What are the consequences of building your dome too high?

[Santino]

I built my dome without the use of any forms - just a piece of plywood that I used as a guide all the way up. I wasn't aggressive enough at following the curve from the beginning and by the time I got halfway up the dome, I knew I'd be too high. I ended up 3" too high (needed 18" and finished at 21"). Does this just make my dome less efficient or am I looking at seeing other problems as well?

[GianniFocaccia]

Your oven is neither less efficient nor problematic as a result of the finished height of the dome. Essentially, it is what it is.

A recent study of dome radiation by mklingles suggested that the heat pattern from a 21"h dome compared to an 18"h dome was virtually identical.

http://www.fornobravo.com/forum/f9/m...try-15292.html (Mathematical analysis of dome geometry)

I think the most interesting thing I've learned is that the intensity is a bit more then double at the edges of the oven. Also in a 42" oven there's a good 20" middle section with nearly uniform radiation, but beyond that the intensity starts to increase quickly. Also here you clearly see that 18" vs 21" height didn't make much difference.

Also, don't forget the vast history of beehive ovens that worked their magic for many, many years.

[Santino]

Cool post...makes me feel better!

[Neil2]

Your opening should still be 63% of your finished dome height.

For your dome height the opening should be 13 1/4 inches. If it is less than that you will get more incomplete combustion, more smoke and greatly reduced efficiency.

[Santino]

Well thanks a lot Neill for bursting my bubble! Oh, well - you live and you learn. Hopefully it will be ok because my arch height is definitely 12".

[SCChris]

Santino, throw a 3cm layer of Soapstone on the floor, voila!

Chris

[mrchipster]

Originally Posted by SCChris

Santino, throw a 3cm layer of Soapstone on the floor, voila!

Chris

Wouldn't that just make the inner arch opening smaller and make the ratio worse?

Chip

[SCChris]

Hmmm, I guess I didn't think that one out quite right.. Now if you could add the SS to the roof of the oven that would do it.

Chris

[Hank10746]

As I understand the difference it is between Higher being better for bread or Lower being better for Pizza. If that is the case in your oven then you could as Chris said put in a layer that would
take up the extra space but since you are making Pizza you would only use enough to cook Pizza on. You could then if you are getting smoke like Neil2 said use a small fan to add the extra air needed to get complete combustion. It would be best if it were a controllable exhaust fan as you would be drawing the air in as fast as you are exhausting it. Pushing air might be more of a problem than you have now. Think about a forge or a horseshoer working on a horseshoe they push air in faster than would be normally used . I think it might be called a blast furnace. By adjusting the air flow you should be able to overcome the small opening. I also think I remember seeing a post that said somewhere between 60% and 65% was fine 60% would be 12.6" might make you feel better.

[SCChris]

Ok so I may be branded a blasfemer, but has anyone seen any combustion science relating to entry height / dome height ratios relate to combustion?

I know that the 60% to 65% is the sacred mantra here, but I haven’t seen any evidence.

Is this ratio just our "urban legend"?

I’m sure that air / exhaust flows can be modeled. I remember seeing a model a couple of years ago of this on this site that showed the heating of the oven over time.

It would be interesting to see the science and how various door height ratios, door widths and opening shapes relate to combustion.. BTW my opening is at the standard 60-65%.

Chris