Dabumb wrote:
I have a friend who is a welder and he's wanting to build a rocket stove out of steel just like a cast iron wood stove. Does anyone have any info on this or know anything that has been tried before. Thanks
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Dabumb wrote:
I have a friend who is a welder and he's wanting to build a rocket stove out of steel just like a cast iron wood stove. Does anyone have any info on this or know anything that has been tried before. Thanks
Len wrote:
this guy has done it:
http://www.iwilltry.org/b/build-a-rocket-stove-for-home-heating/
Some things to note.... From everything I have heard here he has done it wrong
1) 4 inch CSA is too small.
2) riser is insulated... but just barely.
3) exhaust is aluminum.
Some of the things he has done right...
1) no mass, this makes up for a lot of the other funkiness.
2) Riser is insulated some... better than none.
3) feed tube depth (top to bottom) is short. It doesn't look it, but remember only 4 in. CSA.
4) He hasn't made it permanent.
5) I think one of the reasons he has no smoke back is that he only burns for a short while...
note his comments that the room gets too hot quite quickly... Mass would even that out.
6) the whole bottom of the burn tunnel slides out for cleaning, Barrel can come apart for cleaning.
Anyway, it works as it is. For a portable unit like this, a good mass might be solder. Find some that melts around 350F.... (the stuff you use for plumbing is a little higher I think normally 50/50, you would use the 60/40 stuff) Put another cylinder outside (or inside) the barrel sealed at the bottom... fill the gap with your mass. It should give off a lot of heat as it transitions through phase change. A light layer of insulation on the outside would keep the stove from heating the room too fast when fired and slow down the cooling of the phase change mass after firing.
Wish I had a few hundred pounds of solder to play with (I may not need that much)
One other comment... his comments about how it works are sparse, which for his purposes is ok. We don't know how clean the burn is really, just that the thing gets hot and doesn't use much fuel to do so.
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Erica Wisner wrote:
Cool project! This isn't a Rocket Mass Heater, though - it's a radiant container around a very small Rocket Cookstove (Aprovecho-style). The barrel never comes in direct contact with the exhaust. That may be an important part of why his 4" system is working.
I think his insulation might be surprisingly good - we used a thin, mineral-felt insulated pipe for demonstrations, and it does maintain a good heat differential, for a good long time. There must be some heat escaping to heat up that radiant surface, though.
Solder is a very interesting idea. Haven't heard that one yet.
Makes me think of the liquid metallic sodium on nuclear piles....
Could be very dangerous if you have mercury or flux in your solder, the vapors could be emitted at unpredictable times. And you'd need the right container, nothing that would let the molten metal escape or pressurize...
But with the right metals for the right temperatures, it could be a very interesting project.
And portable, too, with the solid solder helping to protect the other parts from shifting or warping.
Of course, the RMH originator would probably roll his eyes, and suggest that solder is best used for soldering useful things like cook-pots, circuitry, and water-tanks, and that dirt is a much more economical thing to use for mass.
Len wrote:
I want to try the bench with a relatively large space/passage. In the range of 6inches wide (assuming a 6inch riser) and 12 to 14 inches high... or two 6inch pipes in parallel with joins every once in a while. The exhaust from the barrel goes into the top one and comes out from the bottom at the other end to go up the flue. The idea is to slow the gases and give them some chance to stratify. The masonry heater boys call it a bell. (the barrel is actually a kind of bell)
I also want to try making a bell with just a vertical flue that is blocked. The long term use would be to heat a room one floor up.
Anyway, when/if I get that far I will tell all my findings.
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Erica Wisner wrote:
Look forward to seeing them.
Sounds like you're on track with most of it... the boat explains a lot BTW, Ernie is also a mariner. Seems like sailors have a leg up on the fluid dynamics and general hands-on innovation stuff.
Re: the bell: With the right configuration, this may work just fine. But you may need to reduce the heat-exchange length, and keep the exhaust hotter like the masonry heater guys do.
So be prepared to swap in other features that increase draft, as you swap out the RMH's dimensional constraints.
Len wrote:
A taller riser may help, I was reading in some of the Aprovecho documentation that seemed to indicate if the riser was too high it would actually blow the flame out. Most seem to be 36inch, but I think my "barrel" would be good to 48 or so. If it was constantly blowing itself out.... the cutting torch is my friend.
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Erica Wisner wrote:
Just FYI, the Aprovecho folks and the Rocket Mass Heater folks were not on speaking terms for about 15 years. So they developed different 'rules of thumb' for different types of stove. Be aware these are two separate labs, and they don't necessarily use each other's research.
In our experience, a heat riser where (without the barrel) the flame path reaches up to near the top of the heat riser, tends to work pretty well for RMH's. A little flame poking out, or flame almost to the top, is fine.
I don't think I've seen anyone build a too-tall heat riser on an RMH, if only because the barrel and indoor height tend to set effective limits on what's convenient.
(Putting out the fire may be more likely with the Aprovecho L-shaped cookstoves, where the fuel must be hand-fed inward, and air is often drawn over the top of the fuel instead of through. I know they recommend adding a fuel/air shelf to get more air in underneath and help deal with this.
The J-type downdraft stoves tend to benefit more from extra draft, burning hotter, and self-feeding the wood faster. I haven't seen one 'blow out' aside from the very initial kindling stages.)
compostcanman wrote:
also wondered if anyone knows about the efficiency of a masonry heater compared to a rocket stove. thanks
It's a tiny ad only because the water is so cold.
Rocket Mass Heater Jamboree And Updates
https://permies.com/t/170234/Rocket-Mass-Heater-Jamboree-Updates
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