I'm advised that I need to make a post to prove to the PM system that I'm an actual human being. Investigating what I
should post
about led me to the PEP/Badge program, which further led me to the
Rocket Mass Heater forum. I've built a very small, but VERY functional
RMH which was used to heat a 16' RV through a cold winter six years back. At the time, I know I captured pictures of the build and
video of the heater working, but I've lost track of most of that. I'm going to try to go through old phones and such to find it (in order to earn
BB for my results), But I thought I'd start with a post about the build in general, and then add to it as I go. This means that I'll be describing something I can't yet show anyone, and can't "prove" my
project just yet; but I will! Also, I tend to be verbose. My apologies.
The story goes like this; my wife and I and our two young children were being forced out of the home we were living in, in the middle of winter, and our only immediate alternative was an old (1978) 16-foot
Class A Motorhome. There was no furnace in the unit as it had been stripped out years earlier by a previous owner, and I knew that with our finances at the time that it would be risky to try to depend on a heating unit I'd have to buy fuel for. I needed to be able to burn the small bits of
wood we would easily encounter almost anywhere we went, but I needed to do it with space and safety in mind. Space was more than limited, as you can imagine, and safety (we had a one year old) was paramount. I investigated ways to make this work, and settled on building a tiny
RMH. My initial research suggested that this couldn't be done due to issues of reliability and durability, but being both stubborn and intrepid (and at the time, desperate) I decided to try it anyway. Here were the problems; limited time, virtually no money, and few tools to work with.
Needless to say, we were significantly "downsizing", so we bartered and sold almost everything we owned. I traded an old video game system for a small flux welder (I suppose there might be a BB available for some of the work I did with that, too) and then set out to find the materials I would need to build my 'concept' stove. Nearly everything I ultimately used was salvaged from walkabouts through the general area. The base of the unit is an abandoned hydraulic fluid barrel (twenty gallons, if I remember correctly) I located at a long-abandoned former lumber yard. The feed tube and burn chamber I built by welding boxes out of an old bed frame I already owned and had cut into pieces. The tubes were scraps of heavy metal pipe, the larger of which I paid for (five bucks at the salvage yard) and the smaller ones I found at an old burned-out warehouse. The barrel I literally found along the side of the road; it was a small propane-type tank (think grill tank, but about half the size) that had contained some kind of medical gas IIRC. The "mass" was provided by railroad bed rocks that somehow found their way into my possession, with some sand mixed in. I also used some perlite from my wife's
gardening supplies, and post-setting concrete I purchased (one of the few cash outlays). My total cash spent on the project, including the welding wire, was less than $30.
The tricky part was the chimney; how to build one within an RV, in very short time, that would be both cost effective and effective-effective? I finally reasoned that I could widen the area where the original furnace had exhausted (through a side wall of the rig) and run heavier-gauge metal from the heater through the wall. From there I would attach and detach a flexible
dryer vent on an as-needed basis. I reasoned that by the time the exhaust from the RMH hit that, it should be cool
enough to not be a problem, and from a design perspective the thing should draft the same as any fixed system. I built a double-wall pipe from the heater to the wall using different sized cans left over from dinner (a bean can and a soup can, I seem to remember) and fitted the dryer vent with wire hanger supports that ran it up the side of the rig to the roof.
I enclosed the entire unit in a cabinet/cage I constructed around it specifically to keep the baby away from it altogether. In it's entirety, the whole shebang took up the space of a small refrigerator (bigger than dorm size, smaller than "medium"). I could open the small cabinet door to fire it and clean it, and open a panel in the door to feed it. That system worked perfectly, and despite the significant heat the unit put out (and how hot the barrel got) it never made the hardibacker I'd surrounded it with all that hot. I tried to be super-careful with clearances, but used the cement board for extra safety.
Please note that I realized there were some potential safety issues with this design from the outset. I mitigated all of those to the utmost (I'm notoriously safety-conscious, especially with fire and ESPECIALLY with a toddler running around), and I kept a commercial-sized fire extinguisher and two smaller ones within arm's reach of the whole thing. Of course, in a 16' box, EVERYTHING is within arm's reach! I promise, I made it as safe and "fool-proof" as it could possibly be.
The concerns were "will it burn", "will it ROCKET", and "will it last"?
The answer to all of those things was "yes". In fact I still have the heater in storage, though I sold the RV several years ago. We were fortunate enough to put off the move into the RV until February, so we didn't have a long winter to grind through, but it still got plenty cold for a couple of months. We burned literal sticks that we found along the side of the road, within parks, etc. I could keep the whole cabin toasty for the night using wood that in total amounted to a piece the size of my forearm. When the heater really got cranking, it was a marvel.
It was not without issues; the chimney was insufficient in design because it didn't allow me to "cheat" when drafting was an issue, and the unit back-drafted twice, filling the cabin with smoke and sending us scurrying for the exits. Both times it was especially windy. Had I needed to use the heater for more than just that couple of months, I would have re-thought the removable chimney concept and built something better, but as it warmed up and we needed the heater less, that fell to the back burner. Ultimately we were able to move from that smaller unit into a larger one that had it's original furnace, and the RMH was placed into storage (where it remains to this day), but now that we've purchased a homestead and I have a bunny barn to heat, it's likely to see use again this upcoming winter. With a permanent chimney, of course.
I have pictures of all of this, including at various phases of the build, and video of the heater in action. I promise, as soon as I find them I'll post them in this
thread. I must tell you that I was discouraged at first, being told by multiple people that a small RMH simply wouldn't work. I'm here to tell you that it WILL. I can't say with certainty how long it will last; I suspect the firebox will eventually burn out (though mine is also surrounded/insulated by a perlite/concrete mixture), but for occasional use and especially for the cost, I cannot be more pleased with what resulted from this first-ever build. I also learned to grind and weld as part of the project (well--something resembling welding anyway; don't judge) so that's a bonus.
I'll go look for those pics and videos.
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