Half Barrel Vault Half Pompeii oven = Barrelompeii

[danmarley85]

Hello Guys,

Looking to build an oven over the winter ready summer next year (or what we have for a summer!) and was hoping to pick a few brains, any help would be greatly appreciated.

I've looked at numerous designs and build threads for ovens and one thing has stood out, I don't like the chimney/flue at the front design of most barrel vault and Pompeii designs.

With that in mind I gathered some information on chimney design for wood-fired ovens and came up with this idea.

If I were to put the chimney towards the bottom of the back of a Pompeii style dome I'd not have issue with air being drawn in the entrance oven the fire and straight out of the chimney.

I mocked up a rough draft on sketch-up to try and illustrate my idea, I'm looking to use four paving slabs as a base, lay a vermiculite/concrete slab on the paving slabs and build the "Barrelompeii" floor, walls and roof from fire bricks collected from a storage heater. Then an Ceramic Fiber Blanket and finally layer of vermiculite/concrete over the top. With the chimney I think I'd also fit a damper to seal in heat once the burn phase was over.







I'd like to use the oven to cook both short periods (i.e. pizza's) but also have enough thermal mass to cook for longer periods (i.e. roasts etc).

The pink would be vermiculite/concrete mix (extending the whole way round) and I would have a door/entrance at the front

Any comments (good or bad), advise, suggestions are welcome! I'm here to learn as much as possible before breaking ground!

Many Thanks
Dan

[cannyfradock]

Hello Dan......welcome to the forum.

I love your Sketchup designs (wish I could get to grips with sketchup).....but I disagree with your basic design.

These are my honest constructive criticisms of your design so please don't take offence........
The Pompeii oven works on a principle of known facts. Give or take a few minor tweaks....the dome is a perfect circle ...or half circle of the diameter of the base. 90cm internal diameter = 45cm dome height. The internal arch height is 63% of the dome height....= 28.35cm.

The "new" air......once there is heat in the oven, gets drawn/pulled through the entrance and gets heated and expands. This spent air is then pushed upwards and drawn around the back of the oven and curles around the top of the oven looking for an exit. The spent gases then curl forward over the top of the oven looking for an exit. The 63% rule allows the spent gases to escape. but......and a big but.....leaves the heat that is created in this process to stay in the oven creating the "mass" of heat needed to penerate the dome walls.

This is why the true Pompeii always has it's vent on the outside of the dome.

By having your flue coming out of the bottom rear of the oven, can have no significant purpose to how these ovens work......that is only my opinion.

Many modular ovens that come from the continent have the vent at the top or the rear top of the dome. Most are fitted with dampers to prevent heat loss, but I believe this is more of an ease in producing these modular ovens, than design.

.....all the rest of your design sounds.....spot on.

Terry

[faz]

The only way you'll get any of the exhaust gases out of a chimney located that low in the dome is if you have some sort of fan or ejector system in the stack, which will force gases out of the rear of the furnace. You'll still have to overcome the hot gases tendency to rise to the top of the oven andto be honest I can not see that it would work for a pizza oven.

I built my pompeii using storage heater bricks and it has had quite a few hard firings now. The bricks all seem to be in good condition and there does not seem to be any deterioration in them at all.

[bookemdanno]

Hmm, yes, i think the Chimney/exhaust would become the intake for cooler air into the fire and all the smoke/heat would simply exit out the front.

What about basing the design more closely upon a traditional pompeii style dome, but creating a flat profiled flue/chimney which will flow backwards over the dome bricks, maybe over the ceramic blanket, but held within an increased depth Vermicrete layer. A metal fabricator would be able to create a steel section which could follow the radius of the brick dome relatively easily, and a manifold section to connect to a brickwork vent, i'd say.
Thus creating the clean lines you seem to want, but staying closer to the tried and trusted route? The Flue/chimney willl benefit from the insulation, creating a good draw.

Hello, and welcome by the way.
I like the fact that your challenging the design, this is how progress occurs!

[spinal]

Welcome to the forum

As if the other's haven't been mean enough, I'll throw in my tuppence

If the pink is vermicrete (vermiculite/OP cement) I think you'll find that being exposed to the hot face directly will cause the portland cement to break down (600c IIRC), which in turn will make the vermicrete loose structural stability. You could like it with fire bricks on the inside first? (or was that your plan and I'm just too thick to get it?)

Also - if you plan on cooking without a fire (i.e. on retained heat) you'll have trouble keeping the heat in the oven with a door that big...

Just my opinions of course

[tonyb]

Hi and welcome.

Like the others I don't think the design of your oven will work very well. Air/smoke/fire take paths of least resistance so I suspect the smoke out would still beat the front despite the flue at the back which I don't think will work without some form of forced extraction and even then will lead to very low efficiency.

I think you can take it as read that if there are no existing wfos with is design or historical reference designs then its not a good idea.

Back to the Sketchup drawing board I'm afraid.

[Fat Bob]

I am with Bookemdanno the flue will become the air intake and all the heat will rush out the front.

Sorry it is a no go idea.

[turkey]

hello there, when I read the description and saw the rear elevation I assumed you where making an oven in the shape of a pill capsule, but it seems you wish to leave the front open like a cross section?

Bar tradition and such the rear flue may be hard to get to work, heat will rise and the front has a much higher exit point so the hot gasses are likely to leave this way. This is both good as the heat will pass over all the structure heating it but also bad as 1 thats not your design, 2 it will be really at eye height (and you dont want hot gas / smoke in you face) and 3 there is no flue or other device there to accelerate the gasses and cause a draw effect.

If you closed the fron section down or had a full height door and set the fire near the rear you might be able to make the rear flue draw and have the fire burn nicely, but then you will not get the gasses passing over the brickwork so will have to rely on radiant and IR heat rather than convection. It will still get hot it would just take longer, and even with ideal conditions because of how dense the bricks are it already takes a fair while to heat.

if you dont want the flue at the front some folk do make an external flue travel out the front and then back over the top of the dome to a stack at the rear so the gasses are released well away from the user. The initial idea was to do with heating the dome with the flue gases on this revers pass, although I am not sure how effective this is, it is used and it not totally out there.

mha-net.org/docs/v8n2/wildac06b.htm

there is a good example of what I was trying to explain.

I suppose what I am trying to say is what part of the normal design do you not like, and what would you like to achieve with your oven, and we may be able to offer some advice or point you in the direction of builds we have seen that might help. The traditional ovens are a tried and tested design, I am sure you can alter them somewhat and we are not historians so more than happy to try and assist with out of the box ideas, but there is probably a reason the ovens where not historically improved upon, they work as is

[danmarley85]

Thanks for the imput guys, as said previously, I'm here to learn!

I think my sketch-up may have confused the issue however, I would build the oven with a door/entrance smaller than the vault size (as is the norm) and not open across the front.

I've not added this on to the sketch up drawing to keep it simple in this early stage (epic fail perhaps). Sorry if this has lead to confusion.

From what I understand if I have the flue at the rear but higher than the top of the door the design would work?

Many Thanks

[cannyfradock]

Hey Dan

Hope you didn't get put off from our negative vibes on your original idea.......we love new idea's.

As I mentioned before many continental ovens have the vent at the top and rear of the oven. The better ovens with this set up always have a damper system to close of the chimney to enable the user to save heat and make the oven more economical to use.

This is another take on achieving the same goal, and sounds very interesting.....please keep us informed on your build progress.

Terry

[turkey]

I believe what you describe is a squirrel tail oven and is a known design so perhaps you might need to research those and how well they fire, there are even a few historic examples lurking in the UK as far as I know :-)

[DuncanM]

I think one negative having the exhaust at the rear of the oven is that it won't be coming back over the food you are cooking (e.g. pizza), nor would it heat the top of the dome. I'm not sure how much this would affect the heating of the oven but I'd expect it to take longer to heat up, be less efficient and take longer to cook things.

That being said, it's your oven and you build it how you want it These are observations, if you don't mind the negative aspects of the design then go for it.

If you wanted the chimney at the rear of the oven - but wanted to take advantage of the extra heat in the exhaust gasses you could as Turkey suggests - have the entrance to the chimney at the front, but using some chimney ducting fold it back on it's self to the rear of the oven where a chimney stack would be.

I'll follow your build with interest!

[jonnycj]

Just my penn'orth, but you say that you don't like the flue at the front - I take it that this is just for aesthetics ? If so, I would flick a little switch in your mind to "I do like the flue at the front " !

Having gone through the whole new build/design etc etc. I found that the tried and tested methods that have been used for centuries work best and trying to re-invent the wheel will end up with poor performance and issues when you come to use the thing.

The 63% ratio imho is vital to getting a good draw through the oven and that's vital for getting a good burn, which is vital for a quick heat up, which is vital for cooking !

You can try things differently, but the amount of hours working it out in your head, designing and then building will all go to waste if you don't actually use it because it's not really doing it's job properly.

Fatima Whitbread was no Kate Moss, but she couldn't half lob a discus !

Despite the weather this summer I've had loads of enjoyment out of my WFO (see Wirral WFO) and had it not worked properly it would have been significantly less enjoyable, significantly less used...you get the picture.

Were we building something completely new and without a tried and tested design, I'd say go for it, but these things have been around for probably 1000 yrs plus and they'll have had time to iron out any design flaws.

I certainly don't want to be a killjoy, as I'm all for tweaking and modifying, but when it comes to something that you'll really enjoy if you get it right and loathe if you don't, I'd be tempted to flick that switch.

Cheers

Jonny