#1  
Old 06-06-2011, 04:36 PM
Serf
 
Join Date: Jun 2011
Location: Simi Valley,Ca
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Default Pompeii Oven shape

Have been lurking for awhile! Need some advice about oven shape.
Originally was going to do a cob oven so had built a foundation in a corner.After doing further research am now leaning toward the Pompeii.Trouble is, the foundation maybe slightly too small now! It is a 59" long wedge with the small side rounded like an orange quartered<).
The long edges are at 90 degrees.By my measurements, I wont have room for the landing and much of a vent.Is it possible to go with a slight elliptical shape rather than perfecly round to accomidate the vent and landing?I was trying to preserve as much oven size as possible.could just go for a smaller oven.Any suggestions?
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  #2  
Old 06-07-2011, 05:59 PM
BriggsARNP's Avatar
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Join Date: Apr 2011
Location: Pasco Wa
Posts: 57
Default Re: Pompeii Oven shape

I am not sure that I can visualize your stand. If it is too short I have seen quite a few builds on here that cantilever the front of the hearth using reinforced concrete. I am sure that you could pick up a few extra inches that way.
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Old 06-07-2011, 09:48 PM
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Join Date: Jun 2011
Location: Simi Valley,Ca
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Default Re: Pompeii Oven shape

The foundation is basically triangle exept one side is slightly rounded.somewhat but not exactly like this <).
Do you mean a shelf type cantelever? Or repour the top? I was thinking of repouring the insulating layer with a stone shelf inbedded in the front to cantelever the additional inches.
You are suggesting to repour the concrete top with a cantelever framed in?

Is the elliptical shape a bad idea?

Thank you for your reply.
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Old 06-07-2011, 10:38 PM
BriggsARNP's Avatar
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Default Re: Pompeii Oven shape

OK. Disclaimer time. I have not yet built an oven. My opinion is based exclusively on what I have read and seen on this forum. That being said, I think that the round shape offers better heat distribution to avoid hot spots and cold spots. It also works to make a stronger dome. I am not sure how an ellipse would hold up. From what I have read doing the round dome it makes the oven basically self supporting. I know that there are several folks here who have barrel vault ovens and they make amazing wonderful food so my opinion that spherical is better might be based upon faulty logic.
If you go through the following thread I believe you will find some examples of the cantilevered "counter" in front of the over. If the link doesn't work because I am but a lowly peasant then you can find it in the newbie forum.
http://www.fornobravo.com/forum/f2/n...res-15133.html (A newbies survey of the Forno Bravo treasures hiding in the archives)
Dino does it that way and I believe that My Old Kentucky dome does it that way. I would definitely wait for others to respond before taking my opinion as the only way to go.
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Old 06-08-2011, 02:29 AM
david s's Avatar
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Location: Townsville, Nth Queensland,Australia
Posts: 4,724
Default Re: Pompeii Oven shape

The hemisphere is the best combustion chamber and also the best form for reradiating heat back, but if you deviate a little and go elliptical it won't make any measurable difference. I t will however, be more difficult to build instead of using an indispensable tool you might be better off building a sand castle and bricking over it. A cantilevered slab might be an easier solution, or perhaps a little of both.
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Old 06-08-2011, 07:51 PM
Cheesehead's Avatar
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Location: Western Wisconsin
Posts: 42
Default Re: Pompeii Oven shape

Barbara,

See the Pompeii plans. If you haven't gotten them, you can "order" them from the store - they're free. There are diagrams for corner builds. Mine is 63" with a corner cut off, and I can get a 38" diameter interior oven fitted.
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Old 06-08-2011, 08:01 PM
Journeyman
 
Join Date: May 2009
Location: Detroit
Posts: 397
Default Re: Pompeii Oven shape

Boy old fallacies die hard around here.

The hemisphere is NOT some magic shape for combustion. Even Hemi's don't have hemispherical heads anymore because other shapes are more efficient. Even when the hemi was king, it was due to valves size and airflow, not the hemispherical shape. Shape has no effect on the ovens combustion unless it is so radical it has drastic effects on airflow. As a guy who works with airflow on a daily basis I can tell you a a lower flatter dome is not going to effect airflow to the point of decreased combustion efficiency.

As for radiation, the bricks in our ovens are not perfect emitters, not even close. What we get is diffused radiation like the sun on a cloudy day. On top of that even IF our ovens did radiated in a perfect textbook way the hemisphere would not be better because of it. It would focus all it's heat on the center of the oven and you would have a hot spot in the middle gradually getting cooler towards the outside. A low dome oven on the other hand would focus it's heat over and much larger area of the oven floor, and therefore would be much more even. There are images I made to display this floating around in a thread last times these fallacies where thrown around as fact.

Build the oven the shape that suit's you, hemisphere if you want easier to build or room for larger items and a lower flatter dome if you are willing to make trade offs for the ultimate pizza oven. Both have their ups and downs and neither is right or wrong.
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Old 06-08-2011, 10:40 PM
Serf
 
Join Date: Jun 2011
Location: Simi Valley,Ca
Posts: 4
Default Re: Pompeii Oven shape

So nice to see so many replies and all are so good..
I did look at Hansen build,btw what a beauty! I see what you mean Briggs about the cantilever.Just to clarify,was thinking about elliptical or oval for the base shape and not so much for the actual shape of the dome.Although after a search and reading through threads,has me thinking about the arguements on both sides for low vs high domes and round vs oval footprints.I have to say being able to use the indespensable tool to build the dome is extremely appealing to an absolute amateur such as I, so the difficulty in building an ellipse or oval...Has anyone built an oval or ellipse footprint from brick?
Now about the hearth base.the foundation is stacked mortared rock wall backfilled with urbanite, gravel and sand and floated with an insulation layer a la Kiko Denser.Do I need to repour a hearth base with cantelever and then another insulation layer, or can I mortar a precast piece or stone cantelevered shelf near the front and pour an insulation layer around this? The vent area and landing would not be insulated as a result, but it would be less work in my mind.any other suggestions highly appreciated.Would be a joy to get away with a bigger oven.
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  #9  
Old 06-09-2011, 12:21 AM
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Default Re: Pompeii Oven shape

Barbara hit return now and then, its make for easier reading rather than one big block of text.
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  #10  
Old 06-09-2011, 12:59 AM
david s's Avatar
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Default Re: Pompeii Oven shape

[QUOTE=shuboyje;

"The hemisphere is NOT some magic shape for combustion."

Thanks for the illumination Shuboyje. My experience with kilns and ovens in the form of a cube, with their problems of poorer circulation and cool spots, has led me to believe that the closer you get to the hemisphere the better the improvement. But I stand corrected, as you obviously have expertise in this field.
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