Thoughts on using a pizza oven as a firebox for a brick smoker?

[copper4X]

Another update (year and half later). We're actually getting closer to finally building this thing. Took some time to convince my dad it was a good idea, but that's besides the point.

One thing we're unsure of, is how we should do the roof of the smoke/grill chamber. I would like it to be flat, because heat rises so having a big cylindrical roof would leave a lot of space for heat to just pool in. Maybe we can use refractory concrete? Maybe have rows of brick supported by angle iron.

Just a reminder that the grill area/smoke chamber will be styled like a Argentine parilla. Except it will have doors on it (otherwise wouldn't work very well for smoking).


This is my latest 3D model, in case that helps any. I did not bother taking the time to draw out a roof, the intake from the firebox to the smoke chamber, or the chimney that would be on the far right to make it like an offset. The model was mainly just to work the main dimensions of the base out.

We went with a barrel style oven/firebox to keep things simple. Plus my dad is strongly considering building a separate purpose built dome pizza oven. So this things main focus will be smoking and grilling.

[UtahBeehiver]

How do you intend to use the pizza oven, large parties, or small gatherings? I have a 42" oven and I rarely fire it up of just the two of us but for larger parties it is good. I do not make large diameter pizzas, mostly in 12" range, they cook so fast there is really never any wait and typically cook 2-3 at a time. JR Pizza built a 39" diameter and is one of our moderators with a well documented build.

[david s]

I meant efficiency in terms of fuel consumption per chamber volume. A larger oven will have more thermal mass, but wall thickness also comes into play. Contrary to your assumption that a larger oven will take longer to heat, in practice there’s little difference because the spread of heat by conduction is at the same rate for the same wall thickness. Ovens of different sizes, having the same wall thickness will have the same heat up times. A larger oven will have a larger fire. In terms of efficiency it’s similar to the comparison on fuel consumption between a 1000cc engine and a 5000cc engine. The bigger engine uses more fuel, but nothing like 5 times more. The larger chambers are just more efficient.

[copper4X]

Build it and share yor journey so members here can also benefit.

May be a while before that actually happens. But hopefully it does.

When it does get to that stage I'll probably start a new thread here:

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction

Which appears to be the forum for new builds.

[copper4X]

Generally the larger the chamber the more efficient it will be

How are you defining efficiency here? Because a larger oven will hold its heat longer, simply due to larger thermal mass. But, I assume, it takes more fuel to get it to a certain temperature. And I assume, that even though the larger oven will hold its heat longer (again due to larger thermal mass) it also should be losing heat faster with more surface area. But it gets complicated and confusing because while it may technically lose net heat faster, it also has much more heat to lose with the larger size. So it probably ends up holding its temperature longer.

So, I think maintaining a certain temperature with require more fuel in a larger oven. Which is perhaps ironic, considering that it holds heat better. But it also requires more fuel to heat up. Basically that extra thermal mass works for and against you in certain ways. More thermal mass means slower to heat up, but also slower to cool down.

Heat transfer is complicated though, so I may have something wrong there.



My main important question though, is which oven size takes more to heat up, 36 inch or 42 inch? And how much is the difference in wood consumption.

With all that said, you're making me think maybe a 42 inch oven wouldn't be a bad idea. I was sort of leaning towards the 36 inch when writing my last post.

[david s]

I think your idea is pretty good, but there's really only one way to find out how successful it will be.

Smoke is unburnt fuel. A crossdraft hemispherical chamber is very efficient. So much so that once it's well heated (from about an hour) there's virtually no smoke. However, holding the temperature much lower, it can easily be made to generate a lot of smoke.
Generally the larger the chamber the more efficient it will be, but for smoke generation you really need inefficiency.

Understanding how heat travels should give you a better understanding of design features.
Heat travels in three ways

1. By convection: (movement of air) like a conventional kitchen oven. As hot air expands, it rises. The heat from a fire in a WFO rises by convection heating the crown of the dome first.
2. By conduction: The more conductive the material (thermal mass) the quicker the heat will travel. It moves equally well in any direction by conduction.
3. By radiation: again it will travel equally well in any direction. Radiated heat can be reflected.

The heat from a fire in a WFO mostly travels by convection, but also some by radiation. The dense conductive dome stores that heat as thermal mass and the heat spreads via conduction to all parts of the dome and floor.. To retain the heat, the inner dense dome and floor must be insulated to reduce heat loss.
Once the inner oven parts are well heated the oven re-radiates its heat back into the chamber. This cooking via heat radiation rather than convection is, I believe, the secret to why WFOs cook differently, and so much better than convection ovens.

I'm not convinced that a WFO of this type is the best solution as a smoke generator, but I think you could make it do both functions. Build it and share yor journey so members here can also benefit.

Regarding your other question, refractory and firebrick have the same characteristics when fired in place to service temperature, but as a WFO service temperature is far lower than the manufacture of a firebrick, it is less dense and less durable and hence less efficient than firebrick, but it works and is far cheaper, far simpler and far quicker than brick building.

[copper4X]

I also wanted to ask for thoughts on how large to make the pizza oven itself, as well as type on materials. The CAD file above I did 42 inches and a high dome. The PDF stated that a high dome is more efficient. And since I would be using this as a firebox for long smokes, efficiency is very good. High dome does raise the height of the smoke chamber (since that's based off of the opening above the brick oven). But that's a small downside for being more efficient.

How much more efficient is a 36 inch vs 42 inch? I've seen some even mention having a 32 inch oven. But I don't think I want to go that small. I would like the option to cook a new york size pizza. Which are typically 18 inches. A 36 inch still has a 19 inch opening, so I assume a 36 inch oven should still be able to cook that I think. I'm very curious how much less wood a 36 inch oven uses vs 42 inch.

Is refractory more efficient than firebrick? Or is building the oven efficient mostly about insulation. I assume good insulation is what mostly matters. As well as size and dimensions of course. Is it worth insulating underneath the oven floor? I don't know how expensive the insulation is, but if it's not terrible than I would consider just going crazy with insulation around the smoke chamber too. To make the whole system more efficient.

[copper4X]

Over a year later, I finally made some progress on this. I have access to AutoCAD at work, and in some free time I learned how to 3D model and got this far:

This is not complete yet. I haven't designed a roof for the smoke chamber area. But I plan on doing that later when I have some more time. I'm thinking a cylindrical roof would be best. That would make for good airflow in the smoke chamber, and you could make the roof out of bricks and it should hold. At least, I've seen people make ovens with a half cylinder roof. I also plan on having some doors on the side to close off the smoke chamber and access it.

A little explanation on how this would work, is you'd have a valve/dampener on the hole going out of the top of the dome into the smoke chamber. So you can simply close that off, and it would basically operate just like a normal pizza oven if desired. And if you open that dampener, then you basically got an offset smoker with using the pizza dome as a firebox. I would also want a dampener on the back chimney, to control air flow while smoking. You would lose some heat efficiency through the closed dampener of course. But I assume the loss wouldn't be too much of an issue. Especially considering some ovens put the flue right there, and are still able to cook hot enough.



The smoke chamber I think would be fine mostly with normal brick, and just a fire brick floor. Similar to the Argentine style brick grills you see:

They just make the floor and a foot or so around the side fire brick. I assume that's OK.

I do plan on having this where the smoke chamber could operate independently as a grill, just like these Argentine grills you see. Otherwise none of it would need firebrick, if I was only ever using it for smoking at 200-350 degrees or so. So I'd want to be able to burn down wood into coals, and then shovel them into the smoke chamber floor and grill stuff over wood coals like they do in South America. Closing off the dampener between the dome and the smoke chamber, using the dome as a firebox to burn wood down to coals for the grill/smoke chamber area.

I'd also consider doing direct heat smoking in the smoke chamber. Pretty much same thing as the paragraph above, burn coals in the dome. Have the dampener between the dome and smoke chamber shut. And shovel the coals into the smoke chamber for direct heat smoking.

So a lot of different possible functions from this design, that I think would all work well.

I probably should've finished the 3D design before posting this, but I wanted to go ahead and share. And gather anyone's thoughts/opinions/concerns etc.



I'm curious to know if it's recommended to have any kind of valve or dampener in the flue in the entrance to the dome.

[copper4X]

Does anyone have blender models of a fornobravo pizza oven? I searched blender on the site and just got people talking about using an actual blender (go figure).
If anyone has any other modelling software suggestions over blender, that's also fine. I just like FOSS.

I live in an apartment, so won't be able to build anything till this housing market gets better (or if I talk my dad into letting me build a brick oven/smoker at his house). Hence why I'm only just now bothering to work more on this idea conceptually.

In the meantime I want to try and make some basic models on what I'm considering building.

[david s]

FYI, A chimney going through the top of the dome is not a very efficient thermal design. Be sure to look at the free eplans from Forno Bravo on dome ovens.

Whilst a central flue at the top of the dome (updraft system) is not particularly efficient , it does have some advantages. Having built a number of kilns, I was fairly familiar with updraft, cross draft and downdraft systems and was drawn to the Roman kiln designs (central flue in the centre of a hemispherical chamber) for a wood fired oven.
When firing their kilns with the chamber full of wares, the flames had plenty of chance to heat those wares before exiting at the flue. Unfortunately firing an empty chamber as we do with our ovens the flames leap straight for the flue and a fair amount of heat is lost. By having a cross draft system as in the type of oven most builders here build and use, the flame is drawn across the roof of the dome then pulled out at the door, before exiting into the flue. This uses the full length of the flame with less heat loss. The downside is that you have an entry to work past making access and management of the oven interior more difficult. The central flue updraft system has no flue gallery and is far easier to work.
Also as all oven owners have found, their ovens are quite smoky at start up until the flue develops enough power through heating to provide sufficient draw to suck the smoke out and prevent it from going out the front.
When visiting Pompeii I was surprised to see many small updraft ovens inside individual homes. I thought they all would be modelled on the famous large oven which was the Bakery, the oven the so called Pompeii Oven was modelled on. Pondering this discovery I realised the reason. You would prefer an oven that was a little less efficient to one that smoked up your whole house. For a commercial bakery that would be fired every day and probably never cooled down, a more efficient system would be the better choice.
Today nearly everyone has their ovens outside, so the smoke issue is far smaller than the efficiency one.
Many, usually first time builders, think they can come up with an improved design without realising that there have been billions of solutions experimented with over the past few thousand years and the popularity of the hemisphere with a front, cross-draft flue, consistently comes out the winner.

[copper4X]

There is a YouTube video of a guy who built a WFO / smoker combo. He did the opposite of what you are suggesting though. The dome of the WFO is the smoke chamber with a separate fire box feeding it. I actually found this forum because he mentions it in the video. I haven’t come across a build thread for his oven on this forum though.

https://m.youtube.com/watch?v=Y2vuY2kL5bw

This is a very cool build, and I believe I have seen the video before. What he made is not not dissimilar from a lot french brick ovens. Those seem to often have a firebox. Sometimes right below the main oven, and sometimes kind of to the side and below.

https://www.youtube.com/watch?v=8oiAbC-wOds

This video is one such example. When I first saw one of these specific brick ovens my very first though was how it was similar to an offset smoker.


The reason why I didn't want to go with that idea is because smoking in a dome would be totally different from a typical steel offset (or the cinder block smoker I made). And I'm not sure if it'd work well for brisket. For brisket (and not just brisket, but it's my favorite BBQ meat, so I'm using it as the example) you want all the hot air to flow over the fat cap. And you want to avoid heat coming form the bottom, or pretty much any other direction. There are also of course direct heat smokers, where you'd smoke the brisket fat cap down, and all your heat would come from the bottom and only the bottom. Either way, you want a very predictable flow of hot air, so you can position your meat correctly. In a dome, I don't even know how the airflow would work. Personally I really would not want to smoke a brisket in a dome oven.

Now don't get me wrong, you can of course smoke things that way. Heck, you can apparently smoke in a normal brick pizza oven. But I doubt I could get as good of brisket in something like that, than I can in the cinder block offset smoker I made. I first started smoking briskets on a green egg. And I made some decent brisket. But once I built the cinder block smoker, the brisket I made was much better. Shouldn't be a surprise, it was purpose built for it unlike the egg.


With my version of having the firebox and pizza oven be the same, the smoke chamber can still be purpose built for good airflow.

[UtahBeehiver]

FYI, A chimney going through the top of the dome is not a very efficient thermal design. Be sure to look at the free eplans from Forno Bravo on dome ovens.

[NewEnglandNewb]

There is a YouTube video of a guy who built a WFO / smoker combo. He did the opposite of what you are suggesting though. The dome of the WFO is the smoke chamber with a separate fire box feeding it. I actually found this forum because he mentions it in the video. I haven’t come across a build thread for his oven on this forum though.

https://m.youtube.com/watch?v=Y2vuY2kL5bw

[printheineken]

I have a offset smoker I made from cheap cinder blocks, which obviously isn't very sustainable and will fall apart some day. So I was considering making a new more permanent smoker with brick. And that got me thinking, why not just make the firebox basically the same design as a pizza/brick oven?

Specifically I think connecting the flue straight into a smoke chamber (which would have its own stack of course) would work best. On the smoking side of things I am fairly certain this would work. You can make a smoker out of pretty much anything after all. I don't think the firebox getting too hot would be an issue. You can always control how much heat is going through by how much fuel (wood) you're giving the whole system.

The connection from the firebox to the smoke chamber would be similar to how the goldee's offset works. Where they just have an angle pipe connecting their firebox and smoke chamber. Except of course that's all metal, and this would be brick.


I'm not sure if the flue from a brick oven really has any serious restraints. Outside of needing to draw some air. You see people have all kinds of different flues for their pizza ovens. Some indoors and basically a chimney. And some very short. So I assume as long as the flue is drawing air well, it's good. If having it permanently connected to a smoke chamber is a potentially bad idea, I could simply have a damper to open the flue up right above the oven/firebox. Which might be a good to have anyways, I'm really not sure.

Assuming there is nothing wrong with this idea, any thoughts on what type of brick oven to use?
I sort of naturally gravitate to the more square designs, because that's just what a smoker firebox normally is. But, after reading the forum a little it appears the round design is more efficient at heating up. And I think a round firebox is just fine. Also appears using refractory creates a more efficient design than just brick. Probably the biggest question would be what size to go for. And for that, I am really not sure at all what size I would want.


I appreciate any opinions or concerns about this idea.

Your idea of combining a brick oven design with an offset smoker sounds intriguing! The concept of using a round firebox and considering refractory material for efficiency makes sense. The damper idea for flexibility also sounds practical. As for the size, it depends on your smoking needs. Square or round, both can work well; it's a matter of personal preference. Just ensure proper airflow for the flue, and you should be on your way to a unique and efficient smoker. Good luck with your project!

[copper4X]

I have a offset smoker I made from cheap cinder blocks, which obviously isn't very sustainable and will fall apart some day. So I was considering making a new more permanent smoker with brick. And that got me thinking, why not just make the firebox basically the same design as a pizza/brick oven?

Specifically I think connecting the flue straight into a smoke chamber (which would have its own stack of course) would work best. On the smoking side of things I am fairly certain this would work. You can make a smoker out of pretty much anything after all. I don't think the firebox getting too hot would be an issue. You can always control how much heat is going through by how much fuel (wood) you're giving the whole system.

The connection from the firebox to the smoke chamber would be similar to how the goldee's offset works. Where they just have an angle pipe connecting their firebox and smoke chamber. Except of course that's all metal, and this would be brick.


I'm not sure if the flue from a brick oven really has any serious restraints. Outside of needing to draw some air. You see people have all kinds of different flues for their pizza ovens. Some indoors and basically a chimney. And some very short. So I assume as long as the flue is drawing air well, it's good. If having it permanently connected to a smoke chamber is a potentially bad idea, I could simply have a damper to open the flue up right above the oven/firebox. Which might be a good to have anyways, I'm really not sure.

Assuming there is nothing wrong with this idea, any thoughts on what type of brick oven to use?
I sort of naturally gravitate to the more square designs, because that's just what a smoker firebox normally is. But, after reading the forum a little it appears the round design is more efficient at heating up. And I think a round firebox is just fine. Also appears using refractory creates a more efficient design than just brick. Probably the biggest question would be what size to go for. And for that, I am really not sure at all what size I would want.


I appreciate any opinions or concerns about this idea.