Rocket bread oven in existing BBQ-site with salvaged oven

Hi fellow permies.

I decided to build a bread oven in an existing BBQ-site, using firebricks for the core and a salvaged electric oven as the oven part.

Here's a video of the first burn after dry stacking the J-Tube:

No smoke, I was quite content.
I then tried to make the whole setup a bit smaller and stacked it again, this time using the energy to cook some lentil soup.

I'll keep adding to this post as the construction continues.

It's done! Had a trial run yesterday and it worked quite well (after an incident with resin rich pine )

Now I'm reviving the sour dough and really eager to start baking.

Also a little bit of cob work, maybe plastering left.

Any questions, feel free to ask!

Benjamin, I love what you're doing there!
Do you have a deflector plate or any mass inside the oven?

Hey William,
thanks a lot!
I put a "pizza stone" in there. A 35cm x 35 cm tile of refractory material. It seals in the back, as to not let the hot gases short circuit.
It worked quite well, though I hope to get a higher temperature once the whole cob etc has dried out.

Tonight we're having a pizza party!

Pizza party was a great success. We made 12 pizzas in total, taking between 3-5 minutes per pizza. We used 1,5 buckets of wood for it, the fire got very hot. I am really pleased with it.

I find this build very inspiring.  I had a smallish electric oven that mounted in a wall cabinet that no longer functioned that I was considering doing something like this with.  Unfortunately, it was destroyed in the process of removing it from the wall.   So much for my plan!  But your results clearly show that an oven can be repurposed in this way with very good results.  It is a white oven, and I think that is a big plus.  Have you thought about putting a thermometer on it?
Thanks for sharing!

Wait, is it a white oven?
I thought the gasses hit the bottom of the refractory tile and streamed up and around it before exiting out the back.

This electric ovens does seem to consist of inner and outer steel boxes, with insulation in between the two.
Perhaps you could make  a white oven by removing the insulation layer and running hot gasses through the emptied space.

William,
it is a black oven (the only white thing about it is the outside). You describe the way it works perfectly.
And yes, the electric ovens are basically 2 metal boxes with some insulation in between. I wouldn't use them to make a white oven but rather stick to the true and tested white rocket oven made from 2 oil barrels.

Thomas,
thank you for your kind words.
Sorry to hear about your oven being destroyed. I got this one from a second hand store for 7€. I'm sure you could find one for free or very cheap at a junk yard, as you basically only need the structure and it doesn't have to work.
Yesterday the thermometer arrived in the mail. I'll update you about the temperatures next bake.
I made some bread the other day and it was done quicker than in my conventional oven, so I expect over 250°C (480 F).

Benjamin.  I see I misunderstood the part of it being a black oven.  But isn't it true that by removing the insulation and directing the flue gases around the outer oven shell, the oven will still heat up, though perhaps more slowly?  That had been my plan.  To direct the post-riser flue gases around the oven, keeping the interior sealed off from the smoke.

It might work, but it also could be that the gap is not big enough. Also my inner oven box wasn’t all that sealed, lots of holes, that would then let flue gases in.
Also you would have no insulation then, probably loosing as much heat to the surrounding as you get into the oven.

Maybe you could plug those holes with refractory cement?
I think RapidSet cement could survive those tempatures, and its cheaper than refractory.
Set the inner steel box with the opening facing upwards and cast a slab in the "bottom".
Create an inner form and use it to cast the roof,,base and sides.

The barrel ovens generally have  have an inner barrel, outer barrel, layer of insulation and metal skin.
You could immitate that by usung the insulation that you removed and some aluminum flashing.
Ive had good luck covering rockwool insulation with a cement coating over metal mesh.

This project thread inspires me so much!
Thank you Benjamin for your genius adaptation of the rocket oven with your existing materials. I will absolutely rethink the possibilities for baking outdoors.
Congratulations on your success and please keep us informed of the modifications to your system. Did you plug the holes like William suggested?

Hi Amy.
William was thinking about a possibility to turn a salvaged oven into a white oven. I went for black oven, I like the smell of fire and mostly bake savory things.
For the last bake I added some mass (4,5 fire bricks on top of the refractory pizza stone).
It reached 400F after 15 mins and behaved really well, forgiving uneven feeding intervals. Baked the whole bread with less than a bucket of small, old, round wood.

It seems that once I included a photo somewhere in a thread as an attachment I can use the address and include it into other posts (as if using an image host).



This is a test.

PS: seems to work

Added a P-plate to protect the first brick of the roof of the burn tunnel today

Benjamin Dinkel wrote:Hi fellow permies.

I decided to build a bread oven in an existing BBQ-site, using firebricks for the core and a salvaged electric oven as the oven part.

Here's a video of the first burn after dry stacking the J-Tube:

No smoke, I was quite content.
I then tried to make the whole setup a bit smaller and stacked it again, this time using the energy to cook some lentil soup.

I'll keep adding to this post as the construction continues.

Hola Benjamin, Greetings from Tarragona!
What a lovely build!
I want to build an outside rocket oven this year and I'm very interested in and thankful for your build journey. As firebrick sizes vary country to country, I was very excited to see you hail from Spain. Can you please tell me what the dimensions are? Did you get them from BigMat or Leroy Merlin or local hardware? Any onfo on the bricks you used would be appreciated. I am also so glad to see you using an old electric oven as I want to do the same - barrels are not easy to come by but old ovens are.
I shall be following your design plans carefully!
Buenos dias
Sarah

Hi Sarah,
nice to hear from you! It's awfully quiet in the Iberia forum, I'm glad to read from someone that's in Spain too.

The standard dimensions I have encountered are 22 cm long, 11 cm high and widths from 2, 3, 4 and 5 cm (when stacked on the sides, as in mybuild). In this case I used the 3 cm thick ones. They are my favorites, a good compromise between stack-ability (stability with just clay slip) and not too much thermal mass. Also I used some recycled 2 cm ones, that I got from the repurposed barbecue area and never found anywhere else so far.
Most widely available are 4 cm.
Often they also have "half-ones", they are 5cm instead of 11 cm. I Guess in a conventional oven, the 1 cm difference would be filled with the mortar.
I buy them at a local "materiales de construccion", BigMat has them in my area. They are all around between 0,70€ and 1,00€ a piece.

As to the oven, I mainly didn't want to build a door and already had a square "barbecue" area that I wanted to repurpose. When using an electric oven, make sure to take it completely apart and get all plastic and electrical parts out. The rocket heats the oven to over 300 C, higher than in it's former life.

Barrels should be available at any car shop (taller), as they have the motor oil come in those. It is quite some work to get them clean (the paint off).

One thing I have to add: If it wasn't for the tight space I would make a longer burn tunnel and also heat riser. I do get some creosote in the oven, which means combustion is not complete.

Hope this helps a bit!

Hi Benjamin,
Thanks for your speedy reply. I work nights so my replies will always be 12 hours behind yours.
Thanks for the info on the bricks, I built a walker tiny stove inside my house using the fire bricks found locally but I had a lot of input from Matt Walker as to inside dimensions etc. I'm not good at figuring things out myself! I used clay slip for the core and a cob mortar using my clay soil, some sand and my dogs clipped hair for the outside clay bricks. And I also used an old, salvaged cast iron stove front as I couldn't imagine fabricating the firebox door and fireboard is very expensive here, well, more than I am willing to spend anyway. I did fabricate the oven door (just sheet metal) but haven't used the oven.  I was unable to insulate and seal it so had puffs of smoke seeping past the door seal. I ended up cobbing the edges shut to seal. If I get around to fixing the design, it will only be good as a slow cooker or smoker. I tested the temp and it wouldn't bake anything succesfully. I cook mostly on the stove top in winter and it has a built in water boiler I found 2nd hand. And it keeps our little casita lovely and warm. I am thinking of posting a build diary like yours but that's a lot of work- which is why I am so grateful for yours. I suppose I just don't feel confident enough to post it. If people start asking technical questions I'll be lost as I literaly just followed the plans!

My stove has been in use for one half and a full winter now and. Last winter it was only used from January to the end of February but this year we started using it in November. I removed the glass top in October and there wasn't too much soot in the innards. It will be interesting to see what it's like after a full winter. I have some creosote condensation streaks around the outer chimney but that may be due to damp wood I or issues with my secondary air intake.
I've bought a lot of rockety stuff from permies but the height of their oven was a bit high so I was pleased to see your modification and your measurements are metric so I don't have to convert! What's the height of the door of the oven when it's open? My mother is only 160cm tall and she's getting on so I dont want to risk her having an accident. Ideally I'd like my oven door to be about 120cm high when open. What was the height on your initial riser?
While I love my indoor Walker, I don't think it would reach the temps needed for breads even if I put the oven directly above the core exit. Mine doesn't burn too efficiently either - I think it might have something to do with the 2ndary air intake's size or position. I don't get flames shooting out the exit causing the stovetop to flicker- I think that looks cool- and it's not entirely smoke free. I need something that is very efficient and burns clear because if anyone sees a plume of smoke in my area, they will get the bombers out before my bread in even in the oven! I know that my fire is safe, but fire is fire here in the summer. I want to add a separate j tube with the double ring cast iron plate that came with the stove front for frying/boiling etc.I haven't worked out yet how to position the plate over the riser. I'm building an outdoor kitchen so it will have 1m walls with mesh to the roof and I'll put a spark arrestor over the vent. You vented your oven straight out the back, did you go up and add a chiney pipe or did you vent it facing down?
BTW, what is the insulation you used called in Spanish, how is it sold, by the roll or sheet? My spanish isn't great and trying to make myself understood is a trial for me and the other person.

You're right about the Iberian forum, it's very quiet. There are a lot of people using permaculture techniques in my area and there are local facebook sites but most are more about permaculture gardening, swales etc and not so much about building/heating. While I am a keen gardener with an interest in being self sufficient, there is more to living than gardening! I'd be really keen to swap ideas about linking household grey water to outside food producing areas, other than mulch pits, maybe incorporating aquaponics or at least some aqautic wildlife habitat, how to combat the mosquitos and midges, beat the heat in our summers and offgrid heat (other than butano on demand units) plumbed into the house. Share successes, experiences and especially our failures. Yeah, all things relevant to our corner of the world.

Hi Sarah!

Sarah Joubert wrote:I suppose I just don't feel confident enough to post it. If people start asking technical questions I'll be lost as I literaly just followed the plans!

For me it's the other way around. If you're not sure, the lovely people here help you. And double check what you're doing.

Sarah Joubert wrote:What's the height of the door of the oven when it's open?

The oven sits at about 80 cm from the floor. 10cm foundation and then 70cm riser.

Sarah Joubert wrote:What was the height on your initial riser?

What do you mean by initial? It should be around 70cm.

Sarah Joubert wrote:I need something that is very efficient and burns clear because if anyone sees a plume of smoke in my area, they will get the bombers out before my bread in even in the oven!

When I use small, dry wood I have a tiny bit of smoke in the beginning and then none after 5 mins of burning. Not enough smoke to alarm anyone. Where I am barbecues are allowed (on a 10x10m concrete patch), so no problem using an outdoor oven. Maybe a 5 minute riser, like this one, with Morgan Super Wool would get smokeless even faster.

Sarah Joubert wrote:I want to add a separate j tube with the double ring cast iron plate that came with the stove front for frying/boiling etc.

That sounds cool! You can always partially build the J into the ground, or raise the floor around it.

Sarah Joubert wrote:You vented your oven straight out the back, did you go up and add a chiney pipe or did you vent it facing down?

Out the back with a 90 degree elbow, then straight up. I need to figure out a little top to prevent leaves and rain to fall in.

Sarah Joubert wrote:BTW, what is the insulation you used called in Spanish, how is it sold, by the roll or sheet?

In this case it's just RockWool, lana de roca, sold in sheets. I do have some Morgan Super Wool now, but for the outside of the burn channel and riser like I built in this case RockWool is good enough. It's not in contact with the flames.

Sarah Joubert wrote:Share successes, experiences and especially our failures. Yeah, all things relevant to our corner of the world.

More than happy to do that in the forum!

Hi Benjamin,
Thank you for all the info, that'a great help.

Yes, Permies is great for getting answers- this thread is a case in point! I have asked for, and received, help many times in the forums. Folk are always keen to help. And I would create a thread solely to encourage others to try because I had absolutely no experience with cob, firebrick, fire science etc when I started the build. My point was: even after building it, and it working fine, I wouldn't be able to explain why. Matt basically wrote an idiots guide and I followed it. I might dig out all the photos I took and document the build.

You mentioned that you downsized the standard J tube but kept the correct ratio so was the height of the original riser tallet than the final 70cm?

As for keeping rain and leaves out, I have seen various "hats"that keep the rain out and deflect wind. Some of them have a fine mesh spark arrestor that should stop leaves too. They fit the standard pipe sizes available in spain. I bought on for 12E from my local hardware but I'm sure you know what I am talking about. Do you have something different in mind?