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Cast core vs. Refractory brick core – and cast heat riser vs brick heat riser  RSS feed

 
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Cast core vs. Refractory brick core – and cast heat riser vs brick heat riser

Hello everyone, I have uncertainty which bothers me a lot .
After three RMH's I've built, I still didn't decide for myself – which one is better – cast (perlite-cement 1:10) core or standard refractory brick core? First I made 7'' brick core and it worked fine, two seasons. Then I started thinking that I have too much ash, and that I could have higher temperatures and better usability of fuel (wood) with cast core. First RMH brick core was isolated with dry perlite around and 8cm ytong(porocement) underneath. Second, cast core of 8'' is made od 2cm thick refractoy plates, and insulation is 5-6cm perlitcement, and around rockwool. Underneath is 8cm perlitcement. Stove works fine.
I haven't made measuring, I rely here on pure subjective experience. I've tried to measure it but barrel was shiny and we could't get consequent results.
I think temperature is little bit higher with new heater, amount of ashes is similar, but I don't feel there is drastic improvement. Also, as I read in books and hear some experiences  - people say it is enough only few hour per day of burning, and that they have some abnormal temperature on the barrel (1300° F of higher). I have two floors (heat goes upward through the staircase) little bit less than 40m2 (430sq feet), styrofoam insulation 8cm, 25cm on the attic, but windows aren't high quality (they are some 'insulation' but old, wooden).
Ah – first heat riser was steel tube with perlit around, now I have pure cast perlitcement heat riser.
I was somehow happier with classic brick core, I felt it better, wtih this plates I'm sometimes scared it will break (one is damaged), I have to be careful when I put wood inside, and result isn't so dratically better. And, of course, I have lost cca 300 kg of thrmal mass.
I have idea to make brick core with bridge of insulated firebrick (white ones), pure dry perlit around. And I'm not sure about the riser – is better cast riser as I have now, or should I make riser of 1'' refractory plates (as in book of E&E). Or, if square riser is better, is it maybe better to make cast square heat riser?
I'm in this uncertainty a lot, and don't have the answer. Here are picture of first and second unfinished cores.

Thanks,
Jacob

HAB_1129.JPG
[Thumbnail for HAB_1129.JPG]
second, cast core (inside goes perlit-cement)
HAB_7254.JPG
[Thumbnail for HAB_7254.JPG]
first brick core (around goes pure perlite)
 
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You might want to look at ceramic fibre board.
I am just getting the materials together to build a new j tube, I will be casting the fire box from one inch refactory and building the tunnel and riser from the board.
I will also use the board to insulate the outside of the fire box.
 
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Hi Jacob;
When I had an 8"  cast J tube core and a cast riser , I regularly had barrel top temps of 1100F  But no higher.   1300 F sounds like a batchbox  design rather than a J tube.

I replaced my cast core after the first season, because (like yours) the feed tube was too fragile.  I was constantly trying to patch it.
I replaced it with an all heavy firebrick core . Now I can get +1000 F on the barrel top...only if I baby it with small wood. It regularly runs around 800 F.
My fireclay / perlite cast riser I have continued to use on my studio / greenhouse rmh.  I am planning on replacing it next season with a five minute riser made from stove pipe and ceramic fiber blanket.

As Fox suggested ceramic fiber board/blanket is the newest best product's to build your rmh from. The downside is that it costs a whole lot more than clay and perlite.

I am currently building a J tube with ceramic boards and a riser with ceramic blanket.  I have high expectations from these build materials, I expect the extra costs involved to be balanced out by the superior performance from them. It added over $300 to the build cost.

These products may not be available in your area....   If that is the case, then building your burn tunnel with insulated bricks is an excellent idea. If you have enough, then build your riser from insinuative bricks as well.  Use the heavy firebrick to build your feed tube. Split heavy brick would be even better.
 
Jacob Silver
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thomas rubino wrote:Hi Jacob;
When I had an 8"  cast J tube core and a cast riser , I regularly had barrel top temps of 1100F  But no higher.   1300 F sounds like a batchbox  design rather than a J tube.

I replaced my cast core after the first season, because (like yours) the feed tube was too fragile.  I was constantly trying to patch it.
I replaced it with an all heavy firebrick core . Now I can get +1000 F on the barrel top...only if I baby it with small wood. It regularly runs around 800 F.
My fireclay / perlite cast riser I have continued to use on my studio / greenhouse rmh.  I am planning on replacing it next season with a five minute riser made from stove pipe and ceramic fiber blanket.

As Fox suggested ceramic fiber board/blanket is the newest best product's to build your rmh from. The downside is that it costs a whole lot more than clay and perlite.

I am currently building a J tube with ceramic boards and a riser with ceramic blanket.  I have high expectations from these build materials, I expect the extra costs involved to be balanced out by the superior performance from them. It added over $300 to the build cost.

These products may not be available in your area....   If that is the case, then building your burn tunnel with insulated bricks is an excellent idea. If you have enough, then build your riser from insinuative bricks as well.  Use the heavy firebrick to build your feed tube. Split heavy brick would be even better.


Fox and Thomas, thank you a lot for answers! Now I feel better :). Here I can find ceramic wool, which us enormous expensive because it sells in 30m rolls. Maybe I can find some rests. There'no boards here, for now. Are these boards fragile? I mean -  can I build whole tunnel, or only the bridge? Now you gave me some more things to think of :). I can buy insulating refractory bricks.
One more question - do stovepipe - no matter which type of insulation - 'steal' some heat? Or, maybe it us the same if it gets very hot?
 
Fox James
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The ceramic board I have is quite tough but it is possible to dent or nick with you finger nail so I will not be useing it for any high abrasion areas.
I have both high mass and low mass risers that I have tested, both work very well but in different ways.
The high mass is made from 1” castable refactory with 2” of ceramic fibre  insulation, it takes a full two hours to get really hot but then stays very stable and is not really effected by the type or size of wood, it just eats anything including logs !
The low mass is just 2” of ceramic fibre inside a thin wall stainless tube, it heats up real fast and produces a lot of heat but it needs feeding and goes off the boil if not attended to.
If you have insulated bricks then I think they would be great to use.
 
thomas rubino
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Jacob;
The cf boards I used are stout but you can damage them if not careful, the exposed edges are fragile.  They can be used for the entire burn tunnel. They would also work to use as a riser .
I have been told that after firing they become much tougher.
If you have easy access to insulated fire bricks.  I would build with them, from the start of the burn tunnel to the top of the riser . Use the heavy bricks only in the feed tube. If you can source ceramic wool at a good price then use it for your riser.
 
Jacob Silver
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Sorry for late answer, I couldn't reply for a weekend. Now everything is clear for me. I'm still searching for ceramic boards, for now there aren't on our market yet. We have ceramic wool and refractory insulated bricks - they call them 'porit' bricks. I believe that CF boards are much better insulator than porit bricks, so I'll try to purchase ceramic boards. I fI will demolish this and build new, I will put best materials.
Thanks a lot for your help, Fox and Thomas, I am a little bit out of RMH trends in material and building, this was fast response for my needs .
 
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Jackob, i think your porit bricks, are not insulating firebricks, but air entrained concrete, which cracks everywhere, under intense heat.
 
Jacob Silver
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Satamax Antone wrote:Jackob, i think your porit bricks, are not insulating firebricks, but air entrained concrete, which cracks everywhere, under intense heat.



The name 'porit' associates on aerated concrete, but it isn't. These bricks are for building industrial stoves, and company for refractory materials sells them.
 
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