Standalone flue gallery in steel?

[Ganlet]

I'm on year two of my build with countless hours the forum and the drawing board. The plan is 38" brick low-dome WFO, inspired by a true neapolitan pizza oven. Will hopefully start a build thread later, but have a design question for now...

Since the goal is to have it as close to a neapolitan as possible, I'm trying to keep the tunnel/opening as short as possible. Both for appearance and to have easy reach into the oven. Hence I'm planning to build a steel flue gallery that is installed outside (fixed onto the concrete slap, not shown in pictures).

I'm somewhat worried that the draw will be lacking since there are no sidewalls to lead the smoke as the common way. I've seen some similar designs, but haven't read any reviews on it. And one could say it is pretty close to the layout of a true neapolitan pizza oven, but in the real one the flue is incorporated into the insulation and gets free heating to make sure the draw is strong I guess.

What do you think about this concept and does anyone have any field-proven experience of similar design?

Sticking with the concept, an alternative installation approach is for me to attach it to the internal steel buttress (green in pictures), here it would get heated automatically to maybe create strong draw. But I believe this would act as a heat zink for heat retention after use, which is one thing I'm trying to optimize with the tunnel/flue design. Don't you think? Other cons, need to have steel going through the insulation/render, i.e. expansion cracks, worse waterproofing, etc.

[MarkJerling]

I can't see why it can't work, provided your steel flue "gather" is wide enough to catch smoke on the sides. I'd therefore suggest that you shape the "gather" wider and less deep front to back.

[david s]

Many ovens use a sheet metal flue gallery and it has its advantages. I worked on a mobile oven recently that had one and it worked well. Because of the low thermal mass you don't have the problem of a heavy brick heat sink sucking heat away from the dome. I've not seen any with no sides like the one you propose. I think that would be fine if the oven is indoors, but an outdoor oven needs to cope with side winds around the mouth and would be better if that can be arranged. Perhaps even if they could be hinged to allow some adjustment if and when required. Stainless is a preferred but more expensive material.

[Ganlet]

Many ovens use a sheet metal flue gallery and it has its advantages. I worked on a mobile oven recently that had one and it worked well. Because of the low thermal mass you don't have the problem of a heavy brick heat sink sucking heat away from the dome. I've not seen any with no sides like the one you propose. I think that would be fine if the oven is indoors, but an outdoor oven needs to cope with side winds around the mouth and would be better if that can be arranged. Perhaps even if they could be hinged to allow some adjustment if and when required. Stainless is a preferred but more expensive material.

Thanks for taking the time to reply with your experience. Not exactly what I wanted to hear, but I hear what you are saying and are afraid of the same problems. Since it will be placed outdoors, freely exposed to the winds...

The concept though, should be quite similar to the classical neapolitan ovens with a short mouth/tunnel and a overhanging flue. However I can't find a lot of examples where these are placed outdoors, maybe for a reason...

About to cut the floor insulation and order the sheet metal work tomorrow, so need to decide sooner than later.

The two options right now are to just go for it and see how it works or build a full regular tunnel with a chimney (the boring way in my eyes, with other challenges and cons).

Right now I'm leaning to the first option, and if it will work really bad I'll just have to rework it afterwards with some steel sides or expanding the tunnel and incorporate the chimney.

If anyone had some last feedback that would be reassuring or questioning, that would be much appreciated.

[Kvanbael]

My oven has a stainless steel flue with sidewalls, it is not attached to the dome (only sealed) and instead is bolted on the heart. Works like a charm!

Even with the sidewalls a steel flue improves the reach, as the entry doesn't need to be more than 10" deep. I wonder if omitting the side walls would really improve the reach a lot as would still bump your head against the top. For outside use, the side walls also protects against side winds. (I guess it all depends on where you position the oven).

[Ganlet]

My oven has a stainless steel flue with sidewalls, it is not attached to the dome (only sealed) and instead is bolted on the heart. Works like a charm!

Even with the sidewalls a steel flue improves the reach, as the entry doesn't need to be more than 10" deep. I wonder if omitting the side walls would really improve the reach a lot as would still bump your head against the top. For outside use, the side walls also protects against side winds. (I guess it all depends on where you position the oven).

Due to the low dome, I'll need to have a rather low/small entry, hence the worries of reachability with the long tunnel. It won't get any easier the longer it is at least

Been going a lot of back and forth, I strongly believe the stated design would work and be efficient in terms of optimizing unnecessary mass to be heated. However soot and the brick arch feels like a bad combo.

Now however, I'm planning to go the safe boring way with a classic tunnel opening. Or maybe the middle way with steel sides as proposed. Problem with soot still remains here though...

Anyone have any reference/feeling of the heating time with the options below?

1. Bulky tunnel opening
2. Bulky tunnel opening with thermal break (don't know if I'll able to this in a secure way though)
3. Steel low mass tunnel with thermal break

[Kvanbael]

Any flue will get soot on the inside. Not sure what the problem is with that.

And intuitively I would say that thermal loss from a flue would affect the cool down curve more than the warm up time.

[Gulf]

On startup the flue gases are rich with creosote causing the soot buildup. The oven chamber will get up to dome clearing temps. However, the exhaust gases are then mixing with cool outside air at the oven entry. The exhaust column is too cool to burn off what has already been deposited in the chimney/flue.