first thing that came to my mind (and food for your creative brains):
An integrated shaping tool for the mound on the lower side of the swale (after the actual digging tool).
Might be useful especially for steeper slopes tp prevent excavated material rolling down the hill.
Maybe even with a slight compacting device to stabilize it in place.
Reading this thread I immediately remembered this solution of a German enigineer, but it´s only viable if you go large scale, and by this I mean very large scale.
Find an area with massive uncracked bedrock, cut a very big cylinder into that bedrock (the techniques to do that exist in other industry sectors, mainly mining and quarries) , seal it on the sides and lift it by pumping water underneath.
Most information about the concept is in German, but there´s an explanatory article in English HERE
There´s a guy with the nick Manuel over at Donkey's who had the same idea independently and uses it in his builds, but he cuts the pipes by eyeball, which is ok when he cobs them in.
Cutout template rolled around the barrel is 44 cm / 17.5 " wide and 15 cm/ 6" (system size) high, circumference/edge length approx 1 meter / 3.3 feet.
More important to me was the intersection depth that is 11 cm / 4 1/3 " (depth 0 means tubes touch but do not intersect).
The nicest thing about this I discovered: when you open the cleanout you can see straight through to the bench entrance an clean super easy if necessary.
And since the combustion unit is mobile you can hook up the thermal battery left or right depending on where you install it.
The build sequence isn´t published yet, I plan to do so here and at Donkey's, but it will take some time. I want to run the stove for some time and get used to fire it under all atmospheric conditions before I declare success.
Here´s a pic of the finished unit. Flue pipe ends sticking out behind the barrel to the left and right not visible here:
Brief explanation: a rocket combustion unit on wheels and not much room at the back side of the barrel.
Idea: Intersecting the barrel with the flue pipe. Pipe runs tangential and opens where it cuts the barrel.
Advantages: bigger open space and less direction change of the exhaust gases compared to a 90 degree outlet. One of the side openings is the flue connection and the second is capped as clean-out.
Challenge: get the intersection cut to fit. Solved with an Excel template calculation sheet.
Pictures:
Printout of the actual intersection, according to theory:
Checking my math with cardboard tubes, you should get the idea by now:
Template cut out and layed on target area at the actual lower barrel part, 2" above floor for ash deposit space:
Tubes cut (jigsaw), matched, secured with screws and sealed with high-temp automotive silicone (lack of welding equipment):
Opening viewed through the exhaust/cleanout pipe:
Metal "manifold" with cutout for core:
Transition space viewed from the inside:
"Manifold" in place:
Being built in with cob mortar and perlite/clay insulation:
The finished heater is running its exhaust through bell bench in the 4th week now with no hassles.
- UPDATE 2019 -
This manifold works beautifully, doesn´t restrict the gasflow at all and doesn´t clog with ashes, J-Tube workshop heater still going strong into the third season.
Here in Germany there´s company that produces basalt fibres for composites, they sell their "waste" cut to 2.3" for cheap. Maybe there´s the same where you are if you google it.
Hi Glenn, great build !
From the drawings and pictures it seems you actively cool the upper part of the feed tube by channeling the air for the p-channel around the metal collar that´s sticking in the feed.
If I´m right, how well does that work, and does the plate next to the feed still get hot enough to cook some tea on it (as there is a small kettle there) ?
my first thought was: Leave the outside barrel faces exposed, looks like a happy home !
Kidding aside, the main problem would not be the heat conduction of the steel itself but the air enclosed that can move freely and start a convection loop inside each barrel.
It will charge heat from the inside face, rise, move along the top and give it off and cool and fall down at the outside face of the barrel.
To counteract this you´d have to fill every barrel with something foamy aka additional insulation.
Wether horizontal barrel walls could be load-bearing and support a roof I don´t know, but your drawing shows the edge reinforced by something else that holds it up so that´s fine.
I also think that cool metal attracts condensation of air moisture and might cause straw that´s suffed in between to rot, but I´m not sure.
I´m just about to finish one in northern Germany, I´m investing every bit of free time to get it lit before the next cold spell.
I dealt with the laws in two ways: Since it´s my first one for testing it´s not in a house but in a 2 room brick workshop that I want to keep warm.
And since all the laws and restrictions refer to stationary fireplaces ("ortsfeste Feuerstätten") I built the combustion unit on wheels. This way it´s more like a big barbecue oven
Here´s a pic of the combustion unit that can be rolled around.
Already tested without mass and working like a charm.
I documented the build with a lot of pictures and some videos starting with the chassis, I hope to put a Youtube video up once the thing has proven its functionality.
The thermal battery however is fixed.
SInce I discovered this kind of heaters I´m totally nuts about them, got both books (Ianto Evans and the Wisners) and Pauls 8 DVDs.
And I´d be happy to connect with other RMH builders in Germany. Maybe there´s a way to get them established here.
And even though my first heater is not completely finished (I just started to mortar the bench after a lengthy chimney liner install) I´ve got the second already planned in my head. This will be more of a micro batch rocket instant heater without mass, for sure on wheels again.
yesterday I watched a longer Youtube video about earthen plasters. The guy managed to darken his clay plaster by mixing in finely ground coals left over from his wood stove. Looked good, dark but not pitch black.
This could also be applied to tromb wall plaster.
I will leave the evaluation if your new design will work to someone with more practical experience under his/her belt.
My feeling is that the top gap would work better with 50 mms /2 inch (it´s not only the cross-section needed but also room for the direction change of the gases).
And if you could somehow construct a round or at least octagon heat riser in that square tube it would leave a little more room for the gases to stream down on all four corners.
It would not harm the upward draft through the riser as long as it´s got 75 mms inner diameter
Scott, if you have room for a footprint of approx. 30 x 50 cms I have got an idea:
Your heat extraction bell can be a capped standing steel tube (with removable top lid /cooking plate in case of inspection) of 30 cms diameter, about 1 meter high or more.
Cut an opening low on the side to fit in a rectangular box-like tube of steel plates which protrudes towards the inside of the big tube as well as towards the outside.
The box should be just big enough to contain a small (4 inch /10 cm) batch box (maybe cast of refractory concrete with thin walls) wrapped or embedded in refractory (and shock absorbing) insulation.
Heat riser could be made of 5 cms /2 inch refractory fiber blanket fitted inside a 20 cms / 8 inch diameter steel tube which is fixed near the rear inner wall of the big tube (viewed from the opening of the fire box).
This way you will further shorten the required length you need for the batch box by "shoving" it deeper into the big tube.
Then you only need a door at the front of your batch box "insert" and that´s it.
You´d only have to watch out that there´s enough space to the left and right of your inserted box so that the gases can pass it unhindered on their way down to the exhaust opening.
This would be basically a shrunk version of Peter van den Berg´s workshop heater made of three full-sized barrels stacked on top of each other.
It can be found here.
there are several reasons why your current heater configuration doesn´t work properly:
1) the recommended ratio of the lengths of feed tube, burn tunnel and heat riser are 1:2:4, So your heat riser is way on the sort side.
2) the area around the heat riser where the gases must come down again seems very narrow, normaly the minmum gap should be 2 inches / 5 cms all around. Not to forget a big enough top gap between riser and ceiling for the gases to turn direction.
3) the use of metal to contain the burning fuel has serveral disadvatages:
It conducts heat away from the fire, thus cooling the burn and limiting its efficiency.
Due to this the feed tube will also heat up and serve as a competing chimney causing smokeback.
With an unsinsualted heat riser the metal wil also conduct heat between the inner (upwards) and outer (downwards) exhaust gas path, so the heat riser gets less hot and produces less updraft and the surrounding chamber gets hotter and produces less downdraft.
If you manage to get hot and clean rocket combustion by insulating the burn area form the outside, metal will spall and disintegrate over time.
However metal is fine as a casing around an insulated burn tunnel and heat riser made of refractory materials,
I understand well that it´s tempting to construct a rocket stove with the materials you have at hand, but if you want to heat with very little wood and no smokeback and a clean exhaust you´d have to redesign your stove qite a bit.
First thing would be that you construct your feed, burn tunnel and riser of firebrick splits. There´s a mock up for a small fire brick core and heat riser that I found very nice in the first few minues of this video
This fire brick core should be wrapped either in cermic insulative fiber board or put into a bigger metal tube that is backfilled with a mixture of 1 part fireclay and 3 parts Perlite, both serving as insulation to keep the combustion super hot and clean.
Also such a " soft insulation" will protect the firebrick core from shocks while driving with your van.
And the radiating casing around all this should be big enough to not restrict the downflow of the burn gases.
Thanks Peter, that´s exactly the way I planned to do if if it will be the bell bench.
My main concern with this is the condensation interacting with the cob mortar, especially at the bottom.
On the other hand, having your expert opinion and avoiding to buy new duct pipes ist tempting !
i´ve got a bunch of questions concerning the use of concrete pavers for a RMH bench.
The bench will be situated in a rented workshop shack. Normally you think of instant heat for a workshop, but I can play music in there without disturbing anybody anytime so I like a bench that stays warm, also for the benefit of dry tools/machines and glueing wood in winter.
So conditions are that the bench shoud be removable with reasonable effort if I move out one day, and I gathered lots of concrete pavers (urbanite rocks) for the thermal mass. It is planned to be simply rectangular.
My initial plan was to construct the bench as a hollow "bell" mortared and sealed with cob (see cross-section-pic).
My worries with this are:
* Is the single seal of a cobbed gap safe enough ?
* Will I be able to resoak the cob mortar in the small but wide gaps between the pavers if I have to dismantle it ?
* And the main objective: If it´s cool and there will probably be lots of initial condensation from the exhaust, will this water puddle on the bell floor and/or soften the cob mortar and spill out ?
So I stopped to rethink the plan and came up with another solution that uses a flue run with a 180 degree-turn at the far end.
Coss-section plan looks like this:
Plan for this is to loose-stack all the pavers (except for the bricks at the top that will be cobbed in) for easy and quick assembly and dismantling. Questions:
* The pavers got a rough surface of embedded stones on one side, will the little air gaps between them harm heat conduction ?
* What will be the best infill directly around the duct ? I was thinking either to use pebbles (insulation issue ?) or to use a cob mixture that is more on the sandy side.
Any thoughts & comments which way to proceed are highly welcome !
Just wanted to share some interesting videos of obviously working RMH's that were recently put up on Youtube.
Why am I sure they're working ?
Because in both cases people are skilled and they reference Erica & Ernie Wisner's Rocket Mass Heater Builder's Guide and Paul Wheaton's work as their source of knowledge.
Enjoy !
Workshop batch box heater of beauty:
And an interesting follow-up on sustainably growing RMH fodder:
I can recommend the Website of Mathias Wandel.
I find it´s kinda porn for woodworkers (and also has valuable content for beginners).
It contains a lot of very practical tips, recently there was an article on how to self-build a low-tech lathe.
All documented very well on video.
He got famous for selling plans on how to build band saws made entirely out of wood... now you can DIY almost all known woodworking machines as wooden versions from his plans.
Concering dovetails, I´d go for fine box joints, much easier to make and there´s also a video on this site where he compares the strength of both, and the box joint wins.
as I looked at the pictures in the project website another idea come to my mind:
As well as preventing too much melting by applying shade or insulative covers, you can also speed up the melting by covering parts of the Ice Stupa with fine dark dirt, in case more water is required.
well, this is new territory, I suppose no one has tried this so I can´t say it it will work.
What I can definitely say is that if a forced air system breaks down in the middle of a burn, may it be because of mechanical failure or a power outage, you will be in trouble.
Even a small amount of smoke back into an enclosed room is already very nasty.
as I read this split-run-challenge I spontaneously began to do some math:
One 6" duct and four 3" ducts do have the same CSA, however the wall length (circumference) of four 3" ducts is double to that of a 6" duct, hence I assume double the drag per run length.
If you subtract a boundary layer of say 0.2 inches the ratio between the circumferences gets somewhat better, but the "flow-open" CSA of the 4 ducts becomes smaller than that of the 6" duct.
At this point I would say "try, but with a fan", but it gets worse:
Suppose you have no forced air supply double drag means half the recommended maximum run length through the mass, for a 6" system that translates to 22 1/2 feet instead of 45 feet straight run, no bends.
Divided by your four runs you have 5 1/2 feet per run, straight, without any bends. But if you want to heat four rooms and channel these short runs into a room and back to a combined chimney you will have to subtract substantially more length from each run for the required bends
At this point I would say: IMHO not possible.
But please correct me if my logic or math is wrong.
since I missed Pauls DVD-Kickstarter I´m backing this one ! Thanks for the link !
I already drew invaluable information from Ernie and Erica in this & Donkeys forum and in some podcasts, so it´s time to give a litte back As a consequence I will be lighting the fire in my first build (and hopefully not the last) tomorrow evening... but this will be subject of another thread to come...
