Mini Rocket stove/mass space heater.

Well I've looked around for a few weeks now about these and have not found anything small enough to be placed in a fireplace and light enough to be moved around to various rooms. The idea is sound, I used regular soup cans for the burn tunnel and riser, insulated with baked bean cans and clay/perlite and it burned nice and hot. The reburn drum is going to be made of 2 #10 cans and I will use soup cans again for the exhaust. This will all be sunk into a boat shaped metal container and covered with clay from a local creek bed and allowed to slowly dry in a plastic bag for the next month. I have tested it, and the plan is for the exhaust to go right up and out the flue. I will post pics as I go along, which should be today....

I started with regular old condensed soup cans for the horizontal burn chamber, riser and exhaust pipe. But I opted for the slightly larger vegetable can to get an ember pit in the feed tube. Edit: Almost forgot, I used a #10 can lid under the vegetable can, since its so much thicker.

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The horizontal section runs slightly up hill towards the riser, but only slightly.

This is it with the horizontal burn chamber encased in concrete.


The idea is to run it for an hour or two using a fan to circulate the heat off of it.

I know concrete isn't the best material, but i used it because the cans could eventually burn away and the concrete would hold the shape. The top of the boat will be encased in several inches of clay/sand mix and allowed to slowly dry in a plastic bag for a month or so before putting fire in it, so if its going to crack it will be in the drying process.

Insulation for the riser. The outer cans are tomato juice cans, a whole one and one cut to about 4 1/2 inches:

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I built a platform around the first riser can by rolling a slab and using a can to notch out one side, then placed the riser on top and leveled it.

Then I sculpted the exhaust chamber, I had to use a river stone to keep the #10 can level at first. I also put a depression in the concrete to give some extra room for ashes.

Looking down the riser and reburn barrel.

I cut the bottom can to about 5 inches to keep total height at around 1/2 inch to an inch higher than the riser. I used a soup can with the bottom cut off and an arch taken out of it to start the exhaust.

Then I encased the bottom can and up to the first ridges on the top can, about 2 inches, in 1/2 inch thick clay for tonight.

Tomorrow I will add another 1/2 inch and smooth it. The nice thing about clay is that you can sand it when it is dry but hasn't been fired. It will be smooth as a baby's butt.

I wrapped it with a garbage bag for the night. The bag extends dry time, hopefully preventing cracking. I might have to periodically spray it to keep it from drying too fast.

Pretty much finished now, gonna wait to put the exhaust on until it has dried and I can test it.

Now to let it dry for sanding. I used a really sandy mix for the outer 1/2 inch so hopefully it will help with cracking.

Eventually I want to build one of these in a wheelbarrow. The advantages would be three fold:
1. More mass, for longer heating.
2. Portability, just need to have more than one exhaust port that leads outside. Then you just cap both ends of the stove and move it to another room or building, park it under that buildings stove pipe. Bam portable heat source.
3. It is removable. So if it gets too hot for comfort inside, you can move the stove to the porch and let the inside cool down some before bringing it back in.

And a 4th: If you have a refrigerator solar food dehydrator and it isn't quite drying the food, you could hook this up to it temporarily to help it finish.

Here is a scale illustration.

I like the portability idea.

how would you take things apart for cleaning/repair/inspection?

What are you going to use for an exhaust?

Do you have something to route the heat out?

I'm a little worried that there might be some bottlenecks which would cause smokeback.

dave brenneman wrote:
I like the portability idea.

how would you take things apart for cleaning/repair/inspection?

What are you going to use for an exhaust?

This is the kicker. I plan to use a vacuum to clean ashes out. Of course let it completely cool then vac the front and wrap a rag around the vac hose do the same in the exhaust. Plus the exhaust will be pretty short so I can make a tool out of a hangar and a can lid to scoop ash out. As for inspection, I guess I would have to take it apart.
Well the exhaust is going to be made of more soup cans.

paul wheaton wrote:
Do you have something to route the heat out?

I'm a little worried that there might be some bottlenecks which would cause smokeback.

Its pretty roomy around the base of the reburn barrel. An open space and 1x1x3 inch space wrapping to the exhaust on each side.

This is beautiful - a work of art! It's been three years since you posted. How is it working? What size area is it used to heat? How has the cement held up? How often do you have to burn? How long does it radiate heat? Lots of questions, but this inquiring mind wants to know. Thanks! ~Jacq

It appears the OP is no longer registered on the forum, so I don't think you will get a reply.

There are so many things wrong with the details of this build that I hope nobody tries to copy it as-is. A rocket heater like this *might* be workable if built with all correct materials, starting with insulating refractory cement instead of concrete. The concrete shown would suck heat out of the tiny burn tunnel and never let it get to an effective combustion temperature... and if it did eventually get hot enough to be effective, the concrete would deteriorate from the heat as the cans burnt out. The riser appears to be vermiculite, possibly mixed with some clay or something, hard to tell from the pics, poured between two cans. If not structural by itself, the vermiculite will fall out as soon as the inner cans burn out.
It would be interesting to see the results of a well-done experiment like this.

Oh, and the clay wrapped around the outer "barrel" is guaranteed to crack and split off as it dries, no matter how slowly it is done. Clay shrinks when it dries, and clay over smooth rigid metal cannot hold together. A wrapper around the clay would be needed, or reinforcement embedded in it.

Agreed. That's why I was so curious. When I finish my permanent rmh, I plan to experiment with a portable version, but not one as small as this.

I have a small cabin (14x20) which we go to 90% of the time during nice weather, but hoping to do more in the colder months. I would LOVE / Planning on building something like this which is portable so I can take it out during the summer for the space. We really don't need much warmth (this is initially to huddle around in the mornings... It's really find once the sun comes out most of the time). Anyway, I'm looking for something I can move without a HUGE amount of work.

Would insulated refractory cement do for the riser? I was planning on using cardboard tubes and let it just burn off after it's set. If the inner cans are going to burn out, I would like it just to happen... Unless I can find some cheap think walled pipes to use.

I've searched around and haven't found any nice plans for a small / portable RMH. I've seen a few pictures, but nothing with this level of details.

I was also thinking of using a small stainless steel trashcan as the base (since I can find them locally). But my wife likes this look of this one better and she might win. So wondering what I would have to modify to get this going nicely. It really does have a nice look to it.

Thanks

For the summer use you describe you really don't want the mass heat storage aspect, but more an efficient quick heater. Would you be connecting the heater core to an exhaust duct/chimney, or using it in an open area with free ventilation?

Drake Woodring : Welcome to Permies.com, our sister site, Richsoil.com, and a Big Welcome to the Rocket and Wood stoves Forum/Threads


To help you visualize what I am going to talk about go look at the size of the Exhaust pipe/vent on your primary heating unit !

Unless you live in a castle your exhaust pipe's diameter is going to be 8'' or less. It would seem to make sense that we could
just make everything smaller, or downsize our heating unit to end up with what we want ! Short version, this is not going to
happen !

If we take the 8'' diameter pipe we can find its Perimeter 25.12'' and the Cross-sectional Area C.S.A. is 50''~ish sq. in.

If we take the 6'' diameter pipe we --- find it's Perimeter 18.84'' and the Cross-Sectional Area C.S.A. is 27''~ish sq. in.

If we take the 4''………………………………………………………………... 12.56'' ………………………………C.S.A. is 12.56''~ish sq. in (Equalizing)

This keeps happening- as the inside surface area of the pipe shrinks slower than the C.S.A. We have a higher percentage of
surface area to volume. Here, more and more the gas flowing through the pipe is slowed down due to the effects of friction
and the characteristics of laminar flow !

The 1st thing we lose is the ability to flow our hot exhaust any real horizontal length to create a Thermal Mass bench, in
effect we have a Rocket Mass-less heater !

The people at Dragon Heaters dragonheaters.com have several commercial kit models for the D.I.Y.Builder/owner with
well functioning 4'' units, their castle model is close to what you need ( this is a guess you did not give us a location !)

The original build for this unit never had any real chance to work, but it has been a source of meaning full conversation on
that point and adds to our general knowledge base. For the good of the Crafts! Big AL

Late Note : While only something that could be used outdoors on a Sheltered Patio, and not highly portable you can do a
Google search for ''Tea Stump Rocket Stove''- if you get re-directed to stump tea thats bad, however Tea Stomp rocket stove
is good !

Lite weight, durability, insulation, and strength are only possible as a series of compromises. Good luck/Good hunting Big AL