Chimney Bricks: Thermal or Insulating?

[Marcel]

#49

(M) I'll be closing my dome tomorrow, if it doesn't rain, and want to start on my chimney. I will probably use neither a steel nor a clay liner.

(M) My question is, given a builder's choice is to use only brick for a flue-chimney, would it be better to use insulating brick or firebrick? ___

(M) I can see advantages to both but those plusses are predicated on assumptions of whether stored chimney heat will help maintain dome heat, or whether a chimney inherently gives up heat with the smoke.



(M) Thanks to anyone how contributes their perspective. If you see a post which refutes your position, pipe in anyway. I'll tally the thermals and the insulators.

Ciao,

Marcel

[Les]

I haven't built mine yet so this may be way off. If you think about it, by time the heat gets to the vent/chimney, the heat is pretty much gone from the dome. With that said, I would think you can use standard core brick. I am leaning in this direction myself. Anyway, that is my opinion and I respect it. :-)

Les...

[dmun]

I'd go with the firebrick. Insulating brick is soft, porous and will have a tendency to accumulate grease and soot. It could be damaged with a flue-cleaning brush if that were needed.

Firebrick, even half thick "splits" should keep your smoke contained. I wouldn't worry too much about heat loss at this point: If it cools off here it shouldn't draw down the heat from the dome. In any event, I suspect the whole unit will be insulated with your pearlite concrete, or whatever.

Building code is unyielding on this point: Refractory liner + half inch airspace + 4 inches of masonry, or a manfactured chimney. I suspect code is predicated on a chimney fire happening at the same time as an earthquake. I don't think this applies to freestanding ovens, but common sense does.

Good luck, David

[Marcel]

#49


(M) Les wrote:

(L) <snip> "If you think about it, by time the heat gets to the vent/chimney, the heat is pretty much gone from the dome."

(M) And, if you don't think about it, the heat is pretty much gone, too

(L) "With that said, I would think you can use standard core brick."

(M) If by "standard core" you mean either red brick or the firebrick I used for my cooking floor, I'm inclined to lean in your direction.

(L) "I am leaning in this direction myself. Anyway, that is my opinion and I respect it. :-)"

(M) Anyway, that's your story and you're stuck with it!


Les...

(M) Demon seems to agree with you. Here's part of his post:


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(Dmun) "I'd go with the firebrick. Insulating brick is soft, porous and will have a tendency to accumulate grease and soot ... <snip>

(Dmun) <snip> I suspect the whole unit will be insulated with your pearlite concrete, or whatever.

(M) I had not considered insulating the chimney, for decorative reasons, David. But I made a few dry set ups and everything I set up for that 18" slot seems wide and massive, probably because I can't picture the gable house around the igloo yet. I've seen your exquisite design work on Arcadian Clocks so I know that although form needs to follow function, there are times when both can be met.

(Dmun) Building code is unyielding on this point: Refractory liner + half inch airspace + 4 inches of masonry, or a manfactured chimney. I suspect code is predicated on a chimney fire happening at the same time as an earthquake. I don't think this applies to freestanding ovens, but common sense does.

(M) Nor, probably to outdoor ovens. I remember masonry BBQs from my youth which violated every existing code for indoor fireplaces.

Good luck, David"

(M) Thank you, David. At this point there is a 2-0 vote in support of the harder brick and I think I'll go with that, but, .... now that I've rediscovered 8"x8" clay liners locally in 1 foot heights (for only about $5 a section) I'm feeling less committed to the brick as I could insulated those liners quite easily. Also, their weight, even insulated will be so much less than the firebrick. Oh well, at this point luck will have to line up behind expediency. Thanks, Les and David for your input.
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(M) I will post another image on Forno Bravo's Photo Forum that shows what happens when vanes are badly cut. I really will need to fudge a lot of mortar to accomodate the uneven height of rings of brick. I think my cutting error was exacerbated by crossing over the opening throat too late. I had already gone higher than the flat iron. But, if I gable this "turkey" no one but you who read this will know of my error.