Andre Wiederkehr

Now with diagrams.
As before, let me know if you have feedback from trying it out.

Tony, thanks for more info about that article. With the date I was able to dig it up in the Internet Archive. Looks interesting. Not sure whether it's what I want, but definitely will keep it in mind.
The Energy Saving Stove

Coydon, you're in a pretty cold location for yurt living! Although I have run into a few in Ontario at Ottawa latitude and in central Vermont, both of which also get pretty cold winters.
Your reflections on the materials are worth hearing. Thanks for sharing them.

Coydon Wallham wrote: One element of "local" is how to view the existing production and distribution networks. 'Scrapping' makes use of readily available materials that would otherwise become landfill waste. But if use of such materials becomes part of a codified, growing system, it helps reinforce production methods that produce waste and excess. It would seem a tough call at what point making use of 'waste' products becomes encouragement to produce more of that waste. Using scrapped materials though often makes an RMH more reliable and reproducible than creating a similar element from local, scratch material. I guess that is the trade off you are looking to find help deciding on?

My own journey is a mixed focus on here-and-now impacts and modelling visionary alternatives. I sometimes follow the salvage mentality in areas where I am choosing to not give up a technology (e.g. some internet access: I got a computer from community computer recycling NGO), or where doing so has a positive footprint impact (e.g. a more efficient biomass cookstove from scrap metal makes less air pollution than a three stone fire - maybe important given how many people we have right now). I think the modelling of true alternatives is important too. As you say, depending on salvage ultimately requires the continuation of the present system. So I don't want to eat primarily on dumpster diving, or mulch my garden with cardboard, or get all my clothes at thrift stores, even though those things are possibilities in the wasteful context I'm in. We need people dancing to different music, expanding our collective vision for what is possible and how.

For this particular need, I'm not looking for help deciding which path to lean toward so much as putting the question out there about what options people are aware of so I can make a more informed decision about what to try. What I take from your writing is that you would suggest that I build a proven design so I know what good operation looks like, and then experiment from that baseline later.

Coydon Wallham wrote:As such, I've discovered it would likely have been better to install a 6" system.

Can you explain why 6" would be better than 8" for that situation?

Your notes on cooking are helpful. Sounds like it'd be okay, but not any too much cooking power. I'm a bit spoiled having recently switched my summer cooking from a bare firebrick J-tube to a TLUD based on Paul Anderson's Champion design. It boils water fast, and fries quite well.

Coydon Wallham wrote: I have to wonder what objections you have to wool insulation? Are you referring to rock wool/super wool? Or actual sheep's wool?

Yup, I was vague. I meant ceramic wool - high embodied energy and high-tech/centralized processing needed (very hard to localize). I have no problem with sheep's wool in reasonable quantities. I guess the latter is pretty fire resistant for an organic material - are you suggesting it could have a place in RMH building?

Thanks, Tony. I'm having trouble finding the article you referred to on the MHA site. Can you link it for me?

I want to heat and cook in a cabin. I am curious about building a rocket mass heater to meet this need. I have a lot of questions to see whether it's a good idea, and, if so, exactly how to do it.
I know there's a huge amount of info in this forum already, so if you are aware of specific posts that answer my questions, please do point me to them. I'm just having trouble pulling all the infomation I need together into one place.

Situation:

1360-1540 ft³ room volume, depending on how thick the slip-straw walls are. That range represents 12" thick (leaving a smaller volume inside) to 8" thick (larger volume). I'd welcome input on how thick (i.e. how much insulation value) makes sense given how small the footprint is.

Here's data for my climate (how it used to be, anyhow):

	Oct	Nov	Dec	Jan	Feb	Mar	Apr
Daily Average (°C)	8.5	2	-3.6	-7.1	-6.9	-2	5
Daily Maximum (°C)	13	5.5	-0.5	-3.3	-2.6	2.5	10.2
Daily Minimum (°C)	4.1	-1.5	-6.7	-10.9	-11.1	-6.5	-0.2
Extreme Minimum (°C)	-6.2	-19.5	-27.4	-31.1	-31.5	-32.5	-15.4

I am okay with a cool room in the winter, 14-16°C, as long as there's a warm spot to sit. That's one of the things that attracts me about the mass bench idea - keep me warm rather than the whole room. However, I want the capacity to warm it up to 20°C or so if I have company who likes it warm.

I am working on the land, so I can tend the fire somewhat, but don't want to babysit it all day. I am fine with it getting pretty cold overnight as long as the room doesn't freeze.

The floor is going to be softwood, the walls light straw clay, and the roof steel for now, hopefully switching to thatch within a few years. Support to ground for the mass would be challenging.
I can and will run calculations on the dead load capacity of my floor once I have a clearer idea of the shape of the mass (which affects where the weight lands relative to the floor supports).

Questions
Cross-section of system:
I understand that one can build a variety of cross-sectional area systems, with 6" diameter being the smallest that usually works. I imagine for such a small space it would make sense to keep it as small diameter as possible: 6". Does that make sense? I've heard rumours that you actually need to run quite long fires with some rocket mass heaters to be warm enough, which isn't all that appealing given the repeated feeding required. Would 6" be large enough to allow relatively short/few fires per day?

Stovepipe:
I got some insulated stovepipe for only $25, but it's 7" ID. Is it possible to increase from 6" to 7" at the transition to insulated stovepipe? I think this is considered a very bad idea with conventional woodstoves because the gas expansion results in cooling that may consense water vapour, leading to creosote adhesion, leading to a chimney fire. But I think the exhaust from a rocket stove is already below condensation temperature at this point in the system, so does it matter?

Mass sizing:
I imagine a 6' long bench would be nice so I can sit or lie on it, but I'd rather not make it bigger so it doesn't take up more of the room. I would like to do a stratification chamber design; would a 6' bench be enough internal surface area to absorb enough heat to be efficient? How thick would the walls need to be? This correlates to: how much does it need to weigh to provide enough thermal mass? I need to make sure the floor can take it. It would be nice if the mass is big enough to let me be away for a day or two without the room freezing - is that realistic?

Fire safety:
How can I install the rocket stove and mass so they don't set the floor on fire? My impression is the light straw clay wall should be fine being near or against the mass - is this correct? What about a structural post in the wall buried a few inches into the LSC?

Cooking:
How well does it really work to cook on the barrel? Anyone here using it as their only cookstove in the winter? Are there options that work better than a barrel? Is it possible/practical to build in an oven where the exhaust first enters the bench?

Materials:
I have a powerful ethic of living my life using low-embodied energy, low-tech, local materials. The things I don't love in some rocket mass heaters are: purchased firebrick, wool insulation, foil tape, the barrel, stovepipe, metal heat shielding, perlite/clay mixtures, hardware cloth or hog panel for forming the cob bench... that sort of thing. Perhaps you get the picture. I will use this stuff if I'm convinced it's the best overall option available (compared to much worse performance, or a different kind of stove), but I'd like to push the envelope: how localized can this technology get? How much of it can be made of cob? What options are there for effective homemade insulating firebrick? Are there other chimney options?

Stir fry snow peas (giant snow peas, if you have them!) and add the ricotta near the end with herbs like thyme. Serve with potatoes or polenta.

another one:

Mix with cooked greens such as lambsquarters, add sauteed onions and garlic, cayenne and bergmot or oregano, and use for filling calzones (dough pockets). Can bake in the oven or stove top on a griddle/frying pan, flipping halfway.

I have made and used a wooden version of Burra's corn sheller. It takes a scant hour to make, and works really well. My family has shelled thousands of cobs this way over the past few years. The + shape tapers from one end to the other. Leaving a short non-tapered section on the small end lets me sharpen the corners again whenever they get really dull. When it's too worn down to sharpen it again, just chuck it in the wood stove and carve a new one.

I wrote an article that describes the process here.

Phil Stevens wrote: I replaced the top with a piece of heavy steel plate so I'd have a better cooking surface and because that part of the drum was spalling after a few years of use.

How did you do that? Weld it in? How thick is the plate? I haven't built a RMH (yet!), but as I consider it I've wondered about whether the top would wear through from the intense heat, and also how to make it an effective cookstove, so this is of great interest to me.

Nancy Reading wrote:
You can see from the undergrowth behind that the grass is normally still green, if not growing overwinter, yet the angelica canopy succeeded in shading it out.

That's pretty cool! I will tuck the idea away to try.

Jay Angler wrote:I would look up the standards for land management for organic gardeners.  An old gardening book I have talks about adding 2 inches of quality compost to every bed each year to maintain fertility. I have *no* idea how that fellow managed to get that much compost without importing from outside the garden.

This is a very important topic to me, and the source of my "local nutrients" value.
I've read the same recommendation recently in Charles Dowding's book Compost . I don't have it by me, but I think the recommendation was to start a garden with a 6-8" layer of compost (imagine the wealth!) and then 2" every subsequent year. I think if you do this, you must end up importing from outside the garden.

John Seymour, from The New Self-Sufficient Gardener wrote:
...no-diggers do use an awful lot of compost. In fact, they put so much on their soil that it is almost pure compost. All the no-diggers I know bring in organic material, in large quantities, from outside their property, because no matter what crops they grow, they cannot obtain enough organic material from their own lands to make the necessary compost....
I am not decrying these practices; I think they are marvelous. All gardeners should be constantly on the lookout for organic material and seize it whenever they can. But obviously not every gardener in the world can do it; and you can be sure that if one plot of land is using this technique, it is robbing another plot of land that is either being doused with chemicals or left unproductive.

I have actually seen a few cases of no-till gardeners not importing  from off "their own lands," but as far as I could see, they were probably still depleting the source land, so his point stands. I'm not interested in human concepts of property ownership nearly as much as ecological health.

Importation from outside the garden is okay with me as long as it comes into a fairly healthy equilibrium eventually - basically, that the land it's coming from is not becoming continuously less fertile over time. My fairly basic understanding is this can happen in two ways: either you rotate where you're gardening around the whole area you work with (e.g. compost materials come from 1/2 of the plot of land and are applied to the other 1/2, and every few years you move where that 1/2 over to the other side) or you are taking them from an ecosystem that contains enough critters that are good at 1) producing enough bonus organic matter that you can take some and still leave more than they started the season with and 2) breaking mineral constituents of soil down into nutrient forms available to plants at least as fast as you're taking away minerals.
The former is only practical transport-wise if the areas are pretty near each other. I'm wary of the latter option, because it seems a lot of people assume the source ecosystem can cope with what you're taking away without really knowing that it can. And it might take a while to see if you're doing damage. This is why I'm pretty committed to not importing material from land others are managing to feed the soil I'm working with. And that's where these systems usually run into trouble, because it seems like it's just pretty hard for most people to gather that much material without importing.

Jay Angler wrote:I recall Joel Salatin had a chart in one of his books that mentioned how much of each vital nutrient leaves the farm every time you sell produce or meat off the farm. This leads me to remind you to check out the forum about humanure and responsible use of urine!  I'm pretty sure part of the issue is that some nutrients are harder for plants to access than others. Once you prepare land, the more minimal the tillage, the more mushrooms you can encourage, the more plants will have access to mycorrhizae and microbes to play that important role.

Yup, I love using humanure/urine compost on gardens for this very reason! Cycle the nutrients back to where we received them from (or uphill/upstream/upwind from there...), like many other animals do (perhaps in a less calculating way). I've used Joe Jenkins' methods for doing this in the past, although I'd like to keep exploring if that exact system makes the most sense for me.

I've actually done a calculation of this potential for nutrient loss for the example of maize (using standard nutritional data, which again might not represent the nutrient content of one's particular variety).
So, for example, in the past Arkhipov Dent has yielded 26.3 cups in a bed (which, including the paths, is ~122sqft). This comes to 63 bushels/acre (not that I've ever grown anything near an acre of corn). That's a very poor yield by conventional monoculture standards, but I'm okay with that. I choose to not use all the tricks they do to bump up yield.
The nutrients in this hypothetical harvest would be:

nutrient	lb/ton dry matter maize	lb/acre
C	795	1220
N	24	36.8
P(P2O5)	12	18.4
K(K2O)	8	12.3
Ca	2	3.1
Mg	2	3.1
S	2	3.1

So, if I were to grow an acre of this corn and send it away from the land, the soil would be losing 1200lbs of carbon, 37lbs of nitrogen and 40lbs of mineral nutrients. This is why I don't want to sell food!

If others are entertained by such calculations, I put the table in my spreadsheet at the bottom of the "crop chart" page, so you can sub in your own yield data or that of a conventional field of corn (might be 100-200 bu/ac).

Jay Angler wrote:I would be careful in the short term (until you get more nuts planted) that you do have enough and the right kind of fats planned for harvest. There are "essential" fats, just like essential vitamins. Some of the research I did a long time ago, suggested the fat side of the equation was a much bigger issuer than the protein side.

I've tried to read about this in the past and gotten kind of bogged down in debates about not only getting enough of essential fatty acids, but also the right ratio between omega-3 and omega-6. I think I might be okay, between soybeans, poppy seeds, squash seeds (I eat them from any species, with more less processing depending on the thickness of hull) and black walnuts. As a byproduct of fibre-flax growing, I find I get relatively little seed beyond what I need to replant the next time. I'm reluctant to try to maintain both a fibre flax and a seed flax variety. But maybe I should try to grow more flax seed, as it is higher in omega-3 and would pull the ratio that way a bit along with the walnuts.
Anyone know some pretty straightforward sources on how to get this essential fatty acid amount and balance about right? Maybe I need to add another section to my spreadsheet....