Rocket mass heater/stove in my nomadic van?!?

 Hello!  I am totally fresh and green to this place!! I loved finding/buying/watching (some) of the 177hrs of permaculture and 8-dvd set of mass heaters videos.  What began this curious knowledge seeking journey was my interest in installing a wood stove into my nomadic cargo van build.  But most people in this nomadic "vanlife" advise against wood stoves because they are to heavy when large and the small ones still create to much smoke as well as don't heat well while needing constant feeding through the night- in the winter its horrible.  For the most part that seems true because I see people try it in their vans and use these very small and inefficient stoves for heating and they use lots of wood to barely heat while creating lots of smoke.

  After delving into all these rocket mass heater videos I think a rocket mass heater is a viable solution for me!!  To think I could solve my heating solution and design a way to cook from it too would be fantastic- though it looks like I already can cook on the manifold barrel!  But I had a few questions if anyone would know of a direction for me to look or have straight up answers that would be great.  

p.s. My living space (contains all the things) is 6ft high, 6ft wide, 12ft long.  So I am pretty sure a RMH/S would be plenty and multipurpose-able.. I think?

1. Chimney hood/cap: If the chimney tube for the RMHS is through the roof I know its pretty much smokeless but would a chimney "cap" mess up the "flow"?  If it did then how could I design the cap to keep the rain/environment out of going down the chimney without messing up that "flow".  

2. Being level:  I know being level is a big deal, but as on occasion while the build itself may be level, if I am parked somewhere that isn't entirely level - will that be a dealbreaker? :(  

3. Weight:  My cargo van has a pretty hefty payload.. But keeping things balanced is important to me because it is my house and I do drive my house around..  Is the RMHS something I can contain in just a metal frame with say - the a ceramic fiber isolation method for the raiser to keep the weight down.  

4. Driving/bumps/vibrations.  My suspension is pretty rad, but I fear for something like the RMH because most builds are brick/mortor/cod and with enough vibrations they will definitely shift and crack apart..  Is there a way I could avoid brick/mortor/cod entirely and use almost entirely ceramic fiber isolation and I guess steel/SS to keep it in place?  I can weld and have a welder available.  So something like a steel/SS box frame to weld all the pieces together and onto the frame.  J firebox tube + raiser + manifold + chimney secured with welding or whatever works.

For any help or link suggestions would be great!!
:)

Check my post at the bottom of the page.

https://permies.com/t/80/71700/Tiny-House-Cook-Stove-Heater#878227

I think this could help.

Hi Josh;  Welcome to Permies! And welcome to the wonderful world of rocket science!

First, Max has given you a link to a post here at Permies . Matt Walkers tiny house cook stove / heater.  That is one awesome build and could work very well for you.
Another is this build, Kirk Mobert's casarole door brick bell , although it would need a flat top cook surface built in. here is that link.(permies.com/t/71576/tiny-house-rocket-mass-heater)

Now on to your questions; #1) All rmh's use a chimney cap. I use a simple "coolie" cap on both of mine and have never had any issues. Attatch with screws and your good to go.
#2) Being not level will not affect performance at all. #3) The mass (if you use one) can be contained with almost anything.  Brick is common as it holds heat as well (added mass) but sheet metal, sheet rock, wood boards , plywood, they all work. Only the core burner need be brick, and non flamable material.  Using ceramic fiber boards in your core rather than heavy firebrick will save weight, using Morgan superwool to build your riser will save more.  Be sure to get a barrel with a removable lid as you will need to check your riser each time you have moved your van very far. The riser could tip if the road is rough and you really don't want to try starting one if the riser is not properly placed.

#4) Your core could have an angle iron frame you bolted thru the floor to help keep it in one piece.  


Congradulation's on your first steps towards being a rocket scientist!  Soon there will be no going back .... you will find yourself telling complete strangers all about rmh's ... you will be spotting "free" wood
that you will have to stop and pick up! You will start noticing regular wood stoves belching out big clouds of smoke and be thinking that they need a smoke free rmh....You could go regale them with RMH info...

Enjoy the journey!

The difficulty with a nomadic rocket mass heater is the middle word: mass. In order to do its job, it needs to be heavy, many hundreds of pounds, but the heavier it is, the more problems you will have driving it around. This is one place I think a water mass would be the best solution. Designed right, you could work it to have the combustion core heat a water tank for storage, yet drain the tank for moving around, and refill it at the new destination. Water will have significantly more heat storage capacity within a 212F/100C temperature limit, so space can be minimized, and mass will be significantly less even if not drained for moving.

A related issue would be moving a masonry mass of any kind. Brick or cob would be subject to cracking from vibration and road shocks, and would need to be stringently contained in order not to fail. The combustion core would probably have to be ceramic fiber to avoid damage from moving.

My concept would be a double barrel, say a 30 gallon drum inverted inside a 55 gallon drum so as to make a hollow shell of water open at the bottom, with a 4" batch box core under and inside the 30 gallon drum. The exhaust from the internal space would be collected and sent out the chimney.
This would not be a cooking device, unless it could be arranged so that the top of the firebox was exposed and accessible for cooking. If the outer drum was arranged so the water level was just below the top of the inner drum, then there would be a hot surface that could be used for cooking, at the expense of somewhat lesser heat storage ability.

Joshua Hozjan wrote:p.s. My living space (contains all the things) is 6ft high, 6ft wide, 12ft long.  So I am pretty sure a RMH/S would be plenty and multipurpose-able.. I think?

I'd been looking at this possibility as well. I wouldn't move the van much though from it's winter residence, and use different transport. I guess I'm not into the stealth aspect so much.

Joshua Hozjan wrote:3. [...] Is the RMHS something I can contain in just a metal frame with say - the a ceramic fiber isolation method for the raiser to keep the weight down.  

As others wrote the ceramic blanket riser would work well. Tim Robertson used a thin cloth dipped in refractory or furnace cement instead of metal to hold the riser shape.

Joshua Hozjan wrote:4. Driving/bumps/vibrations.  My suspension is pretty rad, but I fear for something like the RMH because most builds are brick/mortor/cod and with enough vibrations they will definitely shift and crack apart..  Is there a way I could avoid brick/mortor/cod entirely and use almost entirely ceramic fiber isolation and I guess steel/SS to keep it in place?  I can weld and have a welder available.  So something like a steel/SS box frame to weld all the pieces together and onto the frame.  J firebox tube + raiser + manifold + chimney secured with welding or whatever works.

One the firebox yes this is my concern too, especially if driving on a rough dirt road, that the bricks may crack if they're allowed to bounce at all. I also guess a steel/aluminum frame would help (video).

For insulating below the firebox I'm not sure. I guess with enough distance any wood won't char, if you decide to use wood floor beneath or near.

For the bench I was planning on a wood box filled with gravel, page 58 of the RMH builder's guide has a bit of spacing between the firebox and the wood box I plan to do, so they can be more easily disconnected and removed during summer.

I'm also thinking of trying a horizontal chimney (page 205), but with the outlet pointing down drilled through the van floor, behind the rear axle. Behind the rear axle so that a skirt can be put around everywhere else, and air flow beneath vehicle will pull. Problem is if it gets snowed in I suppose.

Hi Andrew;   Nice van your converting.  
The gravel filled bench has been used successfully but it is not the best of choice's.   Have you considered a half barrel system? They work very well and weight might be less than a gravel bench.

Any wood under a core unit is in danger of pyrolysis. The safest way to have a wood floor under a rmh is to raise the whole core unit up with flat bricks and cement board, then clay / perlite on that.

Your idea of the under floor vent sounds like it might be problomatical. Could work great , might work most of the time ... or might be a big pita to get drawing....  
You can certainly give it a go and let us know how awsome it works OR... why its not a good idea.

I keep thinking of when I disassembled a chimney and moved the clay fire bricks around in a metal wheelbarrow, stacked 2-3 high mostly organized/level. Maybe 5-6 of the bricks had fractured in transit over 8 or so loads. I guess clay slip between the bricks and having the bricks laying a bed of vermiculite instead of metal would help a lot. So maybe a metal frame not necessary... I guess experiments needed to see failure points (like this video claiming weight of stuff on bricks caused some bricks to break).

thomas rubino wrote:The gravel filled bench has been used successfully but it is not the best of choice's.

Page 214-218 I agree that the box and fill system seems best to allow nomadic folks to more easily transport the heater. New fill being added at each location to avoid the cost of transporting the heavy mass.

Can be filled on site with a sifter and shovel (a few hours and you'll have a lot of gravel... frozen ground may make things really tough without pickaxe):


And I agree, gravel seems worse absorbing the heat (page 86). I wonder if you could make a hybrid gravel/water bench, use liner like you'd see in a aquaponic/hydroponic bed, which they also coincidentally fill with gravel:


Water seems to have the best heat storage... best to have backup system to mitigate freeze problem though or some passive drain inspired by bell siphon as hydroponics folks use but driven by a phase-transition spring valve.

pH adjustment to minimize aluminum corrosion (7.0-8.5 seems fine). Seal the ducts with silicone, have them enter/exit above the bed to not deal with perforating the box sides.

I am concerned both at cost and the longevity of liners in years especially at higher temperature (near 100C), so I am interested in investigating this Pond Coat: Seamless Brush Grade product. Seems promising though I hesitate after seeing in forums skepticism of similar black rubber products not lasting more than a few years in their outdoor ponds (could be sunlight deterioration in those cases, not sure).

thomas rubino wrote:Have you considered a half barrel system? They work very well and weight might be less than a gravel bench.

I didn't see anything to convince me that a half barrel bench (stratification chamber) would be optimal. I see how that is intuitive though, a stratification chamber bench may help with sending the coldest exhaust out the floor through internal turbulence/convection somehow perhaps having more heat transferred to the mass than ducts (more metal surface/mass would release heat into the pebbles over time? like a copper bottomed pot?). But the problem remains that there is less bench mass/volume, and space is at a premium in van/rv (trading space to have more efficient heat transfer to pebbles, but you have less pebbles/mass). Plus I'd have to cut barrels in half and haul them around instead of just dumping gravel. But could be optimal for someone who chose to routinely drive around with this mass during winter instead of mostly staying put adjacent to their gathered firewood as I'd expect.

thomas rubino wrote:Any wood under a core unit is in danger of pyrolysis. The safest way to have a wood floor under a rmh is to raise the whole core unit up with flat bricks and cement board, then clay / perlite on that.

I see some more details page 216 of RMH book. Duraboard looks promising.

thomas rubino wrote:Your idea of the under floor vent sounds like it might be problomatical. Could work great , might work most of the time ... or might be a big pita to get drawing....  

Reading this thread on cooling the feed tube makes me think it will work out. I quote:

Konstantin Kirsch wrote:A RMH has minimum 2 pumps: First the heat riser pumpes the hot air up. Second the barrel pumpes the air down on heat exchange over the surface.

If you do have a vertical chimney than you have a third pump.

At my RMH I got the problem that the feed tube got very hot in time. After some hours of use the temperature rises up to 900 °F. A new wooden stick starts to burn on all sides and on the total length immediately after putting it into the feed tube. Than smoke comes into the room...

Now I added a fourth pump at my RMH: On cooling the feed tube the wood is only burning sideways at the bottom. There is no draft upways in the feed tube any more. There is no more smoke coming into the room. There is no probem anymore on closing the door quickly and there we got hot water!

I took the feed tube out of steel and added a thick plate out of steel to it

Than I put a put with cold water on top. he feed tube getts now cooled by the water and the water gets hotter.

I see no problem in my design as long as the heat riser is primed, firebox is cooled, and bench not too long/resistive. As there is no vertical chimney there will be no third pump to fall back on as redundancy, it would be critical to have the first two and fourth pumps optimally designed and within operating conditions (riser primed, firebox cool).

Filling the pebble bed would be done with snow melt in this pot, melted in the process of cooling the feed tube to maximize the draft of first j-tube thermosiphon. Note he says his pot of water isn't enough mass and he said he wanted to look into an active heat pump to keep it cool; I think an overhead water tank best solution as a passive thermosiphon, easy hot shower for example, recharged by snow/rain? I quote:

Konstantin Kirsch wrote: but the waterpot has not enough water in it. I produce much more boiling water than needed. In the time the feed tube gets too hot even I cool it with this system. So I found that the cooling of the feed tube is very importand. I'm realy thinking of making an aktive water cooling system direct around the feed tube.

As Paul Wheaton says in this podcast if there isn't much mass in the riser (just ceramic wool instead of brick), it might not retain enough warmth from the last firing and may need to be primed anyway.

Page 247 'Thermosiphons and Chimneys':

A J-shaped thermosiphon (such as our firebox) operates in a similar way as the reverse-J water siphon. The short leg is near the source of fuel and air. The flames follow the longer leg upward, creating a strong draft. [...] In addition to a difference in height and the absence of leaks, a thermosiphon also requires a consistent temperature or difference in temperatures. If the short leg became much hotter than the long one, the thermosiphon could stop working or even flow backwards.

Page 248 has some chimney draft math as well.

Advantage of this system, not having that third thermosiphon (vertical chimney) is not having that heat loss from the mass through the day that Paul Wheaton talks about often where he advocates the horizontal outlet instead of vertical chimney (not sure what present status of that debate is...).

In the podcast it seems of the 3 shippable core designs: Erica's design using "goo" is a clear winner for portability, low weight, and low cost, and Paul Wheaton says they may release that design in the future. Ok, I see it didn't last and had crumbled and they settled on Paul's wood box design.