking much better than a few day ago. I should have gone to do this before re posting this morning  Embarrassed

Thanks
Beau
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ecogeorge
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« Reply #5 on: January 13, 2013, 10:18:33 AM »

Does this stove have a boiler ? is cold water dragging the combustion temp down?
rgds George.
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Bodidly
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« Reply #6 on: January 13, 2013, 10:57:42 AM »

Does this stove have a boiler ? is cold water dragging the combustion temp down?
rgds George.

No boiler on either. If problem shows again I have camera at the ready so you guys can see  Smiley
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Justme
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« Reply #7 on: January 13, 2013, 04:46:29 PM »

What about differing external climatic conditions?
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renewablejohn
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« Reply #8 on: January 13, 2013, 09:50:00 PM »

Just had a quick look at Woodwarm specs below. Surprised to see max burn temp 400C could it be your trying to burn at to high a temperature for the stove and therefore not getting complete combustion.

http://www.woodwarmstoves.co.uk/_assets/manuals/new%20instructions%20fireview%20march%202010.pdf
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Bodidly
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« Reply #9 on: January 14, 2013, 06:47:38 AM »

Is this likely? I always thought the hotter the burn the cleaner the burn.
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renewablejohn
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« Reply #10 on: January 14, 2013, 09:21:28 AM »

Is this likely? I always thought the hotter the burn the cleaner the burn.

Which is why I made the comment about the 400C max burn temperature. As a comparison my Dunsley Yorkshire works upto 1100C. I presume at 400C your not getting full combustion or secondary burn to burn the smoke.
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Bodidly
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« Reply #11 on: January 14, 2013, 09:23:15 AM »

Sorry John
I misread your previous post.
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renewablejohn
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« Reply #12 on: January 14, 2013, 09:32:38 AM »

Have you tried reducing the draw up the chimney. Going through the woodwarm manual it would appear chimney draw is critical with to much draw being more of a problem for this stove then having to little draw. ie slower draw more complete burn. I must admit I have never seen such complicated instructions just to set the right level of air control.
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wattever
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« Reply #13 on: January 14, 2013, 02:55:21 PM »

Hi Beau,
My opinion, for what it is worth, is that you do not have a problem and that the "smoke" that you can see is mainly water droplets. The best way to check is to watch the plume leaving the top of the chimney. If it is water droplets produced from condensing water vapour in the flue gases, then it will evaporate within a few feet or yards, depending on the temperature, humidity and wind speed of the air passing the top of the chimney. The remaining bit of the plume will be the true smoke, i.e. unburnt solid particulates. This is normal and is particularly noticeable in this cold, drizzly weather.
Even dry wood is about 20% water and this must be driven off as water vapour up the flue. There is also water vapour produced from the burning of hydrogen from the molecular structure of the wood, but not much.
When a wood stove is lit or new wood is added, the wood starts to gasify and the burning gas heats the wood. This drives off the water before the primary combustion of the carbon can really set in. All this water vapour is invisible in the stove, but as it travels up the flue, it will start to condense as it cools. If it has not condensed by the time it reaches the external cold air, it will then, and then it will be visible as water droplets. Once this phase is over, very little "smoke" can be seen leaving the flue until the next charge of fresh wood.
The effect of an insulated flue will be to prevent the condensation within the flue itself to some extent.

wattever
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Bodidly
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« Reply #14 on: January 14, 2013, 03:24:21 PM »

Thanks for the reply's

I am not worried as such just interested in the difference between the two installs and surprised that the smoke is from the Woodwarm which I thought was the better of the two stoves.

I have tried to post some pictures of the smoke but the file size from my new camera is to large. How do I shrink these down and keep it simple as I am a bit dumb when comes to computer and cameras  Smiley
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