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130mountainside 04-26-2010 02:26 PM

Dimensions
 
How critical is it that the entry height ratio be 65% of the dome height? I am at a stage where I can make some adjsutments before...the project is in cement. I have a
32" diameter, 17" width, 12" entry height. I planned on a 16" high dome. That puts the ratio at 75%. I could always reduce opening height by puttimg 1-2" of mortar on the underside of the arch.(already installed- to avoid ripping it out)

Your comments would be appreciated.

Thanks,

Patrick

Neil2 04-26-2010 05:03 PM

Re: Dimensions
 
In my opinion, the 63% ratio is critical. This ratio allows the burning hot gasses to circulate in the dome long enough to give up their heat before exiting the opening. A higher ratio (75%) means that you will have to burn more wood - maybe a lot more wood.

RTflorida 04-26-2010 09:11 PM

Re: Dimensions
 
I agree with Neil, 63% is considered ideal; but anything between 60-65% is acceptable. 75% is really pushing it, it may act more like a fireplace than an oven with that large an opening.

RT

Tscarborough 04-26-2010 09:15 PM

Re: Dimensions
 
I wasn't so much skeptical about the ratio as I was ignorant, but I must say that that nugget of knowledge alone made my oven work. I would hazard a guess that it just about the most important design specification of the entire project.

130mountainside 04-27-2010 05:45 AM

Re: Dimensions
 
Thanks for the clarification.

GianniFocaccia 04-27-2010 06:36 AM

Re: Dimensions
 
Ever consider adding a second arch of 2" bricks under the existing arch? Sure, it's a lot of work, but the result would render an effective fix and appear to part of the original design.

130mountainside 04-27-2010 07:11 AM

Re: Dimensions
 
Thanks, good idea. I was thinking of just that- but cutting brick into crescent moon shapes and cementing them in to have a flat surface vs an arch. It won't be that visible anyway.

Neil2 05-04-2010 01:53 PM

Re: Dimensions
 
You just need to lower the high part of the arch down a couple of inches not the whole width of the arch of course. Hunt around for a scrap of sheet metal or bar or angle iron the right size. If you do it at the inside of the arch it will soon get black with soot and won't be visible.

Food With Legs 05-06-2010 08:07 AM

Re: Dimensions
 
How does the shape of the oven opening (arch top versus straight across) affect performance/wood consumption? It seems that if it matters at the very point in the centre of the opening it would matter all the way across, right? Or is this just one of those questions that is unanswerable because no one has two exactly the same ovens that differ only with this variable? (Or I suppose an advanced thermodynamics simulator.)

Quote:

Originally Posted by Tscarborough (Post 88306)
I wasn't so much skeptical about the ratio as I was ignorant, but I must say that that nugget of knowledge alone made my oven work. I would hazard a guess that it just about the most important design specification of the entire project.


Tscarborough 05-06-2010 08:32 AM

Re: Dimensions
 
I would think that there are 2 factors at play:

1. The overall square inches of the opening.

As an example the rule of thumb for fireplace opening to flue size is 10%. I used this to figure my oven flue size: door opening=325SqIn, Flue=36SqIn.

2. The differential between the dome height and the door height.

So far as I can tell by watching the smoke during startup, the differential creates a roll of smoke that assists with the draw, similar to the way a smoke shelf helps a fireplace. I would also assume that it allows more heat to be trapped in the oven after initial warmup.


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