Hello Judith,
thanks for the enthusiasm. That's a nice slug of questions there!
Judith Knapp wrote:Hello to all the experts!
I am a learning Rocket girl with a serious interest in installing on in our house. We have a shared wall that is going to come out and I want to know if/how we could install a rocket mass WALL of sorts. Does the structure NEED to be horizontal, or could we route it vertically?
You can certainly do a vertical wall. I'd still route the exhaust like trail switchbacks with a gradual upward slope, not zig-zagging up and down, for best results.
Does it need to be away from other wall structures?
Are we talking combustible walls, up to code, or "what can I get away with"? Code is 5" masonry thickness, 4" air gap to other walls, and if you need to make a structural or air-seal connection you can do it with a "wing wall" not wider than 4", extending outside the main part of the heater. If it's near a corner it must be at least 4" long, if near the middle at least 8", to allow adequate heat dissipation before contact with combustible walls. Now these specs were designed for masonry
heaters with surface temps around 150 to 250 F;
rocket mass heaters' heat-exchange areas usually run more like 80-95 F, so you will be more than safe using this method.
Can we safely cover the barrel in brick or cob without compromising it?
We have found that covering more than 1/3 of the barrel in masonry compromises the downdraft effect. But the upward structure of your heater may compensate by boosting the exit draft.
I would not recommend burying the barrel in a wall or permanent structure, as this makes it very difficult to get at for maintenance or to troubleshoot unexpected behaviors like clogging.
Is there material besides a barrel that could be used for the burn circulation centre?
David Lyle's
Book of Masonry Stoves gives some ideas, and I have seen some work with tile chimney liners. I have not yet seen a method I would endorse without reservation; they don't shed heat fast
enough to preserve the downdraft effect that the metal bells do so well, and the single-wall methods seem vulnerable to cracking. Ceramic parts for this job are also pretty expensive. I have a PDF on ways to replace or decoratively cover the barrel that are compatible with the design as we know it today, if you're interested.
If what you really want is a tower-style contraflow masonry heater, you might also want to take a look at the historic, proven designs like Swedish, Finnish, and Russian contraflow heaters. These will be more expensive than your average rocket bench, but they are much better time-tested, and some come with extra features like built-in ovens or flame-viewing windows that are still a work in progress for rocket mass heaters. Might give you some design ideas, and a sense of how far the boundaries can be pushed, regardless of your final choices.
These are incredibly brilliant and I have been inspired by Ernie and Erica's innovations in this area (and the other permaculture sections, but we're not there yet).
Any advice would be huge, thanks!
Flattery will get you anywhere. Hope this helps.
-Erica
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