Will Fuchs

Hi again!

I've been working on and off on my oven for a bit now, got a test fire yesterday and the bent rocket riser worked! When you say simple rockwool, are you talking about this stuff? (https://www.acehardware.com/departments/building-supplies/insulation-and-house-wrap/insulation/5027137) I had read that the binder in rockwool offgasses around 600f, but that might not matter if it is contained... I am planning on wrapping the whole oven in insulation and then putting some chicken wire and cob on top of everything, for durability and looks. Do you think that this will work?

Here's a picture of my oven so far, it's been an absolute blast to build!



Cheers,
Will

Haha yeah I don't want to do any more sledgehammering than absolutely necessary!

I like the sound of the 5 minute riser, thanks for showing me that! As far as insulation on the rest of the oven, I was just planning on using an insulating cob mix. Do you think that this will be insulating enough, or should I go high tech and get some extra ceramic fiber/superwool? My only worry is that costs will add up quickly with the ceramic fiber... What did you use for insulation in your oven?

Thanks for the quick reply Eliot!

I'm trying to make my design closer to the Barker plans, but also use the base of my existing cob oven. My base is a 3.5" thick 46"x46" reinforced concrete slab on top of cinder blocks. I was considering cutting a hole in the concrete for the heat riser, but I have no experience with that, and there's a good amount of rebar in the pad. Right now, there is 8 inches of pumice and old bottles on top of the slab, followed by a layer of bricks and the cob oven. Here's a picture of the whole deal (excuse the melting cob! A light rain caught us by surprise...):





To keep the rocket stove as close to the Barker plans as possible, I could place the J-tube on the side of the existing base, and then add an elbow at the top of the heat riser to direct the heat into the bottom of the barrel oven. Here's a picture of that too:




Does anyone see any problems with the extra turn in the J-tube? The picture makes it look longer than it will be – it should only be ~8” of tube, but 24” from one vertical wall to the other.

Also, I was planning on making an 8" system, instead of 6" like in the book. A few reasons for this:

A) I'm making a deeper oven (mine will be 24" vs Barker's 17")
B) I'll have a bit more mass in the oven, with 3 shelves of 1/2" thick clay tile. All together I'll have something like 30 lbs of clay in the oven.
C) I really like pizza, and I love how my cob oven right now can make perfect pizzas in 2 mins. I'd like to have this functionality in my rocket oven, so I need the oven to get hotter than 700f. From what I've read, this seems totally possible, so long as the J-tube is big enough.
D) I bake bread at 500f and want the shortest possible reheat time between batches.

Does this seem reasonable, or would a 6" system be sufficient? I'd hate to build the whole system and then realize that I made it underpowered...

Finally, does anyone have any suggestions on what to build the heat riser out of? I'll make the burn tube out of old clay bricks, but I don't have enough to make the heat riser out of them as well. I figure I can recycle all of my cob that hasn't vitrified, add lots of pumice or perlite, and cast a riser. My only gripe with this is that the sand from the cob will make the mix less insulated...

I am located in San Luis Obispo, CA if anyone knows of any great material sources around here!

Cheers,
Will

Hi! This is my first post on Permies, though I've been reading along for a while now.

Last summer, I built a traditional cob dome oven to bake large batches of sourdough bread in. I could fit 8 loaves at a time, and could squeeze 3 loads out of a big (3+hr) firing. It's fun to use, but the amount of smoke and inefficiency are starting to bug me... I'm now thinking about building a "rocket deck oven", roughly following the plans for a white oven from Tim Barker & Joel Meadows' The Rocket Powered Oven. I figure that I can get two ~20" shelves in my drum, and if I build it 24" deep, that gives me 8-10 loaves per bake. What I'm really excited about is the ability to heat up the oven between batches (no more loaves getting overproofed while I re-fire the cob oven!!). I also like the idea of not having to sweep coals & ash out when I want to bake bread!

Due to space constraints, I'm planning on having both the chimney and the J-tube on the back side of the oven. This means that I would probably have to add some baffles between the barrels to force the hot gasses to the front of the oven. This would create a series of ducts that force the air back and forth in the oven as it works its way up, then down the back and out the chimney. What I am wondering is, should I try to keep the cross-sectional area in each duct the same as the chimney and J-tube? Will adding too many baffles interfere with the ability of the oven to draw properly? I've attached a few design pictures - the CAD ones are for the single baffle design, and the hand drawn sketch is for the multiple baffle one.

Any advice will be greatly appreciated!



The entire oven, with outer drum attached

Outer drum removed to show the baffles and vents. This is similar to Tim & Joel's design, but with a bottom vent to accommodate the J-tube in the back.

Just the baffles and chimney / heat riser.

A sketch of the multi-baffle system to heat the oven more evenly. Will this hamper the flow/draft too much?


Cheers,
Will