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rocket mass heaters

Couple of quick Noob questions on design...

Posts: 39

Location: Western Montana

posted 10 years ago

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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

thomas rubino

rocket scientist

Posts: 6355

Location: latitude 47 N.W. montana zone 6A

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posted 10 years ago

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Scott; If you don't have enough room for a mass then look into using "bells" instead. They take up much less room, and weigh less. A search here at permies will give you a lot of different bell options to look at. (A) a rmh without the mass is a rocket stove. (B)Trying to use a 6-8" rmh with a 3-4" vent is not going to work. Your horizontal pipe in the mass can run back & forth and over top of itself if your floor space is limited, but your floor needs to be strong enough. (C) Use that barrel to make a charcoal retort in the backyard. (D) That charcoal your wanting to make is wood you could be burning and it may rob to much temp from your indoor rocket, making it burn smoky. By the way ,don't know how long you have lived here but... be prepared last winter was mild compared to what it can be. Locate some clay & sand now before freeze up and get it home. locate a source of fireclay & fire brick or old red brick, should be easy in missoula. Get a copy of ianto evans book rocket mass heaters & read it .Tell all your friends about rmh,s they really work !

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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thomas rubino wrote:Scott; If you don't have enough room for a mass then look into using "bells" instead. They take up much less room, and weigh less. A search here at permies will give you a lot of different bell options to look at. (A) a rmh without the mass is a rocket stove. (B)Trying to use a 6-8" rmh with a 3-4" vent is not going to work. Your horizontal pipe in the mass can run back & forth and over top of itself if your floor space is limited, but your floor needs to be strong enough. (C) Use that barrel to make a charcoal retort in the backyard. (D) That charcoal your wanting to make is wood you could be burning and it may rob to much temp from your indoor rocket, making it burn smoky. By the way ,don't know how long you have lived here but... be prepared last winter was mild compared to what it can be. Locate some clay & sand now before freeze up and get it home. locate a source of fireclay & fire brick or old red brick, should be easy in missoula. Get a copy of ianto evans book rocket mass heaters & read it .Tell all your friends about rmh,s they really work !

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!

thomas rubino

rocket scientist

Posts: 6355

Location: latitude 47 N.W. montana zone 6A

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posted 10 years ago

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Scott; look at matt walkers cast riser using fireclay & perlite with a 16 gal grease barrel and a piece of sonotube for an inner form. Its cheap / easy and will work oh so much better than metalbestos.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

allen lumley

pollinator

Posts: 4154

Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''

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posted 10 years ago

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Scott : You could try Contacting a few friends you used to work with ! There are A lot of 5'', and a few 6'' oil fired water heaters still out there! Also check out
Craigs' List .

While I would never attempt to build a system smaller -the 5'' is do-able! The fine people at Dragon Heaters Dragionheaters.com have a few 4'' RMHs
available for sale to that part of the general public that understands RMHs but lack skills, or Time or Space ! At least check them out !

Good luck with your future Dragon ! For the crafts! Big AL

Late note ; It is only probably the angle that the picture was taken at, but as such it might confuse another member, I like to have my reflector shield 4'' off
of the wall I am protecting, and the Gap at the bottom more like 6'' Y.M.M.V. A.L.

Success has a Thousand Fathers , Failure is an Orphan

LOOK AT THE " SIMILAR THREADS " BELOW !

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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thomas rubino wrote:Scott; look at matt walkers cast riser using fireclay & perlite with a 16 gal grease barrel and a piece of sonotube for an inner form. Its cheap / easy and will work oh so much better than metalbestos.

Looks like a nice solution...any ideas on longevity compared to fire brick?

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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allen lumley wrote: Scott : You could try Contacting a few friends you used to work with ! There are A lot of 5'', and a few 6'' oil fired water heaters still out there! Also check out
Craigs' List .

While I would never attempt to build a system smaller -the 5'' is do-able! The fine people at Dragon Heaters Dragionheaters.com have a few 4'' RMHs
available for sale to that part of the general public that understands RMHs but lack skills, or Time or Space ! At least check them out !

Good luck with your future Dragon ! For the crafts! Big AL

Late note ; It is only probably the angle that the picture was taken at, but as such it might confuse another member, I like to have my reflector shield 4'' off
of the wall I am protecting, and the Gap at the bottom more like 6'' Y.M.M.V. A.L.

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?

thomas rubino

rocket scientist

Posts: 6355

Location: latitude 47 N.W. montana zone 6A

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posted 10 years ago

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Compared to firebrick , I'm guessing not as long . Mine is in its second season and its good as new ,including a removal this summer. Heres the differences I see ,they can be gently lifted off and moved ,they are round instead of square. With an 8" you have a 3" insulated riser. Getting the exact gap to top of barrel is a piece of cake. Would I build a fire brick riser ,sure if i couldn't get the materials to cast one. Either one works longer than a metal one.

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Satamax Antone

gardener

Posts: 3471

Location: Southern alps, on the French side of the french /italian border 5000ft elevation

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posted 10 years ago

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Scott Clark wrote: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.

That little stove just calls for a retrofit!

http://donkey32.proboards.com/post/11503/thread

Just to give you an idea of what can be done!

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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thomas rubino wrote:Compared to firebrick , I'm guessing not as long . Mine is in its second season and its good as new ,including a removal this summer. Heres the differences I see ,they can be gently lifted off and moved ,they are round instead of square. With an 8" you have a 3" insulated riser. Getting the exact gap to top of barrel is a piece of cake. Would I build a fire brick riser ,sure if i couldn't get the materials to cast one. Either one works longer than a metal one.

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...

Scott Clark

Posts: 39

Location: Western Montana

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Satamax Antone wrote:

Scott Clark wrote: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.

That little stove just calls for a retrofit!

http://donkey32.proboards.com/post/11503/thread

Nice job! I keep looking at that stove and going back and forth about using it for this first project... On the one hand, if you built a firebox in it, and surrounded everything in there with some sort of insulation, you'd have a super hot burn tube and heat riser. Put a barrel on top, and you've got a rocket stove... The bottom of it would radiate almost no heat, making it a good setup for connecting to a large mass...which I don't have room for where this is going. I'm sure I'll find a way to resurrect it as something else, just not sure exactly what that is just yet lol.
Just to give you an idea of what can be done!

Satamax Antone

gardener

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Location: Southern alps, on the French side of the french /italian border 5000ft elevation

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https://permies.com/forums/posts/list/10653#100285

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

thomas rubino

rocket scientist

Posts: 6355

Location: latitude 47 N.W. montana zone 6A

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posted 10 years ago

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Scott; A 10" outer and a 6" inner only gives you 2" insulation , you would want a 12" outer tube to have at least 3" insulation . The 16 gal grease barrel is 14 "and would give you 4" insulation. most quick lube shops / mechanic shops / dealerships, have these and usually will give them for free, especially after you tell them what you want it for!

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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Satamax Antone wrote:https://permies.com/forums/posts/list/10653#100285

Brilliant...how did I miss that searching I wonder?

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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thomas rubino wrote:Scott; A 10" outer and a 6" inner only gives you 2" insulation , you would want a 12" outer tube to have at least 3" insulation . The 16 gal grease barrel is 14 "and would give you 4" insulation. most quick lube shops / mechanic shops / dealerships, have these and usually will give them for free, especially after you tell them what you want it for!

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.

thomas rubino

rocket scientist

Posts: 6355

Location: latitude 47 N.W. montana zone 6A

3209

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posted 10 years ago

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Scott; Your living on top of the perfect mass material. doesn't matter what shape, if you can lift it ,it will work in a mass! Cobb is hard work to make ! The more dense solid rock you have , the less cobb you make ! You just need to locate your clay & sand and your RMH is practically built ,lol

For all your Montana Masonry Heater parts (also known as) Rocket Mass heater parts.
Visit me at
dragontechrmh.com Once you go brick you will never go back!

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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thomas rubino wrote:Scott; Your living on top of the perfect mass material. doesn't matter what shape, if you can lift it ,it will work in a mass! Cobb is hard work to make ! The more dense solid rock you have , the less cobb you make ! You just need to locate your clay & sand and your RMH is practically built ,lol

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...

Scott Clark

Posts: 39

Location: Western Montana

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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.

Scott Clark

Posts: 39

Location: Western Montana

posted 10 years ago

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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!

Peter van den Berg

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Just a remark: Your bricks are stacked dry as far as I can see. So there are small leaks all over the thing, hampering it big time. When moving into the garage, make sure everything is sealed properly. Moreover, when you add insulation around the tunnel and the bottom of the feed this will kick the thing into high gear. Maybe you could replace the final exhaust out of the bell to a lower location? I would recommend about 3" above the bottom of the bell. It's a 6" system isn't it?

regards, Peter

Scott Clark

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Peter Berg wrote:Just a remark: Your bricks are stacked dry as far as I can see. So there are small leaks all over the thing, hampering it big time. When moving into the garage, make sure everything is sealed properly. Moreover, when you add insulation around the tunnel and the bottom of the feed this will kick the thing into high gear. Maybe you could replace the final exhaust out of the bell to a lower location? I would recommend about 3" above the bottom of the bell. It's a 6" system isn't it?

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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Another thing Peter hasn't said, watch your transition area. Between barrel and the first stub of flue before the bell.

The ring projection between pipe edge and heat riser insulation should give you at least 1.5 the CSA, Some say up to three times is good.

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

allen lumley

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'Max' : Sorry, I feel like I dosed off there for 6 months ! Big transitional area CSAs is clear, but is is the 1st time I picked up on the term Ring Projection,
a simple explanation and a picture or two for for the un-informed would probably help more than just me !For the Good of the Craft ! Big AL

Success has a Thousand Fathers , Failure is an Orphan

LOOK AT THE " SIMILAR THREADS " BELOW !

Satamax Antone

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allen lumley wrote:'Max' : Sorry, I feel like I dosed off there for 6 months ! Big transitional area CSAs is clear, but is is the 1st time I picked up on the term Ring Projection,
a simple explanation and a picture or two for for the un-informed would probably help more than just me !For the Good of the Craft ! Big AL

Ring projection, the projection of the tube's wall into the barrel gap.

I mean, the surface of the wall of the exhaust tube as if it was completely inserted in the barrel up to the heat riser, comprised between outer shell of the heat riser, and the barrel.

For example, you have a flue or exhaust tube of 6"

That's a perimeter of 6"x 3.1415926 or so that's 18.84 inches.

Multiplied by the gap let say 2" = 37.69²

Heat riser CSA of a 6 incher 28.27

28.27² x 1.5 =42.41² So a gap of 2 inches with a 6 inch exhaust tube isn't good enough.

42, 41/ 18.84= 2" 1/4 so the gap needs to be at least 2.1/4 to have a ring projection of 42,41 square inches necessary for good performance.

If you aim for 3 times the CSA,

You could reverse it this way

2 inch gap

28,27²x3 = 84.82² /2 = 42,41/3.1415926 = 13.49 inches in diameter for the "transition area"

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

allen lumley

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''Max'' : O. K., I follow the math with a slightly better understanding of what the numbers are coming from and at least the glimmer of an idea where to apply them.

At exit from the Top of the Heat Riser the gases should all equally flow through the area of the perimeter of that system Xs the calculated height go the Barrel Gap.

A 6''system has a perimeter of 18.84 '', to find the minimum area that the gases must be allowed to sweep through we multiply the 18.84'' Xs the calculated
minimum height of the Barrel Gap (Systems CSA 28.27 Xs 1.5 = 42.41) this number is a measuring stick and should be the same size as the 18.84 perimeter Xs
the corrected minimum Barrel Gap, or our mathematical number 42.41 /18.84 ~ 2.25'' minimum Barrel Gap !

A 7''system has a perimeter of 22 inches, to find the minimum Area that the gases Need to sweep through we Multiply the 22'' times the Calculated minimum
height For the Barrel Gap ( Systems CSA 38.48 Xs 1.5 = 57.72) this number Functions as a measuring stick and should be the same size as the 22'' perimeter Xs
the corrected minimum Barrel Gap, or our mathematical number 57.72 / 22 ~ 2.62 '' minimum Barrel Gap !

A 8''system has a perimeter of 25.13 ", to find the minimum area that the gases must be allowed to sweep through we multiply the 25.13 Xs the calculated
minimum height of the Barrel Gap, (Systems CSA 50.26 Xs 1.5 = 75.40) this number isa measuring Stick and should be the same size as the 25.13 perimeter Xs
the corrected minimum Barrel Gap, or our mathematical number 75.40 / 25.13 ~ 3 '' minimum Barrel Gap !

In the last 4 lines you show the CSA of the 6'' system multiply Xs 3 and then divide by 2 Am I correct that This 2 is a minimum Heat Riser to inside wall of the
barrel Gap? Followed by dividing by pi to get the correct Transitional areas STARTING Perimeter !

Thats what makes sense to me, I want to make sure of finding the correct results, but its nice to know where the numbers come from so you can check your work!

For the good of the Craft ! Big AL

Success has a Thousand Fathers , Failure is an Orphan

LOOK AT THE " SIMILAR THREADS " BELOW !

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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allen lumley wrote:
At exit from the Top of the Heat Riser the gases should all equally flow through the area of the perimeter of that system Xs the calculated height go the Barrel Gap.

Allen, that's it, the theoretical surface of the projection of a perimeter into a gap, = ring projection to me.

And that has to be at the absolute minimum 1.5 times the CSA. Would it be on top of the riser or at the side of the barrel for the transition area. Up to 3times the csa for the transition area which seems to be the "safe" number. For the top of the riser, even several feet can be done no prob, so it's a minimum we're looking at, not maximum. That 3 times figure arose, i think because it was a convenient number for newbs.

At 4 times CSA, you get to the lower limit for bell's . Well, let me explain, a bell has to have a horizontal cross sectional area of at least 4 times the CSA to work at all. There's no upper limit, exept the ISA.

So again, that brings us back to that 3 times the CSA for that transition area, otherwise it might start acting as a bell if bigger.

A little side note; for example, heat riser's gap can't be smaller than that 1.5 times CSA, because of the laminar flow effect. The gases at the inside corner of the "elbow" where they exit the heat riser and turn; are completely stalling, and each layer goes a little faster as they're more distant form a surface. The top of the barrel stalls the gases too, due again to friction. The top of a heat riser can be made better, being rounded outwards, , like a rounded funnel. That means that the ring projection is bigger too. The absolute contrary of what everybody does

I suspect that the whole sheebang of a rocket could be tuned to a certain note, due to the hemoltz resonances. (at the top of the heat riser, enlarging it as i have described, would drop the note down)

Well, i'm going astray, due to previous life experience

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

allen lumley

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''Max'' It makes sense now, let me try it in the morning ! Big AL

Success has a Thousand Fathers , Failure is an Orphan

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allen lumley

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''Max'' : So- by knowing the Systems size we know the diameter, hence the Cross-Sectional Area CSA, and the perimeter, and can calculate the minimum
needed Ring Projection Anywhere a given sized pipe flows its gases into another one ! Even, or Especially the Transitional Area !

This takes us al the way back to The Good Book . Know your CSA, and keep it Whole-y! With More drag designed out of our systems, we should be better
able to deliver a predictable average exhaust gas temperature at the base of our final vertical chimney !

In English of course the flaring mouth of a trumpet is called its 'Bell', lets just say we are talking about a potentially perfect shape -a tapered flaring funnel
shape with sweeping curves !

Does this All make sense to you ?! For the Good of the Craft ! Big AL

Success has a Thousand Fathers , Failure is an Orphan

LOOK AT THE " SIMILAR THREADS " BELOW !

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Makes perfect sense.

God of procrastination https://www.youtube.com/watch?v=q1EoT9sedqY

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.

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...

I agree. Here's the link: https://woodheat.net