heat riser material choice

[canyon]

Try finding a plumbing/boiler maintenance contractor who cares and uses a quality stack like Excel. You might be able to get some sections that they are replacing with a different size for a different boiler.

[rocket_richard]

I'm hoping to cast a heat riser (the whole J tube) in several pieces.

I've bought a pricey bag of hi-cast cement (+$1/lb) rated to 2700ºF. I think this stuff will end up very strong and durable, but I'm concerned it's not as insulative as firebrick or refractory. I think too much dense material like concrete is not a good thing.

I plan on either casting quite thin, a 1" or thinner heat riser, but thicker where the wood is loaded, or finding a way to make a more isulative mix. Either way I'll be insulating with pearlite around the whole deal.

Donkey, what material is your heat riser? Is it very low density, like firebrick, or more like plaster or concrete?

Any mix recipes using the hi-cast cement I've got?

Rich

Update: I've found all kinds of recipes on home made foundry websites. It calls for a mix of refractory cement and pearlite. Seems like I've got everything I need to start experimenting.

[Donkey]

I've built the stove in my home using high temp castable cement. It works great! It's insulated all round in pearlite.
In my limited experience with the stuff, I find it pretty fragile. Less than an inch (or so) seems a bit thin. Try it though first and see. It may be prudent to make a smallish, thin piece and test it to gauge it's strength.
Granted, once the thing is in the stove it's very unlikely that it receive any physical blows.. Still, better to just test a little of the stuff before you commit too much $$.

Oh.. I just made a major goof with the stuff that I've been meaning to start a thread with here.
In a nutshell; I've created a mold using a wooden inner male part for casting tapered risers.. I thought that leftover, latex house paint would be enough to keep the refractory cement from sticking. Boy, was I wrong! I had to bash the thing to pieces to get it out again. Next time I'll probably wrap the thing with saran or some such thing first.

[roy]

could you construct the stove from stove pipe and then incase it in a thick layer of refactory cement and then as the flue burns away then you are left with a nice J shaped rocket stove?
or cheaper to use cardboard template for the whole thing.

can you add fine sawdust to the cement so it forms air spaces when it burns away? which would mean you use less cement?

[Donkey]

I've been considering the cardboard form/homemade refractory thing.. why the heck not??
Embedding stovepipe in refractory is a fine idea as well.

[mizwiz]

We've used metalbestos in wokrshops, it seems to work great for demos, but the inner steel sleeve sometimes warps or buckles over time. Might depend on stove size and heat.

We currently tend to do an inner & outer metal pipe - the toughest steel or iron we can find for the inner one - and create spacers, and fill in between with perlite. Perlite's "give" allows a little expansion without the metal liner needing to crawl out of its cage.

Ianto said last January he prefers brick for longevity.

-Erica Wisner
some pix available at picasaweb.google.com/eritter or www.ernieanderica.info/ look in lower left for "rocketstoves" and "Rocket Stove Permitting" links.

[shane]

Has any body tried using cast iron for a heat riser? I managed to scoop some discards from a construction site in various lengths in 4",5" and 6" diameters. I was thinking of using this for the whole J tube as well, not just the riser.

[Donkey]

I haven't.. But I see no reason not to.
One thing about building the whole works with pipe. It's all a bit too smooth. Round pipe sections tend to promote laminar flow conditions, too little turbulence for good fuel/air mixing.

Just try it and see what happens, might not be a problem, just something to think on.
I'd try it outside in a test bed of some sort before making a permanent installation of it.