Vent & Chimney design

[pizzahead]

Hi. I have decided on a 1000mm oven. I have constructed the base etc and have the materials ready to start the dome very soon. I am wondering about the design of the vent and chimney. I have attached my current design and would appreciate anyone out there having a look and giving me some feedback on it. I plan to make the height of the dome between 400mm to 500mm (17"-20"), opening is 480mmx290mm (20"x12").

My main concern is that it will not draw well. Chimney opening is 360mmx115mm (15"x5").

I have not yet decided on chimney style or height at this stage.

Regards,
Jason

[nissanneill]

Hi Jason,
I would make your vent at least double the size. The width is OK but only 115mm deep , I don't think will handle the smoke and it will spill out the front and stain your face bricks
Make your void one and a half bricks rather than a single brick which will double your area to collect and funnel the smoke/gasses up your yet to be decided chimney.
Check out my void which is much bigger and works a treat at:

http://www.fornobravo.com/forum/f8/n...-1-a-2005.html

It is a 40"Pompeii complete build, just follow the prompts.

Neill

[pizzahead]

Thanks for your prompt reply Neill.

Do you mean like the attached?

Cheers
Jase

[nissanneill]

Exactly Jase.
It will be twice the area and closer I believe to what will be needed. It will be 0.028 square metre when your original one was only 0.01414 square metres in area.
My vent is relatively large being 600mm wide X 390mm deep, (0.234 square metres in area) funnelling the smoke and gasses into an 8" flue.
It is best to have a little caution now than to wish that you had done it initially.
I am making a similar unit for Paul Henderson's Pompeii which will be 490mm wide X 245mm deep(which is a less but that is already bricked up and I will have a deep funnelling action to reduce any smoke exiting the front archway only 0.12 square metres in area). Much less area but as it is already bricked up I need to make it deep funnelled to reduce any smoke exiting the front arch.
I just need to get my backside going to complete it ASAP.
I have attached a picture of my stainless chimney

Neill

[pizzahead]

Neill. Thanks again. Am I correct in assuming that you cannot have a vent that is too large? I couldn't agree with you more that I need to get this right now rather than construct it and then wish I had done something different.

I Have change the design again to have a vent opening of 580mmx230mm which woudl give me 0.13m2 area (see attached). Looks like you got your chimney and vent fabricated to fit your sized opening.

Cheers
Jase

[nissanneill]

There is a posting somewhere here in the forum that calculates the efficiency and flow factor for chimneys. With my measurements, it comes in very high up the scale and draws exceptionally well.
Your draft #3 is even better (0.1334 square metres), than your other 2 and I would be happy with these figures in a new oven that I was to build.
The only problem with a larger void is having to reach a little further into to oven but that is a small price to pay for the benefits of a larger smoke free entrance/void.
Check out:

http://www.fornobravo.com/forum/f28/...ator-3905.html (chimney flow rate calculator)

there are a host of comments on this topic.
I hope this helps.

Cheers,

Neill

[pizzahead]

Thanks again. What did you use for a chimney?
Cheers
Jase

[nissanneill]

I had a spare length of 8" slow combustion stove flue and purchased 2 more. They just push together and sit in a snug hole cut into my stainless 'funnel and rise 10' high.
I might put in a couple of bends in the chimney so as to by pass the new patio roof rather than run it through it. Final decision yet to be made.

Neill