Design guidance and thoughts please! :)

[LukePricePhotography]

Hi all.. I have been planning a wood fired pizza oven for quite some time now and having recently purchased a new house with a stone outbuilding which is singing out to be converted into an outdoor kitchen!!

so to that end... I have been reading your forum and watching endless you tube videos on the topic.. I have purchased LOTS of building materials and I'm ready to start !!

but before I do... I wanted to check my dimensions with the experts and make sure my plans are reasonable!!

[UtahBeehiver]

I just approved your thread for your new project and deleted duplicate posts. You should be able to post pictures now. I do suggest you get the e-plans from Forno Bravo. They are a good base line and will answer a lot of you questions. They are on $3 for from FB. Then use the forum for addition questions and specific details. I would ask that you remove photography link out of your signature block since we try and not to promote commercial website links.

[LukePricePhotography]

Nice that you think I'm commercial !! Photography is just my obsessive hobby... actually an Aerospace engineer

I did get the FB plans some time ago... they have been really useful thanks!!

[LukePricePhotography]

Sorry to all... this is my first foray into Forums and social media ! I have to admit I'm not the best or it would appear the most patient which perhaps doesn't bode well for cooking with wood !!

Ok.. so hopefully there will now be an image of my design plans in cross section.

[UtahBeehiver]

LP,

We have not seen many separate fire box/oven combos. There have been a few designs posted here and there but I cannot recall of any that have been finished and if they have been, the end results have not been posted. Maybe others can chime in on your design. Since you are an Aerospace engineer, there are several active and retired "Engineers" on this forum, JR, WarEagle90, myself who over design and over build....LOL. Then there are real world "Street" engineers such as Gulf, SableSprings etal who build really nice ovens.

[LukePricePhotography]

So... to explain the design... Clearly a domed pizza oven with a fire box below.

My thinking on this is, if i do this design I will be able to achieve a greater burn and sustain it for longer. I will also have a cleaner and larger cooking area.

But... I'm aware that most indirect don't achieve the same temperatures as direct cooking options.. so I'm massively insulating both the firebox and the oven with loads of thermalite briquettes (brick sized 7.2kn ones)..
there will be a good chimney length between the firebox and the oven itself so the burn should be largely complete, there will then be a chimney out of the oven tunnel in the usual fashion.

I'm trying to keep the thermal mass to the areas its wanted... so the floor of the oven, the firebox lining itself and some on the domed roof of the oven.

I'm then going to completely fill the void above the dome with broken up thermalite blocks and complete thermalite blocks also. capping it off with a mortar coating.

The other element is the steel fabrication.. this is just because I'm happiest with metal so I've got a 5mm thick mild steel dome. I'll then have a 3mm tunnel and a stainless steel chimney with a capping on it.

in terms of construction, I will be building this into the corner of a stone outbuilding.. basically a brick outer skin mortared in place, then doing a tight but dry build of the thermalite blocks... the firebricks will perhaps be sealed together with a high temp sealant. over the top of the dome (which I will drill to allow moisture out) I will put a 1-2inch oven cement layer for some extra thermal mass.

Doors will be built in hinged sealing types I guess.


these are my thoughts at the moment!!

[LukePricePhotography]

In terms of dimensions I have one fixed dimension which is the internal diameter of the dome.. 800mm

(A) internal oven height I'm guessing needs to be 400 high ??
(B) height of tunnel and door is I understand 63% of the oven height so 252mm high??
(C) length of tunnel 400mm ish
(D) diameter of flue... I'm thinking 100mm diameter or should I go 150mm?
(E) height of flue approx 1200-1500mm
(F) Diameter of heat pipe 230 x 115mm basically a single brick
(G) based upon my layers around 600mm
(H) heght of firebox approx 300mm
(I) depth of firebox approx 500mm (also 400 wide ish)

[LukePricePhotography]

So to the questions!!!

1) Am I right to base my dimensions upon the standard ratios even though my air flow and metering will be different?
2) Assume I pick a door close to the ideal dimension then reverse the height of the oven to match that?
3) should the heat pipe come up centre rear of the oven floor? or should I have two coming up, one on either side to create a swirl effect?
4) if I'm surrounding the flue with insulation I don't need a double wall flue do i?
5) if I were to paint the inside of the oven dome with high temp paint, what colour would be best, I assume black is best for emissivity, but perhaps cream for improved visibility inside!
6) any thoughts on doors??

Yes I know this is a bit of a risky design, but worst comes to the worst I simply block the heat pipe and cook from inside the oven as normal.

[deejayoh]

That is probably a better design for bread (look up "White Oven") than for pizza. For pizza, I suspect your floor is not going to heat enough, or evenly - and you are giving up cooking space to a vent right in the middle of the floor.

[LukePricePhotography]

Hey, thanks for the thoughts... but it does inevitably lead to another question

for the ultimate neopolitan pizza what is the ideal approx ratio between :
- conducted heat from the floor of the oven
- convected heat from the oven air
- radiated heat from the oven ceiling

btw. the heat pipe vent would enter the cooking chamber toward the edges of the cooking floor and use a vented cast iron or firebrick drilled with 6 large holes. so I wouldn't be wasting cooking volume.

however looking at white ovens I think there is a balance I can do to increase the floor heat and thermal distribution... I can include an additional layer of firebrick under the floor, with vent paths which lead to a vent in the upper floor layer. see image

it does mean that I would be increasing the thermal mass of the oven so heat up times will be longer, but what do you think??? I could also angle the firebrick cuts to make the heat pipes an inverted v in section so there is better transfer into the lower layer first rather than creating hot spots on the upper floor..


???

[LukePricePhotography]

ok... here is the concept with actual firebricks. shown upside down so you can see the heat pipes and how they line up with the vent holes in the cooking floor.
The red circe indicates the 800mm internal diameter for the oven.

I'm thinking that with doubling up the thermal mass of the floor I should minimise the excess to the sides of the oven, so just enough to bond the upper dome oven cement to the floor.

I have staggered the layers by half a brick so there is good seam overlaps and support for the layer above.

[LukePricePhotography]

So a minor blip on my build... The outbuilding I'm going to construct this in has a slightly uneven floor. so I need to pour a new level to start the build off properley, deciding to do things like an engineer, cut it back so there is a good thickness of pour all around and well tied in seams... So I started to cut back the old concrete pour.. to find a rather large cavity lurking beneath... What I had assumed was a solid floor is actually a non reinforced 1 inch concrete slab which was poured over a wooden platform that has rotted away.. so a few more bags of concrete blast and cement mix will be required....

at least I know I will have good foundations!! it will be around 18inches deep and I'll add a layer or two of meshing too. the other benefit is I no longer need to go to the tip to get rid of the old bricks I have that are covered in mortar !!

[david s]

Unfortunately you won’t know how the design will work until you try it. Altering it once finished will be difficult. 200 years of Roman ingenuity has proved the hemisphere with front flue gallery particularly efficient. I tried two different ideas for my first three ovens before going back to the traditional design which I find superior. Please build your design and report back for the benefit of other members.

[RandyJ]

I am all for unique ideas and new takes on oven builds, but I feel you are trying to reinvent the wheel from scratch. These ovens are based on principal's that are over 2000 years old. What is it that you are trying to improve on? If you want to do Neapolitan style pizza you are barking up the wrong tree and will not get what you are looking for. For that you need a floor with low thermal conductivity and very high heat. In the neighborhood of 900F + and dome temps north of 1200F. You won't be able to do that with a remote fire. From what I have seen these ovens burn pretty efficiently and if you are concerned about wood usage a smaller lower mass oven is going to work much better. What you are designing is a bread oven not a pizza or roasting oven.

Randy

[SableSprings]

Luke, first of all, remember this is your oven and our comments are meant to be constructive. We all hope your successes (and any failures) during the design, building, and use of your oven will ultimately add to the positive, collective experience of the forum. Having a double chamber grey oven like this would work best if you actually fired in the top section when doing pizza and used the dual chamber (indirect heating) to heat the upper chamber to bake bread & roasts.

As was noted in an earlier post, there have not been a lot of indirect fired oven builds documented on this forum. The few experiences that have been shared, generally support the opinion that these ovens are difficult to bring up to the 650-750F (340-400C) considered “low to OK” (by most) for pizza. As I see it, the potential issues you may have creating a great pizza experience with your design are:

1) Mass heating. The amount of firebrick/refractory material in your design will require a very long time to bring it up to the temps for pizza. That also means that all of your refractory materials around the firebox will probably also be at pizza temps. Translation: A lot of wood & a lot of time to heat the cooking chamber to temp.

2) Metal internal oven shell. Metal will expand and contract quite a bit with these temperature swings...most likely, the expanding metal will crack and degrade the nearby masonry components in a very short period of time. Metal also doesn't do very well in the often corrosive environment of wood firings.

3) Cooking floor heating. It looks like your original design would only heat the cooking floor by radiant and convection heat coming up and over (following the dome). That will take a long time to bring the cooking floor to temp. In your second, double floor design, you would be heating quite a bit of additional mass to bring those top/cooking floor bricks up to temp...not very efficient.

4) Cleanout. Cleaning the creosote out of the firebox/flue system looks to be a serious problem. With your heated double floor design, I don’t know how you could clean it out of some of these spaces without some disassembly.

I’ve attached a couple of pictures of the classic French/Viennese wood fired oven with the gueulard firing that you might find interesting. Note the very low chamber ceiling in this vault design. I also attached a simpler grey oven design of a more classic Roman dome shape that would be much more effective in producing pizza and/or breads.