My portable Rocket Mass Heater

[matt walker]

I built a portable RMH in my shop, as a test for eventually building one in my house. I came up with, I think, a good idea for the container. I built it in a metal stock watering tank, 2'x2'x4'. It's a 6 inch system, and works very well.

Some things Iearned:

I found clay pavers for 20 cents each, about the size of a firebrick but not as thick. I stuck one in my woodstove for a week and it came out with no visible damage, so I used 'em for the burn tunnel. So far, after a dozen or so burns, they are holding up great! Much cheaper than firebrick.

I started trying to stack up the pavers to create the exhaust manifold, and then realized I could just shape the whole thing out of clay. This isn't a new idea, but I had no experience with clay or cob so was hesitant to proceed that way. Once I started molding it, I was laughing. It's sooo easy and fun to shape with the clay! I'm just wanted to encourage anyone who is thinking about this to just go ahead and do it. I dug up clay from my property where I thought previously there was none, and just went for it. It's a blast, and solved a lot of problems I was having a hard time with in my head. So yeah, just do it!

I used 5 six inch elbows to make the exhaust spiral up from the bottom of the stock tank to the exit, then back filled with clay and rocks for the mass. It works great, there's a good sitting area on that end of the tank, and the barrel throws off a lot of heat.

So, it's a self contained unit that has a 2'x4' footprint, and a metal housing. I think one could build one of these and set it on something to protect the floor, and run this in just about any location. I'll get some photos up soon.

[Lollykoko]

I'd be interested in seeing a photo or two, Matt. I picked up a couple of used stock tanks last year and one of them will not hold water any longer. Just knowing you've done it already is giving me ideas.

[matt walker]

Okay, I just went down to the shop and took pictures. I remembered why I hadn't documented it already. I didn't burn the paint off the barrel before I built it, because I was excited and in a hurry of course. My rationalization was that I was going to move it into a greenhouse in a month or two anyway, it's just experimental. So, here it is, with it's toxic barrel paint and everything. Lol. Don't try this at home kids. Oh, and I exit the exhaust straight up for this one, again, I didn't want to cut the tank and take it out low until I place it in it's final location. I do envision exiting the exhaust out the side somewhere so that the seat I mentioned would be clear and the flue would heat seedling tray benches or beds. So yeah, this is an early prototype. I'd like to finish that bench area flush with the lip of the tank for the final installation.



Here's a shot with the flash of the feed tube. I like how the tank contains the mess.



And a better shot of the mass. The flue does a full 360 degree circle in there after it exits the barrel and before it exits into the pipe. I'd say maybe 5'--6' of flue in the mass.

[matt walker]

Interesting. This forum software seem to be cropping the photos so they don't blow up the page. I guess that's pretty cool. Right click and "view image" to see the full size, especially the feed tube one.

[pa_friendly_guy]

Nice job Matt. How does it draw through the rocket part? Does it sound like a Rocket when you fire it? I agree with your idea of running the exaust out the side when you have it in its final spot, and maybe extending the cod bench to heat the seed trays. That would serve 2 ways, heating up the bottom of the seed trays as well as providing more mass to hold the heat longer in the greenhouse over night. The Mass of the rocket mass stove is what really provides heat over a long time. It is the fly wheel of the unit. When I saw a rocket stove on U tube I was very impressed and wanted to build one. They have a small one used for cooking that they think will greatly improve the lives of people in the 3rd world. For 1/2 the people in the world the Kitchen is the place to store your dishes, pots and pans and other cooking things. For the other 1/2 of the world the kitchen is the place where they build the fire. They want to build them for $10 so that they are afordible over sees. I built one out of a square metal can that had cooking oil in it from a restaurant. I cut out the top and saved it, then I bought a 4" 90 piece and 1 4" straight piece. Cut a hole in the side to take the 4" pipe and filled the thing with wood ashes for insulation. Then cut a round hole in the top piece and put it back on top. I had an old grate laying around that sort of fit. I cut up an old tin can and placed it in the lower opening to act as a grate for the fire. The total cost from my local Hardware store was $10.05, just a bit over their budget. It works wonderfully, just as advertized.

[matt walker]

Yep, it's very rocket-y. I paid a lot of attention to CSA and it works very well. I'm sure partly because of the relatively short system length and the vertical flue at the end. As you noted, it still needs some tweaking for a final install. This version really doesn't have a whole lot of mass, and I do intend to maximize the mass in the final install. One other thing I'd like to add is a cleanout under the barrel. I'll probably put a 6" T in line with the exhaust right at the exit of the barrel, and have the "leg" exit the stock tank, with a cap, so I could clean the ash from that area.

I'd love to see your rocket cook stove. I've got a rocket oven in my immediate future. I can't wait.

[Lollykoko]

Thanks for the photos, Matt. One of the stock tanks is rusting around the bottom, so I was already looking for some way to re-purpose it. The thought of building a smallish RMH at the campsite has been tugging at me for at least a year. I'm getting tired of cooking over an open flame on the ground!

[dave brenneman]

The oven I liked the looks of the most was this one: from alexia allen's bow drill/ wood fired pizza oven video. It seems like it has the benefits of a fire-once model, with the added option to build up the fire again without removing food from the cooking area. and the hinges that let the door slip into place are a really nice touch.

[matt walker]

Yeah, that's a neat one. I'm pretty sure the part where she started the fire was photoshopped. I can tell by the pixels. Ha, kidding! Seriously, how cool is that!?

I've got a design for mine I'm excited about. I don't know how to draw on a computer, but I might try and get a design up here so you all can check it out. I love the idea of using rocket tech to use a very small amount of fuel to heat the oven.

[eeldip]

seems perfect for heating a cold greenhouse... although it would be nice if you could design a mechanical wood feeder hooked up to a thermostat. then you could use it for a hothouse...