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-   -   Chimney and Vent Transition measurements that count (http://www.fornobravo.com/forum/f9/chimney-vent-transition-measurements-count-8797.html)

dinoforno 11-12-2009 11:09 AM

Chimney and Vent Transition measurements that count
 
Folks,

Been working on this with my dad. Either I am going crazy or he is making me crazy. He has built a ton of chimney for fireplaces and not many pizza ovens lets just say that.

My door height is roughly 15.5 in tall and 17 in wide. When it comes to the Vent and Chimney transiton what is the right combination of Vent Size both width and depth to a 8" clay chimney flue. My dad insists that between door of the oven and the outside of the oven which I am calling the depth should more than 8.5 in....yet I see no mention of this concern on this site.
As well as the front of the oven where the vent sits on a brick everyone's design seems to show a straight shot from the vent arch to the outside part of the oven with no block to create a chamber. Does the smoke come out of the front ? If there was to be a chamber area how big should that be. Father insists on it being 4-5 in or roughly 1 in down from the door opening.

I am stating to get frustarted with finishing this thing before the holidays and just wait until spring but I figure some sanity from folks here might set me straight. As i was about to buy two flues and build a vent like one that Dnum did in his geodisc design but now I got my maestro telling me the depth is to small.

What is right or can someone say what worked best for them so I do not feel like I am going about this the wrong way.

Dino
"torn do you listne to the maestro with the experience or do you work out the math and research that you have done?"

dmun 11-12-2009 12:36 PM

Re: Chimney and Vent Transition measurements that count
 
Quote:

My door height is roughly 15.5 in tall and 17 in wide. When it comes to the Vent and Chimney transiton what is the right combination of Vent Size both width and depth to a 8" clay chimney flue.
If you can flare out your flue at the entry to about twice it's internal size, to form a funnel, you'll get better draft.
Quote:

the front of the oven where the vent sits on a brick everyone's design seems to show a straight shot from the vent arch to the outside part of the oven with no block to create a chamber. Does the smoke come out of the front ?
This depends on your flue. If it's big enough and tall enough, only a whiff of smoke will come out the front. I don't think there is any advantage in building the external opening lower, although some builders have done this. It means you have to tilt the door to get it it.
Quote:

i was about to buy two flues and build a vent like one that Dnum did in his geodisc design
The depth isn't particularly important. My oven didn't have enough room in front, and the back part of my flue tile is built out over the top of the dome. Works fine, but of course I have a REALLY tall chimney.

dinoforno 11-12-2009 01:05 PM

Re: Chimney and Vent Transition measurements that count
 
Thank you sir!

That is helpful but when you say flare out to about twice its internal size. Do you mean from the door length or do you mean outward from the door. I understand how you would not have had room because of where you built it but the question that is boggling me right now is the vent funnel approach should it be done not only on the side of the chimney but on the back side as well to come out a bit. If so I am going to take your flue approach and add more of an angle on the side that is over the door. That is the only thing I can think of doing giving me roughly a a slant on the sides and on the back closests to the oven. This should make my vent roughly larger than the 8.5 in opening of the flue that I put together with the cement. I am going to try and draw this out or sketch it up as I am not sure I am even making sense anymore.

cannyfradock 11-12-2009 01:54 PM

Re: Chimney and Vent Transition measurements that count
 
1 Attachment(s)
Dinoforno

Makes perfect sense to me. When I built mine,(in summer 09) I did'nt realise free plans were available on line, so everything was built on views of pictures and guesstimation. My only concern was the positioning of chimney in the arched opening. My arch is 2 bricks in depth and i created the outlet at the back of the first brick. Perhaps you can see from the link, where I put the chimney opening.

Picasa Web Albums - lyons-t

I've only fired mine up once and at the start a little smoke came out of the front, but once the wood-oven started working the smoke started drawing up the chimney (must lenthen my chimney to improve draw).

Shall be following your thread with interest

All the best on your project.

Terry (C.F)

dmun 11-13-2009 07:07 AM

Re: Chimney and Vent Transition measurements that count
 
Yeah, I'm confused by your last posting.

This is what I did: The flue funnel is twice as big at the bottom as at the top, and the same depth. Works fine. This is not to say it's the only way of doing it, it's just what I did.

http://www.fornobravo.com/forum/phot...n_vent_008.jpg

dinoforno 11-13-2009 07:15 AM

Re: Chimney and Vent Transition measurements that count
 
OK

Thanks I understood the flare out to the sides. It was the flare out from the oven that I thought you were refereing to....I am working on flaring out from the oven a bit. To make my dad happy and to create a perceived larger opening going from front to back. I will just cut the brick so that they have more of a slant leadnig into the flue. I took your idea with the slue and used it already. Thanks for that. This is what got me thinking in the first place with what my dad was saying around the chamber for the front and having some space from front to back more than 8.5 inches. I did my design in Autocad last night in 2D fighting with it in 3D to just get a picture in my head and dad. Talking and drawing in 2D does not really do it justice and leads to a lot of discussions with a 80 yr old wise man.

Neil2 11-13-2009 10:58 AM

Re: Chimney and Vent Transition measurements that count
 
I view the purpose of the vent to deflect hot gasses and smoke upward away from the cook's face while cooking.

I am not concerned with the smoke and flames licking out the front while firing.

nissanneill 11-14-2009 01:28 AM

Re: Chimney and Vent Transition measurements that count
 
1 Attachment(s)
dinoforno
My 40" Pompeii emits no smoke out of the front because the void in front of the oven measures 24" x 16" running up to an 8" flue which is 10 feet high.
The bricks on the dome oven arch are beveled to help the smoke direct itself upwards and gather speed to funnel into the flue.
I am very pleased with the performance and only get some smoke out the front arch when I excite the fire with a petrol leaf blower which turns an ailing fire to a roaring one in less than a minute (partly due to unsuitable wood being burned).
You can view all of my build to check out the mentioned beveled bricks.

Neill

jmhepworth 11-14-2009 04:50 AM

Re: Chimney and Vent Transition measurements that count
 
Of the many things I would do differently, enlarging the funnel above the vent would be one. I get some smoke out the front of my oven during start up, particularly if the wood isn't completely dry. I would like a larger area to allow more smoke to gather before it goes up the chimney. I also used 8 inch clay chimney tile, and I'm starting to wonder if that was big enough for a 42 inch oven (the inside measurement is 6 inches). The chimney draws great when the oven is roaring, but it looks like I will get smoke staining on the front, which I had hoped to avoid.

nissanneill 11-15-2009 02:37 AM

Re: Chimney and Vent Transition measurements that count
 
Joe,
I agree whole heartedly, that is why I have adopted the signature on my postings. Do it right the first time and you really do have no worries! Just finding out or believing a variety of replies to a question sometimes causes confusion.
Apart from that, I hate having to undo a well built product to make the necessary changes. Ovens with smoke stained fronts to me look inferior.


Neill


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