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Carbon monoxide build-up when burning smokeless coal but not wood


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Hi all,

 

Hopefully this post belongs here, apologies if not.

 

We've got a Saltfire ST2 stove, which consistently sets off our CO alarms after an hour burning Excel/similar. Burning wood never causes a problem, though.

 

I assume this has to be because the wood fire is burning more fiercely, whereas the Excel fire is burning more slowly. Perhaps it's getting cold enough that the chimney draw is reduced?

 

The Excel nuggets are red hot, and there are some barely visible white/blue tongues of flame around them. So it's not just smouldering. I've got the bottom vent most of the way open, and the top vent slightly open.

 

I'm going to try changing the door seals, but if those were faulty, I assume the CO alarm would be triggering for a wood fire as well?

 

Advice much appreciated!

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Also where do you keep the hot ashes!! Two winters ago a young lady winter moored here directly in front of my boat and one night late She had doors open and alarm going off. I went round and could find nowt wrong with stove etc. Some time later we realised she had emptied ash into a bucket and left it inside next to the stove as she didnt want to go out late at night!!

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12 minutes ago, frangar said:

When did you last sweep the flue? Im not familiar with the stove but is there any baffle plate that might have a build up of soot etc on it that needs cleaning?

 

Good points. Both have supposedly been cleaned recently by the previous owner, but I should verify that myself. Do you think they can be the cause if it's fine when burning wood, though?

 

I guess maybe the coal's just cold enough to tip the balance in favour of CO build-up.

 

9 minutes ago, mrsmelly said:

fotos of inside and outside stove please. And flue. Are all flue jojns tight and sealed with envirograff or somett?

Will get photos tonight/tomorrow. Joints are sealed with glass rope. When burning a load of newspaper in the cold stove, the door seals emit a little smoke. No smoke from other joints, and no smoke from the door seals when adding paper during normal operation.

 

6 minutes ago, Tony Brooks said:

How close to the chimney is any open window? How long ha sit been doing it and if very recently which way relative to the flue and windows is the wind blowing and how strong?

Ohhh... this is a good point. We've got a mushroom vent quite close to the chimney. Another thing to try.

 

It's been doing it as long as we've been on the boat, but we only moved in a few weeks ago. The wind usually seemed to be going the other way to the vent, but I'll definitely add this to the mix of possible reasons.

 

2 minutes ago, mrsmelly said:

Also where do you keep the hot ashes!! Two winters ago a young lady winter moored here directly in front of my boat and one night late She had doors open and alarm going off. I went round and could find nowt wrong with stove etc. Some time later we realised she had emptied ash into a bucket and left it inside next to the stove as she didnt want to go out late at night!!

No doubt this is a common mistake, but it's not the problem here. We're not burning for long enough to have to empty the ashes - the CO alarm goes off after an hour or so.

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Check the flue pipe is not interally encrusted with solid cement like crud. Ordinary flue brushes won't shift it.  Petro oily fuels like Excel probably give off emissions similar to vehicle exhaust, ''pre catalyst'' so could be partly the trouble. You could plonk a washing up bowl over the vent to see if that stops it, or extend the chimney.

Edited by bizzard
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48 minutes ago, wordsalad said:

 .

 

It's been doing it as long as we've been on the boat, but we only moved in a few weeks ago. The wind usually seemed to be going the other way to the vent, but I'll definitely add this to the mix of possible reasons.

 

 

How many weeks ago, boat stoves need the chimneys swept much more than houses especially if they are run very low.

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35 minutes ago, bizzard said:

Check the flue pipe is not interally encrusted with solid cement like crud. Ordinary flue brushes won't shift it.  Petro oily fuels like Excel probably give off emissions similar to vehicle exhaust, ''pre catalyst'' so could be partly the trouble. You could plonk a washing up bowl over the vent to see if that stops it, or extend the chimney.

Yes the Rayburn on Anthracite is fairly closed down on wood its more open to keep it going neither sets off the smoke/carbon monoxide alarm but when smoke starts coming out when refueling I know it time to clean the chimney and I have those hard deposits it takes more than a brush to clean the chimney at least once a month

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1 hour ago, bizzard said:

Check the flue pipe is not interally encrusted with solid cement like crud.

Soon after our NB purchase we had the flues “professionally” swept. This included a chain flail driven by a cordless drill.

Later we discovered that the lower quarter of the flue was substantially reduced in diameter by a layer of the afore mentioned cement.  It had such a smooth and even finish that initially I assumed it was a double skinned flue at the bottom.

It took many difficult sessions with a homemade implement resembling a long medieval club to remove most of the offending “concrete”. I think that for many years, the lower section of the flue had escaped whatever cleaning was employed.

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1 minute ago, gbclive said:

Soon after our NB purchase we had the flues “professionally” swept. This included a chain flail driven by a cordless drill.

Later we discovered that the lower quarter of the flue was substantially reduced in diameter by a layer of the afore mentioned cement.  It had such a smooth and even finish that initially I assumed it was a double skinned flue at the bottom.

It took many difficult sessions with a homemade implement resembling a long medieval club to remove most of the offending “concrete”. I think that for many years, the lower section of the flue had escaped whatever cleaning was employed.

Yes. I had to modify a length of 3/4'' steel pipe by flattening one end like a chistle. ramming it up and down and turning it like an auger with stilsons. Best done cold of course, the crud will be more brittle and break away easier.

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3 hours ago, BWM said:

It would be worth reversing the air settings, less air at the bottom and the same or slightly more open at the top. 

I agree. I would be inclined to fully open the top damper and close down the bottom damper more.

Maybe there isn't enough low level ventilation in the boat or the door seals on the stove need replacing ?

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10 hours ago, PhilR said:

I agree. I would be inclined to fully open the top damper and close down the bottom damper more.

Maybe there isn't enough low level ventilation in the boat or the door seals on the stove need replacing ?

My guess is that the draw is the issue, the Epping range is just bits of cast iron plates resting on each other to create a hob. There are no seals and zero leakage if running properly but if you shove loads of air into the bottom with the top control shut...

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Thanks for the advice, all. I had a look today, and the chimney, flue and baffle haven't been cleaned - or if they have, it was a cursory job.

 

I've given it a preliminary attempt with a plumber's snake and broom handle + wire brush. Annoyingly, it turns out my stove's baffle plate is welded on, so I've not managed to clean as thoroughly as I'd want. Still, I dislodged a lot of muck.

 

I'll attempt another test Excel fire this evening with two CO monitors close at hand. If I'm still having problems, I'll remove the flue to get better access to flue and baffle.
 

Edited by wordsalad
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I'm not sure about the advice here re the air control settings. Wood burns with air from above, coal burns with air from beneath which passes up through it. Hence the advice in my stove's manual to close the top vent completely when burning coal and to use the bottom vent as the air supply (and vice-versa for wood); additionally it says to get the stove burning well on coal and then for a short while open the top vent to send a wash of air down inside the front door to clean the glass.

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46 minutes ago, Keeping Up said:

I'm not sure about the advice here re the air control settings. Wood burns with air from above, coal burns with air from beneath which passes up through it. Hence the advice in my stove's manual to close the top vent completely when burning coal and to use the bottom vent as the air supply (and vice-versa for wood); additionally it says to get the stove burning well on coal and then for a short while open the top vent to send a wash of air down inside the front door to clean the glass.

It depends where the top vent is. Generally, the vent below the grid  feeds solid fuel, above the grid but below the glass feeds wood, above the glass is airwash to help keep the glass clean. On both my woodburner at home and solid fuel aboard, "ticking over" needs only airwash, and even then not fully open. Any air from the bottom results in a brighter, hotter burn.

Edited by Sea Dog
Sp airwash
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I'd say the coal vs wood thing is a red herring. Somehow, somewhere combusted gases are escaping your stove into the cabin. If this was my stove I would stop using it IMMEDIATELY. CO is extremely dangerous and I can tell a story about a relative semi paralysed by it dragging his unconscious family outside (they fortunately survived) if that will encourage you.

 

Once I had stopped using ANY fuel in the stove the next thing I'd do is work out where the leaks are emanating. I keep smoke bombs for this purpose (available from chandleries). Any one of the rope seals could be the issue - the fact that smoke escapes the door suggests that that's the problem - I'd have replaced these on the strength of your newspaper test! Depending on the stove there might be seals in the actual body of the stove. It is expensive but necessary to recondition your stove and replace all of these seals eventually. I personally would blank off the mushroom vent that is near the chimney. Another possibly cheap/easy fix to improve the draw and get the exhaust further from the cabin is a longer chimney.

 

I'm not as experienced as the other posters who have replied and perhaps I'm more paranoid than they are, but I would not mess about with a stove. Test for leaks, replace all the ropes, block off any ventilation near the chimney, use a longer chimney, and yes clean the flue out regularly.

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Im not as experienced as the other posters who have replied and perhaps I'm more paranoid than they are

 

yes I'd say you are the op is clearly being prudent and even mentions having two CO alarms   

 

suggesting blocking off ventilators is dubious advice at best.

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29 minutes ago, jonathanA said:

Im not as experienced as the other posters who have replied and perhaps I'm more paranoid than they are

 

yes I'd say you are the op is clearly being prudent and even mentions having two CO alarms   

 

suggesting blocking off ventilators is dubious advice at best.

I don't think the advice is ventilators plural, just any one that may be close to the chimney.

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Our CO alarm went off last December for the first time ever!

The stove was also not really getting as hot as it did.

Took the chimney off and there virtually no hole left for the gas to go up the flue. Chipped it all out and it was then fine.

The fact the OP says he was running it with the bottom vent fully open says to me the flue is blocked. I am sure now that it has been cleaned, it all will be fine.

It is quite surprising how quickly flues can block up. I'm checking mine monthly now.

 

 

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