Clay chimney flue

[balon]

I’m nearing the end of the dome construction and was planning to add a metal flue and plate to the chimney. That was until my neighbour dropped off an old clay chimney pot which was lying idle in his folk’s place for many years. It’s really heavy and solid and I’m wondering whether it’s a good idea to consider it and the best way to install it. Any thoughts would be welcome. Some pics attached.

[balon]

Sorry don’t know why the picture loaded sideways

[angelboy]

I have a clay chimney that I want to use as well, so I'm interested in what your responses will be.

[david s]

It is highly likely to crack. I presume it is fired clay, but its colour and texture look more like cast concrete than fired clay. Clay chimney pots are used at the top of chimneys where they're not subjected to direct flame impingement so are relatively free from the risk of cracking. However lower down, closer to the fire, the interior surface gets way hotter. If the outer surface is in ambient air the difference between the inside surface and the outside surface (and therefore also the difference in thermal expansion) creates so much stress that it cracks the clay because of the thermal shock. Even an uninsulated clay flue tile does the same thing. There is a very good youtube video somewhere that demonstrates this. The remedy is to insulate around the chimney pot and this will prevent it from cracking.

[david s]

check this out

https://www.youtube.com/watch?v=bxOkwQyY-2w

[angelboy]

I was planning to build a few course (3-5) on the top of the arch then put the clay chimney. There won't be a direct fire going into it.

[david s]

Ok, you might get away with it then. Build it and report back about how it performs, but also be aware that placing extra high mass on top of the arch places extra sideways thrust on an unbutressed arch that already has its integrity compromised by continual thermal cycling and its associated expansion and contraction.

[fox]

That looks like a standard interlocking chimney flue section, just as David points out it is not designed for high heat and would normally be surround with concrete.
if it is big enough you could insulate the inside with ceramic fibre matting but personally I would use a twin wall stainless steel chimney.

[balon]

Thanks for the insights guys. Much appreciated. I think I will stick to the original plan