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| [+] rocket mass heaters » RMH to heat a garage (Go to) | Satamax Antone | |
This is essentially what I built in my garage...6" standard rocket core with a water heater tank as a bell. Didn't have room for a bench, so it's designed to just extract as much heat as possible. It's a very powerful heater. It can raise the temp in my (very poorly insulated) garage about 10* an hour. When it's below freezing out, it maxes out at about 70*F...at which point I'm melting the snow off the roof lol. Using a fan to circulate the air around the garage helps, but if you had a standard ceiling with any kind of insulation it wouldn't need to be very big. It was kind of a big project...it required a surprising array of my skill set. Very happy with it though...I got a ton of heat in my garage burning scrap wood and stuff people would usually toss in their burn pile, so I got heat for "free". Here's what it looks like right now...  |
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| [+] rocket mass heaters » Materials (WARNING novice question/potential stupidity) (Go to) | Satamax Antone | |
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Wow...that's a 500 gallon tank (!). Would make a hell of a bell if you had room for it...if you had room for it lol. I made a bell out of an old 50 gallon water heater (seen behind the barrel). The one you posted would have 10 times the internal volume. Cut it in half, and you've still got five time the volume. I would think the biggest problem would run into would just be moving it around and working on it...those things are usually set into place with a small crane mounted to a big flatbed truck.
The rounded top shouldn't have any effect on function I wouldn't think. The gasses inside should still stratify as they would if it was flat. |
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| [+] rocket mass heaters » feed tube height (Go to) | Wyatt Barnes | |
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I cut my wood pretty short...about 12" or so (for the most part). I know a lot of folks have an interest in getting longer burn times out of a rocket stove, but it seems like you might be kind of fighting against the nature of the beast... There's more to it than just having longer pieces of wood (IMO, anyway)...it seems like as the wood burns I have to do a fair amount of "adjusting" it's position in the feed tube to get the airflow just right, in addition to adding more wood. Building a batch box instead of a J tube could be a more workable solution... But, you never know until you try I...build a prototype, and share your results, I'm sure a lot of people would be interested to see if it works.
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| [+] rocket mass heaters » dont do's? (Go to) | shilo kinarty | |
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Don't try and burn wood that's too long--if it gets jammed up on another piece of wood, the bottom can burn out, allowing the now top heavy (and flaming) remains to tip over onto your floor. I cut all my wood to about a foot in length, though I know others run wood longer than that.
Don't install it too close to combustibles (or use a heat shield). Follow NFPA guidelines for an unrated wood stove, and you should be fine. Otherwise for the most part it's I think it's about like running a regular wood stove...use common sense that would be appropriate for something that gets really hot. I keep my welding gloves handy for when I have to re-arrange the wood in the feed tube. |
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| [+] rocket mass heaters » solar vs RMH (Go to) | Scott Clark | |
One of the things I like about burning wood for heat is you're releasing carbon back to the atmosphere that's been stored for what, 20 to 50 years maybe? Much preferred to the eons old carbon being pulled out of the ground, IMO... And if you're burning fuels off the property, you'll release far fewer pollutants than if they were consumed in a wild fire...every year we have to live through a smoke filled valley during fire season. A forest fire is not exactly a model of efficiency lol. And as others have said, a properly running rocket stove won't smoke at all once it's up to speed...the smoke is fully consumed by the fire. Even carbon monoxide should be pretty well burned up. |
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| [+] rocket mass heaters » Is a 2" riser a ridiculous idea - given that I want a really low output? (Go to) | Scott Clark | |
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It sounds like your best bet might just be to put another pellet stove out there... I have three pellet stoves to heat my house, but the garage is heated with a massless rocket stove. I actually have another pellet stove I could have installed out there, but I wanted to burn wood because I can basically get it for free. A pellet stove takes up a lot less room than a rocket stove, if space is an issue. They also have much closer installation clearances (many of them only need a few inches of clearance from a combustible wall). They can also be run off a thermostat, and don't have to be fed every half an hour like a rocket stove. Set on low burn, my big Avalon might be able to squeeze two days out of a full hopper (about 80 pounds of pellets). That's with a constant burn that never shuts off. But, since it can run on a thermostat, that may not even be necessary.
Anyway, just a thought...rocket stove isn't the answer to every heating situation, but you may definitely find one it's a good fit for  . |
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| [+] rocket mass heaters » if it burns hot enough why not burn cedar and pine? (Go to) | thomas rubino | |
Yea, it's really interesting to see the different perspectives people have just based on where they live... I'm going to try and clear my 5 acres of all the deadfall in the spring/summer and process it for rocket fuel, which has an added bonus--fuel reduction across the property in case of a forest fire. In 2012 the Sawtooth Fire came within a mile of my house (it was in the evacuation zone). I've got Ponderosas all over the place, and at least two dead ones I need to cut down (and make into fire wood). Rocket stove should love all of it. This will probably make some of the folks back east laugh... In this big pile of scrap wood I got for free, there was a single oak plank...it was grey and weathered and I didn't recognize it until I cut it. I handed it to my kids so they could see what a fresh cut piece of oak smelled like...they all wanted to keep a piece like it was something exotic from some foreign land lol. I have about 25 pallets out back I need to dismantle, and in them I found a single one made entirely out of oak...I put it in the woodshed, and I'm going to take it apart and use the wood for something other than fuel. The beams are these nice thick pieces, which seem like they should be useful for *something*. Maybe carve wooden swords or something. Next summer I promised my kids we'd try and make a Viking shield (we do some nerdy projects like that)...we'll forge the boss from a piece of steel in our pit forge, and I figured the oak planks from that pallet would work just dandy for the rest of it. So much better than pine . |
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| [+] rocket mass heaters » if it burns hot enough why not burn cedar and pine? (Go to) | thomas rubino | |
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Interesting...the idea of burning hardwood is almost completely foreign to me lol. Around here oak is almost unheard of...there's some maples in town, but out where I live it's all pine...with some fir and aspen mixed in. And the occasional random apple tree. If you run into a piece of oak, it's probably part of a piece of furniture
. Everything I've run though the rocket stove so far has probably been some variety of pine...not knowing what a piece of hardwood burns like, I guess I don't know what I'm missing lol. It does burn pretty fast, but what the heck...all my wood so far has been free, so I can't really complain about how fast it burns. It's hot and clean too...inside of the heat riser is nice and white. |
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| [+] rocket mass heaters » fire science: demonstration of smoke burning (Go to) | Guerric Kendall | |
Yep...back when I was an HVAC tech, once in a while we'd get someone calling complaining about their (insert whatever heating appliance here) making soot in their house. First question we'd always ask was... "Do you burn a lot of candles?" The answer was yes almost 100% of the time. It was only an extremely rare case when they had soot in the house that wasn't caused by them. |
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| [+] rocket mass heaters » What is the best way to grow fuel for an RMH (Go to) | Julia Winter | |
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This has been a really interesting read... I've got 5 acres with a lot of Ponderosa Pines on it, and next summer I'm going to collect all the dead fall from the property and process it for fuel. I'm lucky enough that around here there's so much waste wood (and free scrap if you scrounge) growing trees just for fuel probably won't be necessary any time soon. I figure once I get all my own dead fall cleaned up, I can always go collect it from public land around here if need be.
Fun to read about other options though! |
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| [+] rocket mass heaters » ash the byproduct (Go to) | Peter Ellis | |
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Mine doesn't have an ash pit...I just put on a glove and stick my arm into the core and scoop it out. I have three pellet stoves, and thus lots of empty bags...I just keep one handy and put it in there. I don't keep it running constantly though, so it's not hot in there when I clean it usually. My barrel lid is also removable for service...a shop vac will clean out anything in there really easy with the lid off.
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| [+] rocket mass heaters » First build of big RMH - first test problems - need ideas and feedback (Go to) | petra sips | |
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I'm sure people with more experience will chime in, but here's a couple of thoughts...
Do you have an external vertical chimney? Is it long enough? If not, back drafting could be caused by something in the house using your rocket stove as a place to draw in makeup air (like a dryer or bathroom fan or something). Also, it sounds like you might be having an issue with your heat riser...if it's not insulated well enough, the temperature will equalize between the inside and outside of it, at which point it will stall. Also, is it tall enough? If you're not getting very good velocity through the feed tube, you can also cover it partly with a brick to speed it up, but if your heat riser is the issue that won't be much help. Also wondering if the transition out of the barrel is big enough...it might be choking the whole system. Anyway, if it will run for a while and then stall, your heat riser is probably the first place I'd look...once a draft through the system is established, it should only get stronger as the core (and more importantly the vertical vent) get hotter. Anyone else? |
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| [+] rocket mass heaters » Heat riser material (Go to) | Geoffrey Levens | |
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I'd add a couple other thoughts to the cast riser... My own experience messing around with this stuff was that you need to balance the amount of clay (binder) to the perlite (insulator). Too much clay and it's not as insulative...not enough, and the whole thing will be crumbly and unstable. You can add furnace cement to the mix, which will stabilize it a lot once you fire it. You can also thin the furnace cement with sodium silicate to make it easier to mix in (and the silicate will also make it stronger when fired). I'm also working on a whole new type of insulated riser that will hopefully be easy to make, light weight, super insulated, and (relatively) cheap... Should have details in the next month or so...
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| [+] rocket mass heaters » I think I have RMH insanity (Go to) | Jay C. White Cloud | |
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Couldn't agree more that experimentation is the mother of progress...and half the fun of building these things is trying things out and learning...props for thinking outside the box. I do have to second Als suggestion to keep a fire extinguisher handy...if your core is insulated well enough, it's probably only a matter of time until that OSB dries out enough to catch fire...and since it would be inside the exhaust you probably wouldn't even know it until it was falling apart (and on fire). Years ago when I was an HVAC tech, I saw some installs that did work fine for a while, but were time bombs. Things like people putting tile up behind a wood stove and ignoring the clearances listed by the manufacturer...looks and works fine, but they couldn't see the wood behind the tile slowly pyrolizing from the heat. Another time I had a huge shop building so full of smoke we all thought the building was on fire...but it was actually the wood stove back drafting because the chimney they put in wasn't tall enough for the conditions they had. If that had been a residence and it happened when the people were asleep, they'd be dead from the smoke and CO. I'd hate to see anyone on this forum (or anywhere else) get hurt because of their rocket stove. There's no reason you can't do a build on the cheap and still meet basic safety requirements...my entire heater was built with stuff sourced from Craigslist and used building material stores (or stuff I fabricated from used parts). Only new stuff I bought was fireclay, perlite, furnace cement, and some consumables like welding wire and cutoff disks. Saved hundreds.
Anyway, best of luck, and stay safe. Don't be a marshmallow...or a newspaper headline. |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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Hey guys,
Just thought I'd give one more update on this thing... Stove has been running great...will raise the temp in the garage about 10* an hour until it hits about 70...at that point the garage is leaking so much heat the stove can't seem to get it any higher. My roof is plywood covered by two layers of asphalt shingles and finally a layer of steel...after about 4 hours I'm melting the snow off lol. Next project is going to be hanging a bunch of R21 bats up there I think. The stove is a seriously powerful heater, but it would be nice if I could get it up to temp and then start directing more of that heat into the ground level of the house... Anyway, thought I'd share the results of another experiment I did with the stove--I added what I'll call a "heat scavenger" for lack of a better term (far as I can find, nobody else has done this exactly, so I guess I get to name it lol). The old water heater I'm using for a bell was originally gas fired, and so it has a 4" flue pipe running square through the middle of it, with this swirley metal insert thing that was originally supposed to slow the burner exhaust so it would heat the water more efficiently. So, my idea was to use a blower to force air back down the heat exchanger (reverse of what it originally did) and blow the heated air back out into the room...thus scavenging more heat from the bell before it's dumped out the exhaust flue. I had a 115CFM blower from another project that I used...I cut and welded a flange to a piece of 4" B-vent pipe and elbow, and attached the whole thing to the top of the bell. Also cut a piece of black iron gas pipe and welded it to the bell to act as a support for the pipe so the elbow isn't too stressed. I should have tried to find a better piece of pipe..that one was pretty rusty inside, and was almost too thin to weld. Poked a lot of holes in it lol. Oh well, it's strong enough to hold, and the extra holes got plugged with high temp silicone. Oh, and I also added a solid state motor controller so I could vary the speed of the fan. Here's what it looked like when I finished it:
Yea, I know...it looks like I stuck a turbocharger onto pieces of an old steam locomotive. I kind of like the look actually. At least out in the garage...not sure I'd want this in my living room lol. How'd it work? Here you go... 
Once the stove is up to temp, it'll pump out air at a consistent 115* all day...and it's got pretty good flow. Not sure how much of the 115 CFM I'm losing, but it does pump out a lot of air. Unfortunately, there is no free lunch...the down side? It's loud. Like really loud. Like I don't want to sit at my workbench next to the rocket stove while it's on. It's brutally efficient, but it sounds a bit like someone left their F105 running in my garage. Best use I've found for it is just running it when I've opened up the garage to let the heat into the rest of the house, and the noise doesn't matter. Turning the speed down doesn't help as much as I'd hoped. All the surfaces around there just reflect the sound, so it's less but not by that much. Kind of too bad since it works so well. On the bright side, it pops right off when I don't want to use it...and I can go with Option B: sticking a piece of straight pipe on it. It acts sort of like a mini-chimney, using natural draft to get the heat to rise up out of the bell. A bit like venting a chimney into the room. It won't work like the blower, but it's better than nothing, and obviously it doesn't make any sound. Anyway, just thought I'd share the results if anyone else was thinking of doing something similar... |
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| [+] rocket stoves » Fire brick or cast with fire clay? (Go to) | Richard Dawson | |
Thomas--if you ever need more fire clay, it might be worth a trip down here to Hamilton...Donaldson Brothers has Lincoln 60 for $7 a bag. I bought the last of what they had, but they were looking to get another pallet in, so they've probably got more by now. Josh--I'll echo everything else that Thomas said... I went with a brick core, and being able to play with them like legos was a big help in finding a configuration that would work well with my setup. I also cast my heat riser...12" sonotube for the outer form, 6" steel pipe for the inner. Wish I could have found one of the small grease barrels, but apparently they're just about impossible to find (around here anyway). For the heat riser mix, I followed the recipe I found on another forum...fireclay dusted perlite, mixed with furnace cement thinned with (home made) sodium silicate. I filled about half the form on my garage floor, and the other half with it stuck in the barrel. I had to put it in there by myself, so I wanted to get it in before it got too heavy/unwieldy. It took about 4 hours of burn time to really cook the sonotube, and even then it's only about the top 2/3 of it that cooked off. I also made a "hot face" of fireclay/sand at the top as a sort of "cap". When I started out I was temporarily using a piece of insulated Class A chimney (which worked fine), but would really start to lose it's draft after about 3 hours...I think the whole thing was heating up to the point the temperature differential between the inside and outside wasn't enough, and it would start to stall... Even after 4 hours, the draft on the new insulated cast riser is just as strong as when it's getting going, which I think shows just how well insulated it really is. Good luck with the build! |
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| [+] rocket mass heaters » Looking for Rocket Mass Heater Designer/Builder for paid build in Bitterroot Valley, MT (Go to) | Scott Clark | |
I'm up west of Hamilton...but I'm not an expert, and I'm not really in a position to help on a project right now...but they've got my moral support . I will say that they may want to wait until spring to start their build...I was putting silicone on my chimney flashing literally the day before we got our first decent snow of the year... I did most of the design/building/experimenting out in the driveway...at least in my case it would have been pretty much impossible to do it this late in the year. If they have enough workspace it might be possible... And I gotta say, it was really nice being able to build a working mockup outside so I could work all the kinks out before moving it inside. I did all the cutting/grinding/paint stripping/welding/painting/etc outside...in the end I was able to just do the final assembly in the location it's in now.
I do wish them the best of luck though...glad to know I'm not the only one down the Bitterroot doing this stuff . |
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| [+] rocket mass heaters » RMH design for safety and code compliance (Go to) | Bill Bradbury | |
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That looks like a direct vent gas flue, correct? If that's the case, then yes...you'll need to replace it with a Class A chimney. You can run single wall up to the ceiling box though if you want. Double wall is recommended but I don't believe required. You might want to be careful about how much of the barrel you enclose... If you follow NFPA clearances for an unrated wood stove you'll be fine. With a properly built heat shield IIRC that gets you around 12" for the barrel going on memory here)
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| [+] rocket mass heaters » Have fins been added to top barrels before? (Go to) | Scott Clark | |
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Here's what the (running) mockup of my system looked like in the driveway...
And the final install in the garage: 
The system runs like a champ, but there's still a tiny bit of room for improvement...the final exhaust pipe is still probably a little hotter than it needs to be. I can put my hand on it and not get burned, but I don't want to keep it there for more than an instant. Never seem to get any smoke at all...there's a little steam as the system heats up, but that's it. The weird looking horizontal pipe is going to have a blower hooked up to it shortly to make a "heat scavenger" for lack of a better term. The water heater still has the original flue pipe in it (it was gas fired) and the swirly heat exchanger inside. Originally hot flue gas heater the water, but I'm going to make it run in reverse--force room air down the heat exchanger so the hot bell will heat the air...then it will exit the bottom of the bell at the old burner location and go out into the room... I'm hoping to get my EGT down...on the (small) chance that I'm able to scavenge enough heat to cause a draft stall, I can put a speed control on the blower. Given that it probably won't get over freezing until next year, it's probably not going to be an issue no matter how much I cool the bell off... Makes for kind of a funny looking machine though. It's a nice aesthetic if you like your place to look like you have part of a steam locomotive in it lol. It's in the garage, so whatever. I actually kind of like the industrial look out there. |
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| [+] rocket mass heaters » Have fins been added to top barrels before? (Go to) | Scott Clark | |
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One of these days I'd like to find an extra lid for my barrel to experiment with... I know of at least one type of heater that uses little pins in the convection air stream as part of the heat exchanger...I keep wondering how much more heat the top of the barrel could radiate with a whole bunch of long (say 3") nails welded to it... Would give it a ton more surface area to radiate off...well, as long as you don't mind it looking like a porcupine lol. Even a few big ones (like pieces of rebar) would help I would think. My system doesn't have a mass (just a single bell), so I'm looking to radiate as much as possible...in a traditional system you' don't want to strip off so much there's not enough to heat the mass...
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| [+] rocket mass heaters » Lincoln 60 fire clay? (Go to) | thomas rubino | |
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I've recently had about 150 pounds of Lincoln 60 go through my hands in recent weeks... My own experience (after a lot of experimentation) was that straight clay pretty much always cracks, regardless of how much water you mix with it. Dry cracks less. Starting with a 5-2 mix of clay/sand I had to work my way up to a 5-7 clay/sand mix before it would dry without cracking. At that point it's more sand than clay (and what I ended up using for mortar). I did notice that it's far less prone to cracking if you dry it quickly...like with a torch. Mine had to air dry inside where it wasn't all that warm..maybe using an IR lamp or leaving it out in the sun on a hot day might help. I don't know...everyone says it's crack resistant, but I was having a hard time with it. Makes a pretty good binder though, and my kids have had fun playing with the extra I have.
Interestingly, the clay I dug out of the yard seems to have a lot of sand already in it, and will air dry crack free every time...though it's not all that plastic. |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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I still don't know what you guys are talking about, but I'm kind of a visual learner...maybe a diagram would help lol.
Haven't posted in a while...been very busy. The Dragon is now officially in the garage and has been run twice for about 3 hours each time. Got it basically wrapped up on Sunday...this morning we had our first real snow in the valley. Just in time! I scored a bunch of free wood a while back...a guy about 20 miles north of here had a bunch of broken pallets and construction cast offs...here's some of it at the back of my yard. 
Pile on the left is how I got it...then I was cutting it to length with the chainsaw (middle pile) and then splitting it with an ax (right pile). I got quite a bit of it cut and split, but I've got a lot more to go. Also called around and found a local building supply store that pretty much always has pallets to give away...I can just go down there whenever and load up the truck. I have a bunch stacked up at the back of the yard right now...not really sure when I'll have time to break them down though. I decided pretty early on to just cut the chunks with the nails off and put them aside...I think I'll just make charcoal out of them later, rather than spend a ton of time pulling nails. They can ether be turned into charcoal, or be burned to make it. Either way, no waste I guess. And here she is, up and running in the corner of the garage... 
It's sitting on a base I made for it...bottom layer are these big clay building bricks (with air gaps on all sides of the bricks), then a 1/2" layer of cement board, then 2 1/2" of refractory/insulation, then a layer of basically clay mortar on top to level it. Then the core is built on that. After 3 hours of running, I stuck my arm under the base to see how hot it was...the cement board was warm, but not hot directly under the core. On either side of the core it wasn't even warm, so the heat appears to only penetrate directly under the fire, and doesn't spread. The insulation must be at least reasonably good I think. The bricks were mortared together with masonry sand and fire clay. It's not going to win any beauty contests, but it works. I tried to to keep the joints as thin as possible. The brick work was kind of fun, if time consuming...kind of like frosting a bunch of little cakes. Had to cut 4 bricks to make it all go together (had 4 6" gaps in the ends). A masonry disk in the angle grinder made quick work of it though. The only bricks not mortared in are the ones around the top of the feed tube...I left them loose so I could fine tune it. Runs great though...garage was 50* when I started...after a couple of hours this is what I got: 
It was almost too hot lol. I opened the door to the rest of the house to start warming it up...and it actually did make a noticeable difference in the rest of the house. I have the day off tomorrow, so I may try and cast my heat riser (still running on the old piece of chimney). First thoughts--it's a very powerful heater! It's only a 6"...not sure I'd want anything bigger in my place. My garage isn't insulated very well at all, and it practically ran me out of the place. I put a big fan up that blows air at the heat shield, so it wraps around the back of the barrel and bell and blows out the other side...seems to help even out the temps in the room enormously. Barrel and bell both get plenty hot. Got a tea kettle to (barely) boil on top of the barrel. The exit pipe gets hot enough you don't want to keep your hand on it, but you can touch it and not get burned. Draft was nice and strong. I have about 12' of vertical pipe...the last 4' are a triple wall Class A chimney with a stainless rain cap. I was kind of surprised at how loud it was...I could hear the snap-crackle-pop all the way upstairs on the other end of the house lol. I do have a question for you guys that run these all the time--the coals seemed to build up to the point I didn't want to put any more wood in it after about 3 hours...is this normal? The charcoal wasn't being consumed fast enough to just keep putting wood in all the time. After I quit adding new wood, they burned down to mostly ash, but it took a while... Also was wondering what a "normal" burn time is for one of these...3 hours seems about right? I filled a 5 gallon bucket with sticks, and burned through that and little more in that time. What's next? Finish cast heat riser, put permanent legs on the bell (I welded adjustable feet on it so I could level it while installing it). Going to make legs out of some big pieces of rebar, but I have to fill up the tanks for my torch first...going to bend them outward to give it a bigger foot print. I'm thinking about putting a coat of perlite mud all over the core, though it seems run fine without it. Core was still slightly warm this morning. Anyway, I'm sold on it. Thinking about building a system for the rest of the house, but it would be a next summer project. The place it would have to go doesn't have a ton of room, but would be pretty well suited to building a bench mass instead of just radiant bells. The idea of heating the majority of my house on free wood has a lot of appeal to me. |
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| [+] rocket mass heaters » Heat riser- square or round? (Go to) | Robert Hohulin | |
I was really happy to find a source locally...there's a big cement plant just north of town that sells Lincoln 60 for $7 a bag (!). Found them after calling all the usual building supply stores...most of them had no idea what I was talking about. And when I went shopping for Perlite, I ran into the same sort of thing...the people at Home Depot and Lowes didn't even know what I was talking about...the people there were just about useless. No offense to anyone of the people there...there's just soooo much stuff there, nobody seems to know what they have (or don't have). Local hardware store had the big 4 cu ft bags in the back for $20. Go figure. And for a heat riser, you might want to research how to make a cast one...you could always use that piece of metal for the inner form. |
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| [+] rocket mass heaters » Insulated base for combustion unit help! (Go to) | Glenn Herbert | |
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So, I'm kind of in the same boat right now... I'm building an insulated base for my core going into the garage...the bottom layer is going to be a piece of delta rib steel roofing (ribs down). With only the ribs touching the concrete, there's a minimal contact patch and 6" wide air gaps that will run the length of it, so there's pretty much no way for the concrete to get hot....
My issue is what to put on top of that. I want to use some sort of perlite insulation, but it has to be structurally pretty strong since it has to support the weight of the entire core/barrel assembly. I have plenty of fire clay on hand, as well as sand and perlite. Right now I'm leaning toward the recipe for castable refractory at backyardcasting.com...only thing is it does contain some Portland cement (as well as fire clay, perlite, and sand). With the bricks of the core between the fire and this base, I'm not sure if it would get hot enough to matter...but I only plan on building this thing once. I'm concerned that just using a fireclay/perlite mix won't be strong enough to hold the weight. I'm planning on making the base about 2.5" thick. I'm making sheet metal sides to weld to the bottom steel that will make the "form" that holds it all together. Hopefully that will make the "box" strong enough to also give some support to the goop. If I need to, I can weld in cross braces...which might help act as a sort of rebar for the goop in it. One more issue--the weather is turning, and it's probably not going to get above 50* F from here on out...and I need this thing to dry as quickly as possible so I can assemble the core on it. If I just use a clay mix, I'm worried it'll take forever to dry. It would dry out quickly with the core running on it, but I can't assemble the core until it's dry...sort a chicken and egg sort of situation. Any thoughts or suggestions would be greatly appreciated! |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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That's a lot of numbers...and even after reading it several times, I'm still not sure exactly what you guys are talking about lol. Are you calculating the transition area from the barrel to the rest of the system in a traditional RMH?
One other variable in my system that I haven't been able to test yet is the heat riser...for these tests I've just been using that old piece of chimney. It works, but it's also about 4" shorter than the one that's going to be permanently installed in the stove. I'm only missing one of the ingredients for the cast riser I'm making, so when that arrives I'll be able to finish that too. It'll be the standard height of 2" from the top of the barrel (around 33" if my memory is correct), with 3" of insulation around the 6" inner pipe. OD of the heat riser will be 12". I have to believe that the improved heat riser will improve draft by a good bit... The top of the barrel gets pretty darn hot now...it'll get smokin' hot when it's done. Speaking of, has anyone here done anything to make the barrel top a better heat exchanger? I had the thought that anything that increases the surface area would allow it to dissipate heat faster, and cool the top down...perhaps improving performance? I know of at least one type of heater that uses an array of little pins in the heat exchanger...air is blown over the pins in that design. Anyone ever hear of something like that on a rocket stove? Just thinking out loud here... Even a few big "pins" would help, though it would look kind of weird. Some bits of rebar cut to say 2 or 3" long welded on would work. Or, if you don't mind it looking like a porcupine, you could pound a whole bunch drywall nails (or any nails with big heads) through the lid (pointy side up). Hmm. If I could score an extra lid, I could do some experiments...if it doesn't work, I could just put the plain one back on... Anyway, like I said...just thinking out loud here... |
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| [+] rocket mass heaters » Clay for finishing off a Rocket Stove mass bench..? (Go to) | Lemuria Love | |
Interesting... The area we're in was somewhere near the east coast of Laramidia, though exactly how close I'm not sure. It's kind of funny, but spending so much time digging for my drain system sparked my interest in local geology. I was really starting to feel like I was one with the ground lol. I had several rocks that were too big to get out in one piece, so I broke them open with a sledge hammer. Kind of fun seeing the bright clean granite inside...got me thinking about how that's the first time in 70 million years that anyone has seen it... The clay layer that I hit seemed to have a lot of sand, but it does hold its shape. We mixed some up with water and put it in a red solo cup, and smooshed the sides up to hollow out the middle. After drying for a few days I popped them out--had a fairly tough clay cup . The kids thought playing with the stuff was great fun... I would think with as much sand as it has in it, I could pretty much use it straight up as cob/adobe after adding some sort of fiber binder.
I'm curious what's under the clay layer, but I'm not sure if/when I'll be able to dig a hole deep enough to find out lol. A quick internet search for Lemuria didn't turn up much, but searches involving "clay" and "Scotland" seem to turn up nothing but clay pigeons...wouldn't have guessed clay targets were as popular as that in the UK. |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
Hi Peter, Yep...while I've been experimenting, I've just been dry stacking the bricks. It's been nice since I can just re-arrange them like a bunch of legos to try different things. I have a bunch of Lincoln 60 in the garage, so I can mix some up to seal them during the final install. And yes, it's a 6" system. The outlet of the bell is actually about as low as I could get it...there's a chamber at the bottom of the water heater that used used to house the burner assembly/air inlet so the actual water tank sits up pretty far from the ground... There's probably 2 or 3" between the pipe and the actual bottom of the tank... |
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| [+] rocket mass heaters » Clay for finishing off a Rocket Stove mass bench..? (Go to) | Lemuria Love | |
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Same sort of situation here...my house sits square on top of the Idaho Batholith...one of the largest single granite formations in the world. My yard is full of the stuff. I recently had to dig a fairly deep trench as part of a drainage system I was putting in, and learned something new...the granite all over the yard appears to be surface deposits from the last ice age...the valley where I live was filled with a glacier that dropped these big stones all over the place about 12000 years ago. When you start digging, it seems like rocks mixed with a little dirt. At about 3-4 feet, you hit a layer of clay. It's very sandy clay, but clay nonetheless... If you dig down far enough, sooner or later you're going to hit the solid bedrock of the batholith itself, but I have no idea how far that is. I'm close enough to the base of the mountain, it's probably not very far.
Anyway, I don't know anything about your local geology, but you never know...if you do some research you might find there's clay closer than you think... |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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Got a lot done this weekend...still having unseasonably warm weather this year, which I'm lovin`
. Finally...after a lot of sweat, cutting, and welding, I have a full mockup of the rocket stove sitting in my driveway. Here she is...
Excuse the mess in the driveway lol. Here it is, bell and all ready to run.
The outlet for the bell is welded on, then the 45 just slips onto it. I welded up a bracket that the pipe is strapped to with a big worm clamp, which gives it a lot of stability. Seriously, it's not going anywhere lol. The bracket is made from angle recovered from an old bed frame. The outlet of the barrel is welded in place, but then just slips into the hole in the bell. You kind of have to wiggle the two of them together, and then make sure the barrel is centered over the hole in the core. I was able to cut the bell accurately enough so that when the whole thing is assembled it all fits together correctly. Small victory for me .
First time I tried to fire it up after moving the core over to the driveway didn't go so well...the thing just *would not* draft! Got a nice hot fire campfire burning straight up the fire box lol. Great. Lots of smoke...my kids were there (as they usually are)...they weren't impressed with dads creation. Eventually figured out that the firebox opening was way too big...scrunched it in, and it got going. By then it was dark, and I couldn't really see if it was smoking or not. Once it was good and hot, ir seemed to run ok. Yesterday I lit the second fire in it. Before that though, I cut down the pipe going from the stove to the bell so it's got a much shorter horizontal run between the two. Second fire went much better...got a draft going almost immediately, and then it took off. It smokes a little when it's cold, but once up to operating temperature it burns clean. Some observations: Barrel gets *very* hot, which is good. The bell is kind of interesting...while it's warming up, the top doesn't get very hot, but the sides do. It would appear that the flue gasses aren't rising all the to the top before being sucked out the exhaust... When the stove is really going, it appears to work as you'd expect, with the top getting nice and hot (though still not as hot as the sides). Also, the vertical flue pipe doesn't get very hot...it's a thin single wall pipe, and I can keep my hand on it even when the stove is up to temp. To me, that's a sign that it's just about as efficient as it's going to get... I bought a piece of 4" pipe that I can weld a flange to so I can hook up a blower, and blow air down the heat exchanger of the water heater...which would extract even more heat from the system. I think I'm going to experiment with this (and a variable speed fan), but I have a feeling that my exhaust temps are low enough already that if they get much lower I might have an issue maintaining a draft... Anyway, it looks like the system works as it should. Next step is just going to be moving the whole thing into the garage and poking the pipe out the roof. Then I just need to start scrounging for wood! |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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The stars aligned to give me a day off, extremely nice weather for October, and kids in school...so I got a bunch of stuff done
 . First, got the paint ground off one of my barrels...a 40 grit sanding disk will cut through just about any coating like a light sabre lol. Here it is all shiny and new looking.
I picked up a piece of ventilation pipe that was originally a fire stop...it has a big butterfly valve contraption inside to snaps shut if a fire ever gets into it. Ironically, it's going to have a lot of fire (or least fire exhaust) in it... I got it because it's a 6" piece, and very thick metal...like 14 gauge. Much thicker than a standard stove pipe. I took all the mechanics out of it, sanded all the zinc off it, and welded up all the rivet holes, etc. Been a while since I've really done a lot of welding, and it showed lol. My puddle control got progressively better as the afternoon wore on. Here it is fitted to the hole I cut in the barrel. 
And here it is fully welded into place. 
Obviously you want to position the bell as close to the barrel as possible, so I'm probably going to chop the end of it off to make it a shorter run between the two. Also probably going to use that as the outlet of the bell and stick a 90 on it to go up and out of the house. Speaking of the bell, I got all the insulation off the water tank. It was...messy lol. But, it's basically ready for plugging the holes and installing the inlet/outlet and painting. 
Having the barrel ready, I decided to do a mockup of the whole thing, sans bell since it's not ready yet. I built a 6" core from my fire bricks. I cut a 6" diameter hole in the bottom of the barrel, and dropped my piece of Class A chimney in it for a heat riser. I'm making a cast riser, but don't have everything I need yet, so this works for a test. The barrel has a removable lid, so I just dropped it in and put the lid on. I added a couple of large chunks of granite for weight, to keep the barrel stable. We had a big wind storm last night and it's still standing, so I guess it worked... Anyway, here's how the mockup looked: 
Took a while to really get it going...we had a lot of rain last weekend, and all the wood on the property was slightly damp. Ended up splitting an old 2x4 into sticks to get a really hot fire going. Drafted very well! Here's the fire... 
It was (not surprisingly) smoking on startup, but it cleaned up with the decent wood. Honestly, it ran great...my only concern is that the exhaust wasn't very hot. At the top of the stack, even on the "good" wood, I probably wasn't going to burn myself with the exhaust. It was not, but not what I was expecting. The barrel got cozy warm, but again...not as hot as I was expecting. I think this is probably the result of: Wood not dry enough Heat loss through burn tunnel Feed chamber and burn tunnel slightly too small. It ran great without any mortar in the joints, but maybe sealing the tiny gaps would help... Once thing I love about using loos bricks, is they're just like legos...I can try different configurations until I'm happy I'm going to make the bottom end slightly bigger and see if that helps. It should only have an increased draft once it's hooked up the house and the stack through the roof... Anyway, right now it's a working model, and seems to work like it should. It's got me thinking about the possibility of putting a true RMH in the house...I could replace the ground level pellet stove with an 8" system. The pellet stove is vented into a clay lined brick chimney...it's probably 25' (+) to the top of it. Once it had a draft going, I'm sure it would really run... The mass could be a roughly L shape around one side of the room. Only thing is the room isn't all that big, and it would reduce the floor space. OTOH, it could probably heat the entire 1st floor... Anyway, making progress. I just need to save up my pennies for the rest of the stove pipe to build the vent, and get the rest of the stuff to build the cast riser. I'm going to use the fireclay dusted perlite/sodium silicate/furnace cement mix. |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
It's funny...that thought didn't even occur to me until I read another thread mentioning a "rock and cob lasagna"...but it's true. My little stone forge will stay hot for hours . Here it was under construction...
There's a stone slab on the bottom that's hard to see. Here it is finished-- 
I put stone on five sides in an effort to make it more efficient, at the expense of not being able to work really big pieces of metal. But it works great...here's a piece of steel at somewhere around 2000*. 
I accidentally melted a couple things by leaving them in the fire too long...steel melts at around 3000* I think, so the fire is plenty hot in there. 5 hours after a burn, that stone on top is still plenty warm. Here's the kind of rocks I have all over my yard...these were pulled up while building my drain system next to the garage: 
That's a 4" drain pipe in the background, to give you an idea of how big they are. There's a bunch in the back yard too big for me to move...probably a couple hundred pounds. Would make a lovely mass in a bench .
And with my drain basically done, I'm starting to work on the rocket heater. I got a 55 gallon drum for $10. Need to strip the paint off, and cut one end open. Also tore into my water heater...got the gas valve/burner assembly out, so I can hopefully sell it. Now, there was some fiberglass insulation hanging out of the burner access hole, so I assumed that these probably just had a layer of fiberglass under the out jacket. WRONG. When they build these they put the outer jacket over the tank, and inject expanding foam into the gap! Arrrg! I cut open the outer shell with a sawzall along the seam, and "peeled" the jacket off. I was hoping to reuse it (possibly as a form for the heat riser), but it got kinked a bit because it stuck to the foam really bad. 
The stuff on the sides came off in mostly big chunks...the stuff on top is really stuck, and is going to make a real mess to get off  . If they're all like this, I'm probably not going to deconstruct another water heater any time soon...it would be easier and faster to weld a couple of barrels together to make bell.
Anyway, making progress...it was downright HOT this weekend (well, for October lol). Hoping the weather holds out long enough to get this thing together... |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
You're correct of course...I don't get enough sleep these days for things like simple geometry...lol. There are a couple of lube joints in town, I'll see if they have anything. Also think I found a source for the big drums, with removable (clamp style) lids for not too much. And last night I took some of the bricks I got for free, and built a quick mockup of a rocket core to show my kids what it would look like. It's like a 10 minute build...bricks stacked on dirt. We burned some yard debris in it (bits of wood, pine needles, couple of pine cones, etc.). The thing is full gaps all over, but surprisingly it ran just how it was supposed to...once it got going the "heat riser" drafted well enough that you could see the fire burning sideways down the burn tunnel. You could actually watch the fire through the gaps in the bricks lol. The fire was a little lazy, but given how leaky it was I thought it ran pretty good. Didn't have my phone handy so I didn't get a pic until after I put the fire out. 
The boys love anything involving fire of course, but if nothing else I thought it was an interesting proof-of-concept. Looking forward to building the real thing out of actual fire bricks... Also had another thought--if I ever do build a true RMH, I've got TONS of stone I could use for mass...I'm living right on top of the Idaho Batholith, and my yard is basically a bunch of granite with some dirt on top. I've got all the rocks I could ever use (and then some). It's a 70 million year old formation, with some really big (12000 year old) glacial deposits. They're all kinds of weird shapes though, which makes them difficult to build with. I've already used them to build two fire pits and a forge out back. Would love to have another way to actually use them, rather than just tripping on them in my back yard. |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
Brilliant...how did I miss that searching I wonder? |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
I guess longevity isn't as big of an issue anyway, since it would be a (relatively) easily replaceable part...and I like the idea that it's round and smooth. I could get some steel ducting for next to nothing...if I scaled it down to a 6" system, I'm guessing a 10" outer tube is probably preferable to an 8" one, since that would only give 2" of material between the two... |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
Thanks for the input Allen! The heat shield is built to NFPA specs for an unrated stove...I forget the exact dimensions (it was the first thing I put in quite a while back). Stove gets around a foot of clearance IIRC. I came across Dragon Heaters when I was surfing for ideas...they look pretty nice for sure. So, as of this weekend, here's where I'm at-- Picked up a load of fire bricks from a couple in Florence that were moving...got 66 of the big ones (didn't weigh one yet, but they're fairly light) and 9 half bricks (not half as in the skinny ones, but half like big ones cut in two). They also threw in some regular old red bricks and these weird things that are about a foot tall, 4" thick, and have to holes down the middle (picture a cinder block that's tall, skinny, and made out of clay). No idea what their original purpose was...but they were free, so what the heck. Got the whole pile for $70, which seems like a pretty good deal. Also picked up an old water heater for next to nothing. It's a 2006 unit, and in decent shape. So, right now my plan is to use the fire bricks to make a burn tunnel...debating on using them for the heat riser, or making one of the castable ones. Anyone want to convince me which is better ? I would think 66 bricks would be enough to make the whole thing if I wanted to, but without making a mockup I don't really know. Maybe someone with more experience can chime in. I think I'm going to make the rest of it from a 55 gallon drum. Depending on how tall I need to make the heat riser, I could always cut off a section of another barrel and weld it on top to make it taller (if need be). Then make the water tank into a bell, and vent that up to the roof with black pipe. Sound like a good plan? |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
Looks like a nice solution...any ideas on longevity compared to fire brick? |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
Thanks for the input Thomas! And yea, after thinking about it last night, that vent would be too small to work. Also did some reading on bells, and they sound like they might be the ticket. Revisiting the water heater tank, I had the thought of just making it into a bell, and putting a blower on the vent pipe to blow air down through it. The heat exchanger would work exactly in reverse of heating water...the water jacket would be filled with stove exhaust heating the pipe, and the blower would vent warm air out the bottom of the tank into the room... All that would really be required would be to weld an inlet and outlet onto the tank. On option D, the wood going through pyrolysis pumps a bunch of wood gas into the fire that gets burned...it's still a net heat loss into the process, but I think that makes it less so. His stove appeared to be burning very hot (and really flared up until the wood gas ran out), I don't think it would produce any smoke. It would mean less heat output (at least until pyrolysis is complete), though how much I have no idea. It would be easy to put a charcoal kiln in the backyard...would be nice to harness the excess energy instead of just venting it to the atmosphere, but if that's just how it is...it's how it is lol. Here's what I have in there now: 
That's a 7" piece of class A chimney that I was thinking about using as a heat riser...and yes, I know that metal will eventually die a slow death .
The stove is a heavy little thing...approx. 1/4" thick steel. 
To convert it, the bottom would need to be filled with some sort of refractory material, then build a firebox in that door hole. The vent on top could be cut out, the hole enlarged, and a heat riser inserted. Add a metal barrel on top, and you've got a rocket stove. I can't see any reason it wouldn't work, but I still think it would take more "creativity" than just starting from scratch. And I did find a couple people selling used fire bricks...a guy in Arlee and one in Florence. They both look like they came out of a kiln...they're the big thick ones. I have to go to Missoula on Friday to pick up stuff to build a French drain next to the garage (had flooding last spring), so I may check them out. And I'm originally from Butte, so I know a thing or two about Montana winters . Been in Hamilton since '05, and last winter was by far the worst I've seen since we moved here..really hoping this winter isn't as bad.
This was my car in the driveway...I had to shovel the whole thing by hand everyday. By spring I was...ready to be done shoveling lol. 
Anyway, thanks again for the input! |
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| [+] rocket mass heaters » Couple of quick Noob questions on design... (Go to) | Scott Clark | |
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Hey guys,
I'm new to the form, but I've spent...lets just say a *lot* of time reading here lol. I stumbled across RMHs a while back, and the concept hooked me. I was already in the middle of installing a wood stove in my garage, but stopped to give this whole this whole thing some thought. About 10 years ago I was an HVAC type service tech (actually worked mostly on gas fireplaces, pellet stoves, and traditional type wood stoves), so I'm already pretty familiar with how to make things hot lol. I'm currently running 3 pellet stoves and a forced air propane furnace in the house. I have an old Quad 1000 I could easily repair and install in the garage, but I'm already spending more than I want on pellets for the rest of the house...thus wanting to heat the garage with wood. I can collect deadfall off my 5 acres, and would also like to scrounge old scrap to burn. Again, trying not spend a lot of money on energy if I can afford it. I'm also building a small dual screen solar panel to put on the front (south facing) side of the house. With winter approaching I'm afraid I may run out of time before it's done though...I have a *lot* of projects to finish before winter. I live in the Bitterroot Valley...if there's anyone else here from Montana, you remember what last winter was like lol. As a side note, I have decent fabricating skills...somewhere above handyman, but not a pro by any means. I've been tinkering and building engines and things for 20 years. I have a Hobart MIG setup, a cutting torch, drill press, etc. No real machine tools though. Anyway, on to the rocket stove... My garage is very small due to be a weird add on to the house, so I'm trying not to take up too much room with the heater. The wood stove I was installing was made from some sort of old pressure tank...very heavy steel, a little smaller than a 55 gal. drum I think. Sort of a really heavy duty barrel stove. And it's set up vertically (6" outlet). I built a heat shield to specs for an unrated stove so I could put it in the corner. I was going to run black pipe to the roof, then the standard Class A chimney/roof support/flashing/cap. Total length of the vent was going to be around 14'. Then I started thinking about an RMH...honestly, I don't have enough room for a big mass, but I did have a couple of thoughts after doing a lot of research...would love some input on these ideas... A) Build an RMH out of a 55 gallon drum, sans the mass (RH?) and vent it like I was going to vent the other wood stove. Simply connect the outlet of the stove to the vertical pipe (bet once it was hot it would draft like a hurricane lol). More efficient than the old wood stove, but still going to loose a lot of heat up the pipe. Probably the cheapest, simplest way to go. B) Build a Rocket Stove as above, but instead of just venting it straight through the roof, port the exhaust into an old gas fired water heater...the outlet of the barrel would simply be connected to the flue inside the tank. Straight in, then a 90 up. Then, vent it normally out the top and up through the roof. I can weld a steam vent to the top of it for safety if necessary. When filled with water, it would give a large mass for the exhaust to heat, and hopefully retain. Being vertical, it would have a minimal footprint. Only real issue I can think of is the vent inside the tank is probably only 3 or 4", which might lead to drafting issues... This might be mitigated somewhat by having a fairly tall vertical pipe above it, and the fact that it's all a vertical run after the outlet from the barrel... I did a ton of searching, and couldn't find an example of anyone trying this... C) Try and retrofit the old barrel stove into a rocket heater. It's already vertical, and theoretically I could cut the outlet off the tank and insert a heat riser pipe into it. Would then need to put a barrel on top of it (a 30 gallon would probably work). The door is square, and could have a burn chamber built into it. Getting insulation inside would be...interesting. Not a lot of room to work in there, and the top is welded. As thick as it is, I'm not really interested in cutting into it. I'll take a picture of it and post it to see what you guys think... The advantage here is I could re-purpose the old stove, and maybe save a few bucks doing it. Would take more creative engineering than just building one from scratch inside an old drum though. It weighs a couple hundred pounds, so once it was hot I'm sure it would retain some heat (well, better than an oil drum anyway...) (Edit) D). Also found a video of a guy who incorporated a charcoal retort into a 55 gallon rocket barrel stove...it's a 5 gallon metal can situated right above the heat riser, and below the lid of the barrel. There's a vent hole in the can (facing down) that vents the wood gas into the heat riser. Love the idea of this, since the kids and I built a pit forge in the back yard. Would love to have "free" charcoal to pound metal with...anyone else ever hear of this? Anyway, all of these things exist more or less as nothing more than drawings on the back of an envelope (well, except for the old stove). I'll take some pics tonight of the old stove and the space it's in and see what you guys think... Thoughts and/or suggestions are appreciated... Thanks! Scott |
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