Ok, I'm writing this as a 65 year old, handicapped woman with very little energy and lots of pain. If I can do it, pretty nearly anyone can.
I was first introduced to the idea of rocket mass heaters from Clif High of the webbot project, and just sort of mildly clicked on a link to find out what he was talking about. I got the ramifications pretty fast. I'm 65, my husband is 70, we live off the grid in the Colorado mountain wilderness and have no intention of ever leaving to warmer climes. But using 5 cords of firewood a winter to heat our little cabin is getting to be a really serious burden of cutting, hauling, splitting, ad nauseum. So, a stove that would take a fraction of that amount seemed like a really good idea.
First problem - lack of space for mass heat storage. Ok, after fighting that one for awhile, I accepted it and turned toward a bell concept.
Second problem - lack of space for another 55 gal. drum for a bell and lack of money for other alternatives.
Ok, maybe those weren't the first two problems. One really big problem was my husband who didn't believe the whole principle was real, so he refused to have anything to do with it. I could never have managed it without my brother doing the cuts on the two barrels to go around the inner core. But I did the rest by myself. My husband has since eaten his words. (BIG grin.)
I'm writing this as a person who had not a clue as to the engineering concepts, what makes a draft, how to mortar something - nada. First I decided I could not do anything with cob. I just can't stomp on clay and grass to turn it into mortar. So, I found out about "heat stop" which is a high heat mortar and used that as my mortar mix. I would like to find out about fire clay for the next step - I have built the stove part but have not yet tackled the bell. I just decided that I had to put the stove together and plan to figure out materials that I could afford and could build next spring. Even without the bell, this stove is astonishing in its efficiency. The ashes are practically nonexistent and the temperature on the stove pipe doesn't get higher than 150 degrees.
I learned that there are three basic critical measurements: burn tunnel, heat riser square inch ratio to external pipe ratio, and distance from the top of the heat riser to the top of the barrel.
The heater core consists of a firebox, a burn tunnel, and a heat riser. The opening in the burn tunnel has to be the smallest opening. The square inches of the opening of the heat riser has to be either the same size or slightly smaller than the stove pipe leaving the stove. I bought a ceramic furnace flue for the heat riser because it was so much cheaper than fire bricks. That was a mistake because it made the opening big enough that the stove pipe had to be 8 inches instead of the standard 6 inches. That was ok for me, because the stove pipe going out the roof (already there) was 8 inches. We really don't live with alot of money, so when we built the cabin in the first place, our chimney from the roof up is actually three single wall stove pipes, 8, 10, and 12 inches, to give us the protection we needed in a chimney without the cost of a commercially made "box." We had been running a 6 inch pipe up the center of that, but it's ok to have this massively reduced temperature going out directly through the 8 inch. So, anyway, the opening in the burn tunnel is 7X4=28 sq.inches, the opening on the heat riser is 49 square inches and the opening in the pipe is 50+ square inches. So, that worked. I designed for 1.5 inches from the heat riser to the barrel top, but somehow it ended up 2.5 inches, so it's not as good a surface for cooking. That's ok - I have a cook stove. And since the top of the barrel can be opened, I figured out that I could get in there sometime and add some height to the heat riser and insulation to solve that problem - someday.
I used an old water heater tank to go around the heat riser, as an insulation surround instead of a cob and insulation mix. I filled it with perlite and then used some of the heat stop mortar to cover it at the top, making it level with the top edge of the heat riser. The firebox, burn tunnel, and base of the heat riser is made out of one inch firebricks. That is sitting on top of a row of two inch firebricks, with two layers (four inches) directly under the stove itself while there's one row under the whole barrel, which is sitting on top of a piece of cement board. I had to shore up the firebox with another layer of firebricks after I'd built it, so the firebox is now 3 inches thick. My brother cut off the water heater ends and the bottom of the barrel, then cut the square cuts out of the side to go over the burn tunnel.
The draw on this stove is simply fabulous. I finally figured out that I needed to start a fire in the thing with my crumpled up paper on TOP of the kindling instead of underneath it, because the draw is so completely down the burn tunnel that it was burning up the paper sideways without touching the kindling. By putting the paper on the top of the kindling, it burns DOWN to be pulled through the tunnel. Crazy. But it works. We've also learned now that after the fire gets going well, we can put a larger log in it as long as we keep a couple of smaller sticks burning alongside it. So, it takes a little longer between having to load the thing.
I also finally figured out how to build a bell next spring out of something I can afford. I'll be gathering a bunch of flattish granite rocks (well - grandkids will gather them) and build a big box out of them. A rectangle shape will fit in the space better than another barrel. I hope I can use fire clay. That would be a lot cheaper than heat stop mortar.
But, the single most wonderful aspect of the whole thing is spiritual. I feel like I'm sitting next to an outdoor fire pit when I sit in a chair next to my OPEN fire inside my house. Lovely. Simply lovely. It brings the outside in.
Just thought I'd share results since I had written in trying to figure out how to solve problems last summer. I DID it!
Lua - from one "old, handicapped, and still managed..." woman to another - WELL DONE!!! I loved reading your post, your discoveries, how you worked with what you had and asked for help/support when you needed it (and how your husband ate his words!! LOL).
Plus I just love to hear about ways people with "limitations" (physical, mental, emotional) make permaculture work for them.
You made my day.
Jen in Phoenix (blind in one eye, low vision in the other, severe pain most of the time).
Subtropical desert (Köppen: BWh)
Elevation: 1090 ft Annual rainfall: 7"
It sounds like you are more able than you knew and your home heating system is far above average
You should make your husband haul all wood and start all fires for a few years as penance for his reluctance to help. And be sure to rub his nose in it when showing it off to visitors. Then there's the ever popular "I was right dance".
Carefull on the bell sizing. If you are already at 150F° i wouldn't go over 24>26sqf internal surface area for the bell. I think this is if you have draft up the chimney. If your chimneys doesn't draw, may be remove 6 to 8 sqf ISA. A easier way may be for you. Find yourself a rectangular box, and dry stack the mass around it. Like cobbles, concrete blocks, pavers whatnot!
For rectangular boxes, a good source over here in France, is the equivalent of craiglist. I always look for home heating fuel tanks, or tractor fuel tanks.
Thank you, Jen, you in turn made my day with your response. I was poisoned by the medical mafia with their fluoroquinolone antibiotics, and the permanent consequences are joint, cartilage and ligament damage. Don't ever let them con you into one of the 17 brand names that have the word "flox" in it somewhere. It's pure poison.
Dale, he is already being quite gracious about letting me do the I was right dance - and already hauls most of the wood since I walk with crutches. Although, when I have to do it, I can with a harness I rigged up to pull a sled or wagon attached to my waist. The problem of course is that there will come a day when he can no longer do the level of work he does around here - hauling wood and water, taking out the sawdust toilet, fixing cars, finishing the cabin, feeding animals even though he hates my goats - a hundred daily chores. He wouldn't help build it, but since I was bullheaded enough to do it anyway, he is now delighted with it.
Terry, yes, it is saving wood already. I have today to compare to yesterday to see that. We're in this deep freeze here. I hadn't used the stove after the initial week of testing until today, because I had to shore up the firebox and was letting it cure for a long time before building a fire in it. So, for the past week of this freeze, I've been heating the cabin with the big bear sheepherder cook stove in the other room. It's amazing what a difference a little height makes. The room with the cook stove is 16 inches higher than the room with the rocket stove. When the cook stove is heating the place, the rocket stove room is always very chilly, but today we've had the rocket stove heating the place and both rooms are comfortable for about 20 percent the amount of wood going into the stove. Both stoves are close to the door between the two rooms.
Satamax, I didn't have a camera while building, so there are no pics of the process. By a sf area, do you mean sf measurement on the floor or sf measurement of the side and end wall? Or would that be cube foot? If on the floor, that's a bit more than the amount of space I have anyway - just a bit smaller maybe about a foot by 18 inches inside. That's a good idea about a metal box faced with rock. I'll check into it. The bell would be snug up against the stove barrel, then the pipe would be snug up against the bell. I've been wondering if there would be a problem with needing to insulate the pipe from the bell to prevent a draw problem.
It sure would be lovely to be able to buy that 4 DVD set, but the least expensive way (streaming) is 20% of my monthly income, so that's out. I seem to be doing ok with reading and online videos though. I think we might put a greenhouse onto the south wall of our house and I'm thinking about an actual rocket mass storage system in there, to also heat into the cabin. So many ideas about this wonderful technology.
Hi Lua. I didn't mean pics of the build, but of the finished product. I remember your pic of the room down a few steps. So i think i could see the change.
When i talk of ISA, it's internal surface area. Which means the added square footage of each of the walls, and ceiling of the box. Usualy, we don't count the floor, because it doesn't radiates much heat, due to convection.
I don't know what could be availlable to you, metal box wise. Toolboxes could be used, as i said all sorts of fuel tanks. Metallic lockers with the door louvres and holes sealed/welded. Even thoses army boxes, tho, they don't have a smooth surface, which means you'd have to cob between metal and mass.
Let say a 6'x2'x2' box has
3x 2'X6' so 36 square feet
2x 2'x2' so 8sqft more.
That's a total of 44sqft, a bit big. If you have draft in the chimney, you may be could manage. The only thing to avoid, is to have a cold plug, where condensation of gases stops the draft. Mind you, it's easy to test if your bro is around. Make the two holes in the box for the flue tubes, both at the bottom. then fit it on your system, do a burn or two, or three. If it doesn't stall, then your bell is good and you can proceed with the lining with stones or any kind of mass. (i'd rather use stuff which is square/rectangular, so the mass can be dry stacked, expansion and contraction of the metal would crack any joint between stones)
As for the bell, a scrapped electric oven has a squared off interior and is built for heat. Rip off the insulation and pile on the masonry. Or try this:http://donkey32.proboards.com/thread/904/simple-medium-mass-bells
Lua, I loved your story and I easily saw older me in you. I am neither old or handicapped. I keep my small well insulated passive solar house warm with a tiny fraction of the surplus wood my property provides and that is with an inefficient wood burner. So my set-up is sustainable. But I forsee a time in 30 or so I wont have the strength to lug a chainsaw all day, and lift blocks of wood on to the splitter, so in that sense my set-up is not sustainable. And thats where the appeal of an RMH is for me. I should be able to heat my house with twigs and branches. As long as I can bend over to pick up a fallen branch or maybe swing a bilhook and trim ny hedges I will have a warm house and fresh bread. One day when i am done researching RMHs I will replace my old belching airtight.
Fabulous work and my hats off to you and your husband.
The sun's a light bulb and the moon is a mirror-- Gord Downie