I'd like a Rocket Mass Heater and I need an oven. RMH is a semi-permanent and heavy item. I'm not at a moment in my construction phase where I can install something like this, mostly due to the fact that I am cold now and I would have to rebuild/regrade and otherwise do very highspeed Herculean things which I am not currently excited to do. My thought is to build a simple drum can oven which is currently prototyped and working in the yard roasting pork belly and pizzas which I am generally excited to do. My thought is just to transfer the stove into the concrete floored area of the house mostly the way it is but with the addition of a red brick rocket feeder underneath to raise the combustion rates as well as an exhaust that gets everything outside. I'm sacrificing a lot of heat and getting very little thermal mass retention this way. So - imaging a drum can on its side about 2.5 ft off the ground with a brick rocket feeder underneath and a 6 in exhaust coming out the top... any thoughts on creating a mass to dump some of this heat into?? the mass must be non-permanent (so no clay or poured concrete) and cheap and not too labor intensive (I'll do digging, carpentry or minor masonry).
I haven't thought of anything except experimenting with a thermal coupler and water... The exhaust which seemingly needs to go up and away in this case I can't figure how to capture... although it is conceivable that the exhaust could be wrapped with some kind of heat absorbing material for this purpose.. I think the stuff I want is only in laboratories... like something lightweight and formable with good heat retention, flame resistance and inexpensive.. what I'm imagining would be like something with the thermal mass of water and the physical mass of styrofoam... that'd be damn cool.. Anyway they don't have any down at the local Juntendo here in Etajima, Japan. but I'm game if anyone has thought on how to capture more heat... The only thing I can easily do is fill the burn chamber, which is quite large, with Kawara (traditional clay roof tile) which Is available and portable etc... I cook on it as well... Thanks!
Oh and for anyone who is a philosopher and a mild masochist I repeat this quote from I know not who, "Nothing more permanent than a temporary solution". Yea I'm lining myself up for that. HAHA
Is your current firebox inside the drum/oven? Are you hoping to run the rocket exit through the oven space? I don't believe that would be safe for use indoors if that is what you are talking about, so some clarification is in order.
If you want to run the rocket exhaust around the actual oven space in a sort of double boiler effect, that would be safe and effective.
I would build your rocket burner of brick with fine clay mortar - pure ground fireclay would be ideal, but any decent clay screened to remove anything larger than sand would work. A smooth potter's clay might be easy to get if there is a studio near you. The clay will not act as glue to hold the bricks together, but as a filler/sealer to make sure there are no air leaks, and it will come apart easily and cleanly when it is time to build something else.
Any stone or brick/block that you can stack around your barrel would work for quick easy heat storage. If you build a box to hold it, you can surround a horizontal duct with gravel and rock. This is not as effective as a solid cob mass, but is easily alterable. See Paul Wheaton's pebble bed RMH for an example.
Location: Hiroshima-shi, Japan
posted 3 years ago
Thanks for having a look, apologies for lack of clarity.. the stove goes in a large high ceiling room (peak of 8 meters) over a concrete floor which is in poor condition(so I don't care about what my experiments do to it). from the floor there will be a brick feeder, so like a stack of bricks maybe 8 courses high with a vertical hole in the middle to match the exhaust pipe capacity, feeding horizontally from down low. Above this will be a hole in the bottom of a drum can laying on its side. inside the drum can I'll put a bunch of clay roofing tiles as heat sinks and also to act as a deflector plate to send the flames and gases coming from below out to the sides in order to create more travel distance/baffling . The tiles are curved and I'm working on optimizing the movement of the current in order to get the best velocity. then there is an exhaust pipe coming out the top which right now is just a 5 inch round chunk of tube a little better than a meter long(the stove is outside right now...) I haven't decided on 6 or 8 inch pipes for when I bring it inside, although more $$ I'm thinking the 8 inch pipe will be more useful for a more permanent install later.. but am open to suggestions. The image shows the location of feed and exhaust which are far to the back which was not planned but rather just location of the holes from a biochar retort function. I could get a new drum can. I think this location of ins/outs is probably less than optimal as it sends some of the flames straight up the back wall making the exhaust rich.
If your oven space is in the smoke path, you are going to risk major smoke in the house when opening it to add/check/remove food. Using the 8" chimney going up through the roof will give strong enough draft that you may be able to keep negative pressure in the oven so room air mostly gets sucked in rather than smoke puffing out when opening the oven door.
I still would strongly advise a smaller barrel or other sheetmetal chamber for the actual oven so you don't have to worry about this. The tile baffles are a good idea in any case, especially if you can arrange them so they direct much of the hot gases forward and keep them from short-circuiting. How large of an oven cavity do you really want?
Location: Hiroshima-shi, Japan
posted 3 years ago
Hey! What do you think of reducing the oven space via some clay bulk? I'm mostly hoping to get something that will burn a lot of refuse wood and be manageable enough not to kill anybody. I don't expect to use this again after this season as I am repairing adjacent spaces. Right now we have a poorly insular space and literally multiple tons of scrap and we're burning Kerosene to heat it.. The simplest way to shrink the space without difficult acquisition/production process would be to add mass to the chamber. I'm ok with a bit of smoke as we have vast overhead space and I am sure once the draft begins to pull we'll be clear. It sounds like you like 8" better. Also I need to create enough draft without going up over the roof .. I know RMH often don't need to. my outer roof height is over 10 meters and hell to get to.. think multiple Japanese clay rooves..