Newbie - Rocket Mass Heater Build

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Re: Newbie - Rocket Mass Heater Build

Postby Oddmar » Thu Jun 14, 2012 6:53 pm

Figured i'd better post an update...

Took some pictures but haven't pulled them off the digital camera yet...I made a feed/ burn tunnel like Matt did for his house, using 85% Vermiculite mixed with 15% Clay, 3" around/ under/ over the burn tunnel. It sat inside for two days while i mixed/ cast the heat riser. I used 6"x34" stovepipe inside a 14" diameter grease drum for the heat riser.

After re-reading Matt's thread i figured he let his burn tunnel dry for two days before gently firing it. Last night was at least two days so i fired mine. Within 10 minutes the tripwire and part of the ceiling collapsed. Just looked at the casting a bit ago and it's dry and crumbles easily...maybe they sold me the wrong type of clay? Dunno...

I've got vinyl sign work to do today for customers...$$...But tonight i'll try to build another with ceramic tile above and below the burn tunnel and storebought firebrick comprising the sides of the burn tunnel, re-using the vermiculite all around for insulation. The tile may crack from thermal shock but we'll see.

While it was working last night a friend came over. We noticed just with a temp 6" duct heat riser almost no smoke was making it out, it burned it all up. :)
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Re: Newbie - Rocket Mass Heater Build

Postby matt walker » Fri Jun 15, 2012 3:34 am

Thanks for the update Oddmar, you are on your way. I wish I knew my mix ratios. My gut tells me it was more clay rich than that mix, but I really don't know. If it continues to crumble I would suggest trying a bit of straw in there to bind it all together. It will burn away in the first inch or so, but I believe it would hold it together until you got the whole unit in place and cobbed in. The tiles will crack, but may also hold everything together long enough for it all to set up. If you can find light firebrick that will improve the performance over regular firebrick, but I imagine it will work well either way. Keep us posted.
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Re: Newbie - Rocket Mass Heater Build

Postby Oddmar » Wed Aug 01, 2012 1:12 am

I've been wanting to post an update for awhile, but after my original attempt fell apart i wanted to wait until i had completed a successful unit before posting again. Well...

IT LIVES!!!

Original design where the ceiling of the burn tunnel collapsed...

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Building the riser that i just re-used for the new RMH.

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This is my new build. I'm using firebrick glued together with Rutland refractory cement, standing on upside-down ceramic tile, which itself is atop 3" of Vermiculite/ clay 'slab', with concrete-board between all that and the plywood base.

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You can see i angled the top to create an inside lip for the Peterburg tripwire feature. I put two small pebbles in the cement to keep the firebrick elevated until it cured.

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I built my oven out of a 14" diameter 16 gallon grease drum, with a handleless-cast iron skillet on top like Matt did for the warming plate.

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I built myself a cold-air intake so when it's used as a furnace it won't suck cold air into the house.

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Re: Newbie - Rocket Mass Heater Build

Postby Oddmar » Wed Aug 01, 2012 4:49 am

The dolly i had it sitting on, while one of the biggest i have, was a little top-heavy and with the riser on the whole thing was gonna be too tall. So i bricked it in, then built a low-riding cart for it to sit in...2" off the floor, 32" wide so it will fit between the trim board on a 34" wide door.

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I spent quite alot of time finishing the top of the cold-air intake. I decided the Peterburg plate (the plate that channels fresh air down to the top of the burn tunnel) might eventually burn out so i made it removable. It slides down into two metal slots and the curled lower edge is just 3/8" below the burn tunnel roof.

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Matt said his RMH 'Really took off' when he pushed red-hot clay tiles up under the heat riser, so i made a 1/4" plate that sits just above the bottom of the burn tunnel under the heat riser, figuring it will get really hot and help the convection process. It is angled up to round off the back bottom corner to ease the flow of hot gases up into the vertical heat riser. Also shown is my output port. It interfaces with the bottom of the drum and keeps vermiculite from sifting out the side of the brick wall.

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To cap off the rear of the brick box and keep the loose vermiculite where it belongs, and because my burn tunnel didn't quite come up to the top of the bricks, i used 1/4" plate under the drum.

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Bottom finished ready for a bit more vermiculite, some mortar, and then the top.

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Completed. I tack welded the riser down to the 1/4" plate so it didn't shift. Wet vermiculite/ clay mix was poured in a disk shape between the plate and riser. That ring is because i made the riser a little tall. The drum will sit 1" down inside the ring on 6 tabs, that will place the flat top of the drum 2" above the top of the 6" center of the heat riser. The shiny tubes sticking up off the heat riser will temporarily support the barbecue grill experiment, before the whole thing is transported out to my friend's house for installation as a furnace.

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Wood burning merrily in the feed chamber. I was soo relieved it worked as planned.

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Barbecue grill attachment sits down around the heat riser, with (3) 2"x4" holes on the bottom of that 55 gallon drum section to allow it to breathe...and to allow it to fit closely down around the heat riser while still allowing the 3 spacer tubes to fit up into the grill to support it. Two pieces of expanded steel mesh hold lava rock between the top of the heat riser and the food.

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I grilled some chuck steak last night. A little drier than usual but still juicy and sooo delicious. It's very nice to be able to use sticks and non-treated lumber instead of store-bought charcoal or propane. My retired Marine friend Ron was by this evening, and was Very surprised that when the RMH is going there is only clear hot gas escaping the top of the heat riser, no visible smoke. We barbecued some chicken (I've never barbecued chicken before in my life) and the magnetic thermostat on top the old Weber grill lid usually read 300-350°F. I left it on too long and dried it out too much. The meat inside was really tender though. Wednesday night i'll do 20 thighs, and use a different recipe.

Yay!! Success!!
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Re: Newbie - Rocket Mass Heater Build

Postby matt walker » Wed Aug 01, 2012 4:19 pm

HELL YES!!!!!!

Jake, you just brought a huge smile to my face! That is such amazing work, and shows a wonderful sense of innovation and exploration, I freakin' LOVE IT! You have skills my friend. Great work, just great.

If I may offer a couple suggestions, I imagine you have already thought of these but I'll just throw 'em out there:
The cold air intake is awesome man, really cool concept and execution. I believe you will want a way to close it or limit/restrict it. Mainly to keep it from rapidly cooling the mass when the heater is not running. For that, a "male" plug that just drops in the feed may be the ticket, as it would block both cold air intake and house air from leaving the room. Also, there are times that you just can't feed it that much air or it "burps." It's because the air is rapidly expanding in the riser as it heats, so the volume of air that enters the feed is too much for the system as it expands. Due to that it is sometimes necessary to limit how much air enters the system while it's burning. In a simple system you just slide a tile or something over the feed, but in yours you will maybe need to baffle the cold air intake. Maybe not. Just a thought.

For the BBQ/cooker, have you watched my latest video? I'm finding it's really useful to still have a basic RMH type set-up so you can baffle how much heat gets into the BBQ, shunt that heat to the barrel, and thus control the cook. You might consider a temporary barrel with a hole in the top and an adjustable baffle over the hole that feeds into the cooking chamber. I'm finding it's really flexible, and by shunting the heat down into the barrel you give a lot of the particulate a chance to drop out of the heat path so the cooking is really clean, not to mention you can infinitely adjust temp. I'm now thinking that the rocket core+barrel configuration is kind of a "power head" for attachments. Close it all the way off, you have RMH+hot stove top. Open it up, direct cooking. Or anywhere in between. Lots of things can be put on top; Oven, BBQ, Smoker, Large Boiler, Hot water attachment, etc. The barrel configuration gives the ability to baffle and shunt the hot gasses, which I think is a game changer over all the direct rocket cookers out there. Not to mention the barrel is the perfect support for the "attachments." My next is going to be a relatively small and light cob oven on some Backer Board that can be set up on the barrel to heat and then baked in like a regular cob oven. Open baffle to heat, close to bake. Or something.

Anyway, I'm rambling. You made my day man, I'm so excited to see your progress. I wish I was closer, I head right over to see that thing go. I bet it burns awesome.
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Re: Newbie - Rocket Mass Heater Build

Postby matt walker » Wed Aug 01, 2012 4:22 pm

Ok, I'm kinda freaking out, that is so AWESOME!
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Re: Newbie - Rocket Mass Heater Build

Postby Oddmar » Thu Aug 02, 2012 8:55 pm

Matt, on my computer screen the right side of my pictures is chopped off, and most of the time only half of the pics load, the missing ones being indicated by a placeholder named 'Image'. What up wit dat?
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Re: Newbie - Rocket Mass Heater Build

Postby matt walker » Thu Aug 02, 2012 11:56 pm

The forum software sorta crops the images depending on your screen size/resolution. If you "ctrl/+" or "ctrl/-" to change your text size on the page, you will see the crop changes depending on which way you go. It's built in to prevent a large image from blowing the page all horizontal. You can also right click and "view image" to see the original framing.

As for only half showing up, I'm not sure, I imagine it's a loading issue. I see them all each time I've come to this page, but they do load pretty slowly. Perhaps either your d/l speed is slow, your photo hosting site is busy/slow, or something?
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Re: Newbie - Rocket Mass Heater Build

Postby Oddmar » Fri Aug 03, 2012 12:03 am

I didn't know about the ctrl +/- trick...cool. I'll start saving my pics to imageshack as 800x600 instead. Thanks.
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Re: Newbie - Rocket Mass Heater Build

Postby paulbee » Sat Aug 25, 2012 8:19 am

Nice work Oddmar! Lots of interesting features on your design. Still trying to get my head around what you have down. Very nice work and I love that cart!

One observation on the initial design that failed and similar cave-in Matt experienced.

Have either of you tried a cement board product like say Hardiboard? Hardiboard might be the wrong product, but, I know I've seen one of the same company's products used in outdoor fireplace designs. Thinking about these products and others for rapid prototyping of stove concepts. Finding my limited supply of matching bricks to be rather tedious to arrange, deconstruct and rebuild :)

Other random concerns and observations
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The chimneys on these stoves remain concerning in my opinion. The inside pipe with el cheapo black pipe seems like an inevitable quick to fail point. I've seen plenty of black pipe quick failures on traditional burn systems.

Question is if the stove pipe fails (burn through) will you notice the vermiculite dump into the burn area that will happen? Concerned because vermiculite, perlite, etc. are rather small and abrasive to breathing and vision. They won't kill you, but they aren't good for you either.

Would a double wall pipe in there make more sense and how about stainless steel instead? (yes more costly).

I'd highly recommend someone try to measure the inner core temperature of the black pipe during normal firing session (unsure how you would do this - perhaps a small bore hole with a specialized thermostat wire that outputs to meter well outside there.

Finally, although you aren't seeing smoke exiting your stack there still are harmful compounds present at the end of the stack. I'd *try* to get the stack way up above head to avoid frequent blockback onto yourself while cooking outside. Know the rocket stoves in general have this myth about being "clean" and "no exhaust", but for that to be true we'd need to have these stoves blasting away upwards sustained temperature of 2000 degrees Fahrenheit.

Keep building Oddmar! Inspiring me to get off my duff and building.
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