show us your rocket pizza oven!

[kundun]

for those who have seen that thread before, yes I did change it dramatically because I had to.


well, as the title says, guys (or girls) show us your rocket - pizza oven (or bread oven)
give us infos about how they work, what dimensions you used and if you would do it again...




maybe, one of you even has connections to the owner of that oven.
batchrocket.eu/en/applications#pizza Donkeys32s Rocket Stove Forum
would be interesting to know how that's working after almost 2 years of use.




thanks, michael

[pigbuttons]

You are right Michael, you like to complicate things. Good writeup with lots of good pics and diagrams.

You may want to look into batchbox designs instead of the V shape. In my experience, which is minor, because the fuel is consumed so slowly, the friction of the wood in the feed tube is too much to overcome and it does not auto-feed well. J-tubes overcome this by feeding straight down so as the fuel is consumed it just drops onto the coals. Also, since you need a long duration burn to get the oven up to temp and maintain it, a J-tube will require more tending because of the smaller feed area as compared to the batch boxes. There are plenty of batchbox success threads here and some of them are amazingly efficient and you look to have plenty of space below the oven parts to get it all in there.

In any case, it looks like you have your work cut out for you. Oh, and steel, even stainless, is a poor choice for the combustion areas of any of these designs due to the high temps in the insulated burn path. Once the flames are no longer present, steel will suffice.

I look forward to seeing how you progress.

[serg247]

get.google.com/albumarchive/103675898722989168752/album/AF1QipMIaenaSWkUL1U8xiwP_nQVojEVGyM26FHXEKOC

[kundun]

Going one step back, do you guys actually think it’s worth going for the trouble of building rocket stove to heat a pizza oven? Or should I stick to the traditional way and burn the wood in the oven itself?

Ok, the view about self-feeding systems are overall not that good. Thanks for the info, kind of doesn’t surprise me, in theory it looks good but fails in real live…
I would prefer to keep the hole in the retaining wall as small as possible, but it seems that there isn’t much of a choice than an L-feed / batchbox and therefore a bigger hole in the wall.


Did some research and reading about batchboxes now, did overlook them in my first attempt. The Petersberg-batch-box dimension thread seems to be a working systems, what would you say if I’d stick to those dimensions? Certainly, a good option for me, right?

Steel is the wrong material, thanks for confirming that. I’ve been talking to a guy tough, who makes fireclay products and was told that fireclay will not like being buried underground, with all the moisture and even some frost and then been fired up to very high temperatures. How do you see that?
That worries me a bit, as the whole project is a bit of a one chance only, as its going to be a pain to change anything after dug into the ground.


What would you guys say, if I’d go for the 150mm dimensions from Peterbergs’s table? do you think that would give me enough power to heat up the oven?
if I'd go for a 150 or 200mm system, both ask for a much longer heat riser tube than I can put in, below the oven. I only got about 80cm. How do you see the missing height?

@ serg247, thanks saw those pics before. Just a pity that there isn't more information about dimensions, temperature and if the oven works well.

[pyrolyse]

Traditional stone wood ovens are really inefficient and smoky designs. The double chamber wood oven (Google it) increases efficiency somewhat, although I think most of it is just burned off in the chimney. But I think it's almost impossible to get the 400-500 celsius you can achieve in traditional wood ovens in a design where the fire is not placed in the same room.

[serg247]

www.youtube.com/watch?v=sNpnv-1jDUY

[kundun]

Apr 20, 2017 1:55:33 GMT -8 pyrolyse said:

But I think it's almost impossible to get the 400-500 celsius you can achieve in traditional wood ovens in a design where the fire is not placed in the same room.

seems to be true, one hardly ever sees a wood fired pizza oven that isnt black. Same with the used oven that I got, the backing chamber is dark black.
Could you clarify, what do you understand with a "traditional wood ovens in a design where the fire is not placed in the same room" ?

Are you suggestion, that it is worthwhile to use a batchbox / rocket stove to heat a pizza oven?

[grga]

Well thank you for opening this thread. This is exactly what I was questioning myself a few months ago. As I had 12cm batch box cast I decided to give it a try and make Pizza/bread/etc. oven with it.

Now I have it and it is maybe too soon after couple of test baking to give a final evaluation but some thoughts are now more clear.
I like the design because:
- There is more space in the oven as there is no space required for fire, embers. Only the hole for riser.
- Burning efficiency is good, at least there si less smoke.
- It is interesting and fun to burn it.
- You can still use it in the classic way and burn the fire directly in the oven (this makes rocket of no use).

What I don’t like and were my thoughts even before making it are:
- The floor temperature is too low. Temperature of the dome can be hot (500C) during full rocket burn but not the floor. Very long burning time would be required.
- There are ashes flying from the riser to the dome and fall on your food. So you should first preheat the oven and then use it. But this in my experiments would need three or more full burns of the batch box.


Using the oven classic way I think is better. You need less time to preheat it to working temperature. Then moving fire to the side, heaving only glowing embers or small fire during to cover the losses during baking and door opening. It is cheaper (no need to complicate with the rocket) and I found that it also can burn with very little or no smoke.

Here are a few photos of my desigh. It is 70 cm in diameter, inner height is cca. 38 cm, entry opening height is 25cm. Floor has 3cm fire bricks lied on 2cm of CAC concrete and below that is 5 cm of insulation (calcium silicate boards). The dome is 4cm thick and made of CAC concrete and has now only 3cm insulation with vermiculite – I will add 5cm extra insulation with stone wool soon.
I would appreciate any suggestions how to improve operation with a batch box rocket. Possibilities I see are: lowering the chimney entry to be closer to the oven floor to force hot air to move closer to the floor or having the chimney entry in the oven floor or below it so that hot travels beneath the floor before exiting the oven - but this complicates the design... and I am not sure if it would make noticeable improvement.







Add some isolation and cover it with tiles during summer. It works very good the classic way (fire in the oven) tested it  several time. It also worked with batch box rocket but not so good and efficient for baking purpose but I will still keep the rocket and finish it when time comes.

[fzurzolo]

Looks great Grga!

I have a traditional (non-rocket) pizza oven and have been thinking about converting it to a rocket.  But I do recognize the benefits and drawbacks that you mentioned.  Perhaps one option for you to implement in your oven that may make a difference in the floor heat would be to extend the chimney internally down near the floor.  This would make the oven more of a "bell chamber where the hot gases would be trapped on top and would have to cool and drop before going up the chimney.  The internal chimney extension would have to be removable so that you can actually get pizzas in there, but you could simply slide it in during the firing period and remove it once it's baking time.  This is just a thought though . . . I haven't tried it.

For my traditional oven conversion to rocket oven I was thinking of building the rocket off to the side and directing the heat riser into the side of the oven and having the chimney exit the other side with both openings near the floor and fully closeable with dampers.  That way I can heat with the rocket, then seal everything off and bake conventionally.  For bread baking you really don't want hot gases running through the oven and taking moisture away from the rising bread.  For pizza's though, having that hot air over the top of the pizza would act as a nice broiler to get those topping melted/fried while the floor is cooking the crust.  I'll post once I get this mod up and running.

[kundun]

thanks grga, that was exactly the kind of answer I was looking for, absolutely fantastic.
that is experience that is going to help others too. Thanks for the positive/negative aspects, it does help considering if it is worth taking the effort and firing a pizza-oven conventionally or with a rocket.
I really like the "It is interesting and fun to burn it." don't we men like to play with fire? and when it burns really hot and makes fantastic sound, its even better! (my gf would just role her eyes on such a line...)

your oven looks great by the way, I like it a lot.

what heat riser diameter are you using?

for me there seem to a few main questions about pizza ovens and rockets:
- do we need the immense heat, that a rocket produces? (maybe yes, because it helps to heat up the oven fast and "clean"
- how do we get the floor hot enough to back a good pizza

i started almost the same question in another forum link and there I got a reply from Glenn who says that the oven he built works well but the heat will not be enough for pizzas.
And his suggested improvements for a next version would be "I have an L shaped combustion chamber,..... I would increase the horizontal to say 200mm x 250mm, and the vertical to 200mm diameter."

After some digging I even found a few pictures of his floor heating:
link  from where i got those links (Glenn, hope its ok to link your pics)











Here is another oven

Sadly I cant find the other link any more, because in another forum the owner of the following oven said, that it wasnt enough to heat the oven only by means of the rocket.
Here (Link to forum) he says only that he uses the rocket AND an internal fire.


It seems that a rocket pizza oven without floor heating is going to be a suboptimal construction, as much heat is needed from the button to bake a pizza.


so maybe, we'll get people to put their experience into the forum about their floor heating system?

[pyrolyse]

Apr 20, 2017 2:07:48 GMT -8 kundun said:

Apr 20, 2017 1:55:33 GMT -8 pyrolyse said:

But I think it's almost impossible to get the 400-500 celsius you can achieve in traditional wood ovens in a design where the fire is not placed in the same room.

seems to be true, one hardly ever sees a wood fired pizza oven that isnt black. Same with the used oven that I got, the backing chamber is dark black.
Could you clarify, what do you understand with a "traditional wood ovens in a design where the fire is not placed in the same room" ?

Are you suggestion, that it is worthwhile to use a batchbox / rocket stove to heat a pizza oven?

Traditional pizza oven:



Both the dome and (most importantly) the floor is super hot, like 400-500 degrees celsius.
In a rocket oven the fire is situated is another room - i.e you have a fire chamber and a baking chamber, so you only have the flame to heat, not the fire sitting directly on the oven floor and heating it.
But as seen in this video, it can be done to make a sort of hybrid:




This builder has cleverly used the flame path to his advantage, so it heats both the air in the barrel and the firebricks elevated in the middle of the drum.
 

[wiscojames]

Here's mine - other documentation elsewhere on the site.  6" batch rocket stove made of local clay. Lined with firebrick splits for durability.  I once (as in the picture) had a bench that was heated by the exiting flue gases.  Now the bench is gone and I'm not even using an external chimney.  Floor of oven is elevated 4" above the internal clay floor, which in turn sits atop the stones in the gabion. Flue gases are forced to take a circuitous route under the floor, up and along the dome, and down a 2-3 foot length of flue pipe within the gabion, and exit approximately where the bench was previously.  I can get it up to ~700F after 4-5 hours of firing, but more common for me is 450F after 2-3 hours of firing, in order to bake bread. After the bread is done, I stuff the thing full of wood to have very dry wood for the next firing. Now in its third season, it is showing wear (mainly the firebox, not the oven). I've had various roofs and tarps protecting it from direct rain.  Given that this was made on the cheap, and was my first attempt, I think I could do a lot better next time, efficiency wise and aesthetically wise.

[ronyon]

The rocket ovens and kilns presented at www.rechoroket.com/Home.html
use only simple clay rocket stoves to heat them.
I'm not sure how long it takes to get them to reach pizza cooking temperature,but they all seem to exhaust the rocket directly against a deflector plate,which is often but not always the cooking surface.
At least one of the designs uses a second deflector plate that the hot gasses are forced to go around in order to escape the oven.
Even then, the exhaust is forced to squeeze out between the pot skirt and pot that top many of these ovens.
The ovens are all pretty small,which is probably another factor.

When I bake pizza on my gas grill,I arrange layers of firebrick mere inches from the grill surface. Most of the pizza ovens presented seem to be high dome ovens. I bet smaller ovens could get hotter,quicker,and the thermal masses would be closer to the pizzas.

[tallgrass]

I'm building one next weekend, an 8" J-tube with trip wire and peter plate, perlite/clay riser and a 2" thick firebrick slab as the hearth.  I'm not sure yet on the efficiency of the unit, but it is being built in the SF Bay Area where any smoke pollution is to be avoided, so the goal was to build a smokeless oven, not necessarily the most efficient one, but time will tell its efficiency.  I would like to build a thinner earthen shell on this, maybe 2 1/2 inches instead of the 4-5 thick that I usually do for a multi use woodfired earth oven.  

[Dan (Upstate NY, USA)]

It is going to be hard to get the built up ash out of your design...