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I finally finished my first rocket mass heater!  RSS feed

 
dave marth
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It's done. Just not aesthetically pleasing yet. I will get pictures up tonight if possible.

I have run it several times and believe is now finally all sealed good enough. I have a brick bell over the heat riser and then it exhausts into a steel 55 gallon drum bell. Then out to the chimney. Works well so far but temp in PA are still a little t mild to really see how it performs.

So far it burns like it should with very little smoke.

Pics soon to come.

Thanks for everyone's help with my million questions.
 
dave marth
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Early build
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dave marth
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Some more
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dave marth
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And more. I have sand packed around the base of the bell as the floor and seems to be good I suppose.
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Satamax Antone
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I'm keen!

But it's not finished!
 
dave marth
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What do you mean your keen? And I'm just gonna maybe do a clay slip on the outside and that's it. Maybe stick some rocket on the outside for a little more mass. Don't know yet. Any suggestions for the outide?


Also I want to make a glass front for the feed tube. Would an oven door glass for a regular electric cooking oven be high temp enough? I was thinking of looking in trash for a scrap oven and steal the glass from it.
 
Satamax Antone
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dave marth wrote:What do you mean your keen? And I'm just gonna maybe do a clay slip on the outside and that's it. Maybe stick some rocket on the outside for a little more mass. Don't know yet. Any suggestions for the outide?


Also I want to make a glass front for the feed tube. Would an oven door glass for a regular electric cooking oven be high temp enough? I was thinking of looking in trash for a scrap oven and steal the glass from it.


What does it mean in your language "to be keen on" something ?

What do you mean stick some rocket?

Clay slip is good, i think.

For the glass front, you need better than an oven door. May be pyrex would stand the abuse. Vortex at donkey's, used a pyrex tray, to make a a porthole in a stove door.

May be finding a flat enough and square tray would do for you.

Or you buy some neoceram.
 
Glenn Herbert
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"To be keen on something" does mean to be very interested and enthusiastic, though we don't tend to use the word "keen" bare, and it is somewhat archaic - it was common slang in the 1940s-50s era.
 
Dan Dronberger
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Looks good.

A question?

How much insulation is under it?

I for see a bad odor when the heat hits the tile/tarp and it will.

I was surprised how hot my test core got underneath. It burned the pallet it was sitting on.

Wish you the best.
 
dave marth
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So the heating season is coming to an end and I actually stopped running the heater for the most part. I have learned a ton with this first build. Recently I have filled my house with smoke twice and that was enough for me to quit for now on this current stove. I think it smoked back because temps were a little warm outside, not real warm but just enough to cause draft problems. I didn't incorporate a cleanout in my stove pipe so for me to prime the stove pipe I have to take the barrel lid off and light a paper in the bottom of the barrel where the pipe exits. Its a huge pain in the butt so that's gonna need to be incorporated in the next build.

Second thing i learned is everyone who said basement is a bad idea for a rocket mass heater is absolutely CORRECT! I just needed to find out for myself. For the past winter I have been running up and down my basement stairs about 15 times a night to reload and shuffle shake down the burning wood. I expected a couple trips up and down the stairs but not that many.

Next is my upstairs was around 70-74 degrees every night, after burning for about 5-6 hours. This is the real reason that basement location is a bad idea. The entire basement needs to heat up before the heat travels upstairs. I had a wood stove before I build this stove and the heat came upstairs way faster, that's because the rocket mass heater needs to build its heat first then it can spread around the house. So needless to say, i tried to spend all my time in the basement for easy refilling and staying warm!

Next problem was my feed tube. I mortared the entire heater together with just fire clay alone. This stuff is very fragile. A few weeks into running the heater, I noticed sand was falling through cracks in the feed tube area between the firebricks meaning my clay mortar is cracking and failing. I have the entire jtube surrounded by perlite and then on top of the perlite is sand. That's the sand that's filling into my burn tunnel. This is my first time mortaring with fire clay and I didn't know it would be that fragile. Now I know.

Another problem I had to combat is the fire climbing out of the feed port. This could be caused by a couple things. I used thicker splits than I believe I should have been using, causing them to not crumble down to coal as fast as I would have liked. This left more time for the fire to climb up the sticks. Also, I think if my feed tube was a little smaller the faster air flow might have kept flames down a little better. My fix was to bend a piece of sheet metal into a square and basically raise my feed port about 10'' higher to be taller than my sticks I was burning. Then I placed another piece of sheet metal over the top of the square to allow about 25% of the surface area of air flow in. That way if the sticks did flame up then the fire was still surrounded by more feed tube.

And the blue tarp and tiles under the stove are no problem at all. Under the burn tunnel, I laid a piece of ceramic fiber blanket on top of some plain bricks and build on top of that. It seems like a VERY effective insulation keeping everything cool enough to not transfer heat where I didn't want it.

So now whats next? Build a new one upstairs in my living room. There currently is no stove pipe in my living room so I will have to install that this summer. I want to do a build similar to the dragon heater castle builds out of the clay flue tiles. I will ad a cleanout t so that I can pre heat the stove pipe much easier. If I build one in my upstairs, my living area will be toasty within 2 hours I assume. My basement would go from 59-60 to 70s within an hour and a half with my current heater.

Now hears my innovative thought. I want to make a cross between j-tube and batch stove. That's almost what I had once I raised my feed tube with the sheet metal.

Is it possible to make a regular j tube stove then make a little bell that goes over the feed tube like a can or something the right size for the feed tube, and add a couple air ports for the secondary combustion? Here's what I think will happen. The sticks in the feed tube will obviously climb the sticks but the air port will be at a point that is proportionate to the system, not at the top of the feed tube. This way the draft wont want to run backwards because the feed tube air flow will be low enough that it still drafts correctly. This way its almost like a batch j tube. The flames would be going on in the feed port and the gasses would get sucked into the burn tunnel where more air is mixed in for a clean burn.

Does anyone have any experience doing this mod to a regular j tube?

I hope my wording is clear enough to get the ideas across.

Thanks
Dave

 
thomas rubino
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Congrats on completing your first season with a rmh! Sounds like you learned a lot ! Everybody does after their first season! If I read your post correctly what you are wanting to do with a "bell" over the feed tube is not such good idea... Hot gasses will build up and there would be a fair chance of a fireball when you open it up to add wood. But I may have not understood what you were proposing. Having a cleanout is always a good idea , however after the first startup , IF you have a proper chimney.... priming should not be needed. My rmh has never needed priming even when still wet , however it did need "help" with a hand held fan at the mouth of the feed tube when the mass was still wet.
 
Erik Weaver
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I have only used clay and water for my mortar and I had no trouble at all. The trick is that it must be very thin. Start with the dry fire clay, add just enough water to make it like pudding, then wipe that onto the surfaces of the fire brick that will be against one another, and I moved or grinded them together, whatever the right word is, until I actually felt the surfaces of the two faces touching. It is that thin of a "mortar joint." No thicker than 3-mm (roughly 1/8") and from what I've read, 1-mm is very common, and actually rubbing the faces together is not uncommon (as I chose to do).

I too am surprised that your floor did not get too hot. I assume you had a temperature robe down there? I've measured well over 500 F under the floor of my 6" j-style quite often.

Your thoughts on the modified feed tube have been tried, and I do not recall anyone reporting they liked the results. One caution if you try it, flame-ups have been reported when you lift that lid; folks report that if excess smoke puffs up while there is a sufficient flame present, it may release a large tongue of flame, potentially into one's face.




 
dave marth
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I understand what your saying about the fireball potential. I have to think there must be a way to maybe close off the primary air inlet and maybe open a port on top of the feed tube bell to clear gasses out before opening and reloading.

But anyhow, if there was a bell on top of the feed tube and an air inlet a a lower point than the bell would this mess with the mechanics of how th e system burns? I can't see how it would as long as I stick with the proper air ratios.

Here is a video showing what I'm talking about with my sheet metal feed tube top.
rocket mass heater feed tube bell cover:


https://youtu.be/jx0sQmpGdD4
 
Peter van den Berg
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dave marth wrote:But anyhow, if there was a bell on top of the feed tube and an air inlet a a lower point than the bell would this mess with the mechanics of how th e system burns? I can't see how it would as long as I stick with the proper air ratios.

You said it, the detail where you're bound to get problems with is the lower air intake. In a j-tube system all the air need to come from above, nothing otherwise. I've tried this with my first build, a bare core in the garden and it's no good. The same goes for the larger feed, I've been wrestling with that one for a week before I gave up and changed it to the same csa as the tunnel and riser.
 
dave marth
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Well that's not what I wanted to hear, but I believe you. The reason I was staying away from a real batch box is because this summer when I was testing, I tried to make a batch box that was long enough to fit the entire length of my 30 inch wood inside. I could never get it to burn clean enough and assumed it was because my burn chamber was too deep. I never did investigate any further. I remember when I asked you about the depth of the box burn chamber you said that the length wasn't a big issue. Is that still accurate.

Thanks guys.
 
thomas rubino
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Dave ; I watched your youtube video and the thing I noticed, is seeing your fire alongside the bricks... if you can see thru to the fire then the air is going in that way instead of down the feed tube as its supposed too. Use your fireclay mud to seal those gaps every time they show up. Its common to "choke" the air inlet, usually with bricks to create a venturi effect ,increasing the airflow velocity, adding a "can" to extend your feed tube helps if you have tall wood that could burn out from the bottom and topple over into your room. The extension hurts by changing the airflow patterns into your feed tube. I found it easier to cut my wood shorter , and if I use a piece of wood that sticks up I don't leave the stove alone till it drops down to a safe level.
 
dave marth
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Yes the fire is visible through gaps in my feed area. I left these unsealed like that because then I am able to remove the couple of bricks and clean out the tunnel. I realize that if it was sealed the draft would pull the fire down better. And cutting my wood shorter would fix my fire climbing up problem but then I would also be increasing my load frequency. Thanks for your tips though. I appreciate it.

Maybe my solution is to make my riser a lot taller so that I can make my feed chamber about 30" deep. Then I still want to try to fit a cover on the top of the feed to let air in but no flames or smoke out of the top. I am visioning something like a square cap with a funnel shaped Cone going down onto the fire so that the air is blowing down through that focused hole and no smoke or fire can come up.

Anyone follow or is that too confusing?
 
Glenn Herbert
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I don't see why you don't go with a proven batch box design. You load the fire once and after it's burning right don't touch it until it's done an hour later. A batch box also puts more heat into the mass faster than a J-tube.
 
dave marth
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I tried the batch box one time and I made it to fit about 30" splits. It kept smoking out of the riser giving me the impression that it was too deep of a burn chamber to run.
 
Satamax Antone
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Dave, raise your heat riser in that case. You need to overcome the friction given by the increased lengh the air has to travel through the sticks. That did the trick for me, on a smokey batch.


Can't you buy yourself a circular or bandsaw, and cut your wood back to 15? A little work. But if it stops smoking!
 
Peter van den Berg
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The test regarding batch box length was done on a 6" system. The normal firebox length is about 15" if I remember correctly. The testbed was 50% longer which I would regard as a large margin. But you built it 100% longer, so perhaps you were stretching it too far. Perhaps it could be done, provided the whole of the system is accurate to the recommended values.

Frankly, I have my doubts.
 
shilo kinarty
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Another problem I had to combat is the fire climbing out of the feed port

it's probably not another problem.
it's the same problem - location too low.
 
Bacon Lee
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Hello everyone

I saw you did two things differents here:
First you don't have a cob bench but you use the 55 gallon barrel. How do you store heat in that barrel? do you have cob in that barrel around a duct?
Second I see that you don't use the barrel around the heat riser, but you used the brick instead of the barrel, right? May I ask why would you call it a brick bell? What other things you do that it becomes a bell?

Thanks
 
dave marth
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Yes. I left out the cob bench and instead put firebrick inside the barrel as mass. Not as effective as I would have liked. And for the bell I just called it a bell because that's what I though that was called.

Anyway I'm redesigning everything completely. I'm gonna make a new thread called wood stove converted to rocket stove. I'll ask all my new questions there.

Thanks everyone here for all your tips and help. Great community.

Dave

 
Satamax Antone
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Dave, just convert that blady J tube to a batch, reusing your old wood stove door for the batch door.


http://donkey32.proboards.com/thread/1361/converting-8-6-batch
 
Scott Robuck
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I was a little worried. your early build pic. shows up with the "I'm finally finished" lol
 
Erica Wisner
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Thanks for the update.  I LOVE reports after a full heating season, so much more useful than baby pictures without follow-up!

With the clay slip mortar: Yes, it should be very thin.
We usually support around the firebox by layers of other masonry that double- or triple-seals.  Perlite mixed with a very little wet clay so it doesn't move (maybe 2 gallons of liquidy clay-slip, like thick paint, for 2 cubic feet of perlite).
Then a good layer of cob about 4" thick, or a second layer of brick with tidy, airtight mortar. 
You need a little room around the firebox for thermal expansion (perlite mixed as above seems to provide this, though the bricks can shift slightly over years.  Or you could do a ceramic-fiber fire insulation blanket if you can get it).  But if it is too unsupported, handling the wood will loosen the bricks, and loose materials like perlite or sand can flow into small cracks and make them bigger. 

Bricks expand with heat. cracks move. bricks cool and shrink. more sand gets in.  Iterative self-destruction of firebox. 
Include expansion joints (room for firebox bricks to expand), and don't back firebox with loose fill unless it is big enough particle size to stay out of cracks.  The expansion joints create a 'floating' firebox that can move slightly, independent of the cooler masonry surrounding it.  You may only need a little bit of fiberglass gasket between the firebox bricks and the cooler masonry, but you will need something if you want it to stay airtight.  Which you definitely do.

I like this overall design, it is not a bad idea since you want the heat to go upward in the basement.
But since it reverses the placement of masonry (around the firebox) and bare metal (the later barrel), the fire performance may not be exactly comparable to the more common J-style with bare metal around the firebox.  I would like to find out more from people using this masonry bell around the heat riser, to see how close they come to the same fire function and output temperatures.  But until you seal up the cracks in the firebox, it's not exactly a fair test. 

In contemplating the batch box - remember that the door is a CRITICAL component of a batch box.  If it is not the right size, and particularly with the right air feeds, the batch box does not burn clean. 
A leaky batch box, or box whose door is working loose and leaking, would also not be expected to burn clean. 
Dirty burn and heat extraction = creosote = risk of chimney fires and really obnoxious cleaning bills.
A good door, and the metal hardware to support the door without shifting the masonry as it is used and abused, is not cheap and easy to add after building everything else.  It has to be planned, with appropriate provisions for thermal expansion (metal expands more than masonry at the same temperature but metal outside the firebox may be a lower temperature than the bricks..... it's worth looking at good oven door framing, or a successful masonry heater design that you can see construction pictures, to see how to hang these doors and how to incorporate expansion joints so the metal and masonry can have a long and happy marriage).

We have done a lot of J-style heaters because we can shut them down with a couple of bricks on top, which is a $4 solution instead of a $400 solution.  I aspire one day to be able to do nice tight metal doors without being intimidated, but for now, I consider it a non-trivial concern when choosing a heater style. 

However, it seems to be non-trivial for inspectors too - a nice pretty door instead of a couple of bricks can go a long way to convincing official types that it's a "proper" masonry heater.  All the clearance rules are written for vertical openings, not horizontal holes in the floor.  Sigh.

Please keep posting if you do another iteration!
 
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