Pompeii Oven Vent Opening. Big mistake?

[briram]

Hi all,

I am new here and hope to get some guidance. I am building an a 36 inch Pompeii oven and I am following the Forno Bravo instruction. It is recommended to have a chimney of diameter 6 inch. So I took a piece of pipe as orientation while building the outer arch. As I started building the inner arch I've realised that the opening might be too small for the smoke to escape. I think diameter 6 inch applies to the final opening but I think the first opening for the smoke to escape should be much wider.

What do you think? Should I carry on or make some corrections before.

Thanks in advance

[briram]

I should have posted this into https://community.fornobravo.com/for...n-construction
Could an admin please move this to the other section? Thanks a lot

[UtahBeehiver]

The area opening in the vent chamber should be the same or more the the area on the ID of the chimney, IE the chimney ID area is pi X radius square (3.14 x 3 x 3 = 28.26 sq inches. So remember you will have a mounting plate for you chimney stack which sits on top of the arch. Square opening is not quite as effecient as a round opening but you are in the ball park when you factor in the OD of the chimney sits inside you vent opening. DavidS takes a little a a venturi effect when the vent opening is smaller than the chimney opening but I will let him address this.,

[briram]

Thanks for your quick reply. I still don't have a mounting place. I was thinking about taking a round one and build around it. By the way I am building the oven in Frankfurt Germany.

Do you suggest that dimension of opening is only relevant for mounting the chimney? I have concerns that the smoke will not be able to escape through this narrow opening that is about 15cm x 15cm (6" x 6") and instead will reach the outter arch.

[UtahBeehiver]

6 by 6 is 36 square inches exceeding the area of the ID of the chimney so you are good that way. You can round the inside of the edges of the bottom part of the vent bricks to aid in the flow.

[briram]

yes, I checked again, it is exactly 6"x6" and as it seems I will round the inside of the edges...I hope it is enough for the smoke to escape.
After rechecking the Manuel again it said "you can either leave a roughly 6"x10" opening for use with a rectangular refractory chimney flue liner, or a 9 1/2" opening for an 8" Simpson DuraTech Anchor Plate" I should have done my homework earlier. Now I have 2 choices, going with I have now or cut parts of the previously marked stones so that the opening is wider. The second alternative is an open heart surgery and I fear the vibration during the cutting will damage the outer arch...

[UtahBeehiver]

6" ID chimney will work for a 36" so you are good as is. 8" is for larger ovens.