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Cautionary Tale - Check you fires, check you flues


EdwardMeades

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EDIT - I should add for complete transparency and honesty. I had changed the stove and collar myself last year myself. This was clearly an issue caused by me and my own carelessness. I am ashamed to admit it of myself but the message is important.

 

I want to share my fire scare with the community. Like a lot of people who have bought boats over the last couple of years, I bought mine cheap with an owners fit out. It has a recent BSS and everything looked OK on the Survey. There must be so many other people out there who, like me, are careless, naïve, and not aware of how quickly things can go wrong. If you have recently bought a boat or not familiar with fire safety and the regulations houses and boats I urge you to read on. 

 

I think there is a real risk for others who have bought boats with owner fit outs, that have had fires installed by people who do not know what they are doing and do not understand the dangers. 

If you have never sat down and thought about what could go wrong, planned how you could deal with a fire and, more importantly, how you can get out quickly I really implore you to do so - it will only take you a few minutes and it could save your life.

 

My Flue is single skin, all the way up through the ceiling. Where the flue passes the tongue and groove cladding and into the chimney collar it had a decorative metal register plate on, to hide the hole. The register plate was then screwed into the wood and the gaps caulked. (register plate looked something like this). This register plate was MUCH too close to the flue. It was not touching the flue but had been installed off centre. At the closest point the flue was approx. 10mm from the plate. The heat was transferred from this into the tongue and groove. Over time the heat transferred had charred the wood . There was no visible charring or discolouration around the register plate. It only occurred directly under it to the front of the flue.

 

A few weeks ago we had some really strong winds. The fire was on and I took the dog out on the towpath. I noticed a smoke blowing from a mushroom vent near to the chimney. This immediately sparked panic - there were no joins in the flue inside the ceiling, and no smoke was inside the boat. I realised that there must be something on fire, inside the ceiling. 

I removed the register plate as quickly as I could - and saw a small area in front of the flue was charred and glowing orange with embers. Now that I had exposed the area to oxygen, it immediately caught fire (See Pyrolysis). The wind was also blowing in through the mushroom vent and feeding the flames. I grabbed my fire extinguisher and put the flames out, and also sprayed the area with water to take the heat out of it.

 

This was really a scary experience and I am extremely lucky:

- It was complete chance that I noticed the smoke coming out of the mushroom vent whilst outside

- The Fire Extinguisher was close to hand BUT IT WAS OUT OF DATE BY 1 YEAR!!!

- The event happened at 7pm. If I had been asleep I probably would not have noticed

 

What have I done to prevent this happening again?

- I have cut the wood back from the flue much further (200mm all around)

- Removed the single skin flue and replaced with twin wall

- No metal register plate. I am just leaving the hole for now for my own piece of mind. I am considering making a cover with a generous clearance all around out of a material with poor conductivity like cement board.

- New fire extinguishers, one at the front of the boat and one at the back

- Emergency hammer to break a window (just in case)

- Read as much literature on fire regulations for boats and houses as I can stomach

- Read the MAIB report for the Lindy Lou 

 

 

 

 

 

Flue.jpg

Edited by EdwardMeades
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The London whitewash on the timber didn't help either. I don't think I have ever got the top of the flue hot enough to do that. The cast iron collar, originally used on wooden cabins, acts as a heat sink - - - hopefully.

 

There is another danger point I have come across this winter relating to Morso Squirrel stoves with back boilers.

 When you sweep the chimney, the soot and clinker falls onto the top of the back boiler restricting the throat of the flue. If you don't clear this after sweeping it can build up and set hard like concrete, severely choking the flue and risking CO fumes into the boat.

Have a look with a torch inside your Squirrel stove today before it kills you.

I suppose that without a back boiler this can still happen with the baffle plate but that is removable so easier to sort out.

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I doubt it...most people have enough common sense to realize the hot flue must be separated from flammable materials,and the traditional way is an outer skin with air space,and air flow to cool the installation.........there is certainly no harm in a weather excluder around the outer skin......Similarly ,there must be airspace between brick bases for stoves and any wooden floor underneath,as the bricks will heat up with time.

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Part of the problem is the flue, it is a thin single skinned flue and not a cast or double skinned one. When the stove is on I can touch my cast stovepipe at the top something that is not possible to do with a thin wall pipe without losing skin.

I would change it to a cast one, As I don't like the aesthetics of  double skinned flues.

 

 

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9 minutes ago, Tracy D'arth said:

When you sweep the chimney, the soot and clinker falls onto the top of the back boiler restricting the throat of the flue. If you don't clear this after sweeping it can build up and set hard like concrete, severely choking the flue and risking CO fumes into the boat.

That is why I used  the rear flue entry on our Squirrel.  The base of the flue and rear of the boiler can then be accessed through the top entry.  I find the top lid will seal happily onto  stove rope under it's own weight, but you can use  fasteners as well if wished. These cam be got at through the front fairly easily.

 

The bonus is that you can get a bigger kettle on top.

 

N

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1 hour ago, Loddon said:

Part of the problem is the flue, it is a thin single skinned flue

 

I have to say, this struck me too. That flue material looks odd, like a cheap external thin steel chimney cobbled to fit. Not the 1/8" wall thickness flue tube sold by chandlers for the job. 

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16 minutes ago, MtB said:

 

I have to say, this struck me too. That flue material looks odd, like a cheap external thin steel chimney cobbled to fit. Not the 1/8" wall thickness flue tube sold by chandlers for the job. 

 

It is a single skin flue that would be used for a house - I think it is 1.2mm thickness.

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1 minute ago, EdwardMeades said:

 

It is a single skin flue that would be used for a house - I think it is 1.2mm thickness.

 

There you go - thats the reason it got too hot.

Use proper boat stuff (about 3-4mm) when doing boat jobs and use 'house stuff' for doing house jobs (that applies to everything, not just stove flues)

 

Don't cut corners.

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22 minutes ago, Alan de Enfield said:

 

There you go - thats the reason it got too hot.

Use proper boat stuff (about 3-4mm) when doing boat jobs and use 'house stuff' for doing house jobs (that applies to everything, not just stove flues)

 

Don't cut corners.

Totally agree with hindsight. I'm sure there are many others who make the same mistakes

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22 minutes ago, Alan de Enfield said:

 

There you go - thats the reason it got too hot.

Use proper boat stuff (about 3-4mm) when doing boat jobs and use 'house stuff' for doing house jobs (that applies to everything, not just stove flues)

 

Don't cut corners.

Steel is a reasonably good heat conductor, so a thicker flue doesn't run much cooler than a thin one, a double-wall flue is needed to make a big difference.

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2 hours ago, Loddon said:

Part of the problem is the flue, it is a thin single skinned flue and not a cast or double skinned one. When the stove is on I can touch my cast stovepipe at the top something that is not possible to do with a thin wall pipe without losing skin.

I would change it to a cast one, As I don't like the aesthetics of  double skinned flues.

 

 

Absolutely.  My cast iron flue never got that hot.  I would not use a stove with a flue like that.  (even if thousands of boaters use them every day without problems).

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49 minutes ago, IanD said:

Steel is a reasonably good heat conductor, so a thicker flue doesn't run much cooler than a thin one, a double-wall flue is needed to make a big difference.

I agree in theory but explain that to my stove flue then because it's obviously doing something wrong. I can put my hand on it without it searing the skin off my hand, If I had done that in the cottage with the same stove but a thin wall flue I would have lost layers of skin. Yes I did touch it once by mistake so know exactly how hot it gets.

 

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9 minutes ago, Loddon said:

I agree in theory but explain that to my stove flue then because it's obviously doing something wrong. I can put my hand on it without it searing the skin off my hand, If I had done that in the cottage with the same stove but a thin wall flue I would have lost layers of skin. Yes I did touch it once by mistake so know exactly how hot it gets.

 

I didn't say thickness made *no* difference, I said that if you want to make the flue a lot cooler it won't do the job and you need a double-walled one. I do thermal analyses as part of my job, and an extra couple of mm of steel thickness is not going to lower the surface temperature by much, because most of the thermal resistance (more than 90%) is between the outer flue surface and the air, not through the steel. It does increase the thermal mass so it will take the flue a lot longer to heat up (which might also explain what you've found), but eventually it'll get almost as hot as a thin one and burn you just as badly.

 

If your one in the cottage is so much hotter, maybe the reason is that you run the stove harder there to heat up a cottage instead of a boat, or for longer at maximum heat so the flue has more time to heat up?

Edited by IanD
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14 minutes ago, Loddon said:

I agree in theory but explain that to my stove flue then because it's obviously doing something wrong. I can put my hand on it without it searing the skin off my hand, If I had done that in the cottage with the same stove but a thin wall flue I would have lost layers of skin. Yes I did touch it once by mistake so know exactly how hot it gets.

 

 

Do you have a magnetic stove thermometer? It wouldn't take much effort to put this on your flue at the top and see how hot it actually gets - just to see it in numbers.

 

It's still something you should be wary of. My flue wasn't in contact with the wood, it was the register plate which was much thicker steel. That still got hot enough to cause the wood to combust. From memory I think the thermometer at the top of my flue reached 150 degrees.

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14 minutes ago, IanD said:

It does increase the thermal mass so it will take the flue a lot longer to heat up (which might also explain what you've found), but eventually it'll get almost as hot as a thin one and burn you just as badly

I think that with the stove being lit for a couple of months or so it should have got up to temperature. 😯

I'm not disagreeing with the theory just pointing out that  practice, as mentioned by others, doesn't always follow theory.

A twin wall is the safest solution but they are Fugly and impractical on a boat.

 

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26 minutes ago, IanD said:

If your one in the cottage is so much hotter, maybe the reason is that you run the stove harder there to heat up a cottage instead of a boat, or for longer at maximum heat so the flue has more time to heat up?

Both stoves were almost always on tickover or just above and both used to go on in November and off in March/April

Never been able to run a stove at maximum heat the room gets to hot.

There was another stove in the other room in the cottage also providing heat.

Only difference is the length of chimney/flue.

 

Edited by Loddon
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7 minutes ago, Loddon said:

I think that with the stove being lit for a couple of months or so it should have got up to temperature. 😯

I'm not disagreeing with the theory just pointing out that  practice, as mentioned by others, doesn't always follow theory.

A twin wall is the safest solution but they are Fugly and impractical on a boat.

 

 

That always means that you've forgotten to allow for something in the analysis (which happens all the time, I see this on a daily basis at work), not that theory is wrong -- the laws of thermodynamics aren't open to debate 😉

Edited by IanD
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11 minutes ago, Rickent said:

This is how I fitted my flue, the actual flue at the top is hot to the touch, but the collar is cold as is the wood around it.

Same as mine and many others with a proper chimney collar and not just a piece of pipe welded to the roof.

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7 minutes ago, Tony Brooks said:

and as said that collar acts as a heat sink, conducting heat from the top end the flue to a large area on the roof where the heat can dissipate.

...which will keep a thick flue cooler than a thin one, because the heat travels up the flue, through the collar and into the roof.

 

So theory and reality agree. Mr Kelvin would be very happy,as would Flanders and Swann... 😉

 

 

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Phew! that was indeed lucky. Note: It is important to keep a good distance between the flue and nearby woodwork too, a fire in boat that burned out a few years ago seemed to have started where the flue was close to the lining although it was hard to tell after the event. A friend could get a standing flame from his chimney with not much effort by opening the bottom of the stove and chucking some kindling on the fire, impressive but maybe not very sensible. Some rules and advice don't matter much but some do, fire safety really does. And thanks to the OP for the post.

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5 hours ago, EdwardMeades said:

 

Flue.jpg

 

1 hour ago, Rickent said:

 

20211201_142231.jpg

A comparison of those two pictures is instructive. In the second the wood lining is cut well back from the flue pipe, not so in the first. The OP blames the register plate for conducting heat into the wood, but I think the main cause was heat radiating directly from the flue pipe to the very close timber. The lining should have been cut much further back - as far as the register plate would allow, leaving just enough wood in the corners for the screws holding the register plate in place. And the gap between the flue and the edges of the timber should have been filled with fibreglass loft insulation. The large area of the register plate would dissipate heat to the air below, faster than it would transfer from the flue pipe at a single point of contact, meaning the register plate would stay relatively cool, and could not therefore transfer significant heat into the timber planking.

 

The OP's other points about the Lindy Lou report, having in-date fire extinguishers and thinking in advance about how you would escape are all very valid.

Edited by David Mack
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