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Daniël Bos

Chimney fire causes?

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5 minutes ago, Peasgood said:

@renewablejohn had problems with his ESSE IIRC.

He's not been logged in for nearly two months now, fingers crossed he reads this

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46 minutes ago, Rough Hewn said:

Prevailing wind direction?
Does it work better on a still or windy day?
Have you tried burning kindling for an hour to heat the whole chimney, Increasing airflow?

wind direction or strength doesn't seem to make much difference.

Not tried just burning kindling, but i'd have thought if it was a draw issue like that it would eventually remedy itself after burning for hours?

It doesn't change whether it's just lit or going for hours/days. 

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1 hour ago, Daniël Bos said:

I suppose my main question is: can a badly controlled back boiler reduce the firebox temperature so much as to have caused this?

 

 

I think so; the reason being that to burn wood cleanly you need a flame. That flame needs time to completely burn the gases given off by the heat. The oxygen from the air has to diffuse into these gases and it burns the lighter hydrogen fractions off first. The yellow you see in the flame is the remaining heavier carbon compounds glowing in the flame. As long as they have enough dwell time in the flame they too burn out but if they touch a cold surface first  they don't and remain as sooty particles which then combine with any tarry vapours and congeal onto the flue further up. Once this layer gets thick enough and the fire is roaring it burns in the excess air, often with a blue flame in the chimney top  as carbon monoxide is generated and catches when it reaches fresh air.

 

Main way of preventing this is to burn hot and fast and not overload the fire. Never shut it down to smoulder but only when only a char bed remains

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I would say it is a flue problem rather than just the boilers cooling the fire, if you have all the air open and maybe the bottom door it should really take off and roar even when just lit.

My wood burner has insulated flue but the bit at the top where it is in the chimney pot gets tarred up no matter how hot I run it, I go up on the roof every 6 months or so and just scrape out the top metre.

You should not have smoke coming back into the room when you open the door.

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I had two or three minor chimney fires when I had a Rayburn years ago and the contributory factors were:

 

* Coal, and the associated soot build up

 

* Lack of a thermostat controlling water flow to the water jacket, meaning that on occasion the firebox would be cooled excessively

 

* Overfiring of the Rayburn, albeit only for a few moments. If the flue had become sooty due to the above two issues, leaving the vents open for even a fraction too long (so just too hot on the flue thermometer) would result in a chimney fire. It was easy to put it out with shutting the vents though

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