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Old 09-10-2011, 03:39 PM
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Default Re: thermal mass ratio hearth:dome

I built an oven with the dome bricks sideways (2.5") for a uniform brick thickness. It works fine, except for a lot of cracking, which is not a problem, except right around the door opening, which I have had to patch, and will again.

The 4.5 inch dome thickness is a lot more stable. As for the thickness of the floor, the matching 4.5 inch thickness is overkill, and hard to heat to pizza temperatures, although the additional thermal mass may be useful if your main goal is to bake repeated batches of bread on a single firing.
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Old 09-11-2011, 03:29 AM
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Default Re: thermal mass ratio hearth:dome

Quote:
Originally Posted by GianniFocaccia View Post
My plans are to make pizzas on friday evenings, bread and roasts on saturdays and slow-cooked dutch-oven dishes on sundays, but who knows? The oven's coast curve won't be observable until I get it finished!
John
Thanks for the reply John,
This is what I am aiming for myself, as soon as my second round of curing fires are over (had to repair huge crack) I'll be getting some good data to share.
Thanks
John
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Old 10-01-2011, 03:11 PM
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Default Re: thermal mass ratio hearth:dome

Well, I cranked out 12 12" pies in 35 minutes on Thursday evening as my oven nears the end of curing/drying out. For the purposes of this thread I choose to build a very well insulated ~6" dome and ~6" hearth as I'm actually more into bread than pizza. The interior shape and design in general is very close to the 36" Pompeii except in addition to the extra thermal mass I have a clay dome with one course of firebricks on edge to protect from tool and fuel damage. It's still a little early to draw conclusions other than it's awesome! It's cooling off faster than I expected but I attribute that to curing.

I'm having problems with the hearth temperature exceeding the dome for baking bread which I expect is from two different sources: 1) I've been a little too casual with fuel wood selection and preparation. Some of the wood I've used has been too large or not dry enough with less bright fires. 2) The dome is still pushing moisture out of the insulation layer. Should do better when it's fully dry. I also can have this problem during cooking pizza when I don't have a good bright fire.

I hope to post some thermal performance conclusions and photos in a couple of months.
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Old 03-04-2012, 04:16 PM
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Default Re: thermal mass ratio hearth:dome

Well after quite a bit of [TOTALLY AWESOME] use, I can report that although my oven has some issues it performs very well. As I stated in previous posts, my dome and hearth are ~6" and in terms of thermal performance I can report the following:

1. This amount of thermal mass takes a lot of fire over a long time to saturate the whole thing. I don't have exact data but getting to triple load bread baking temperature I usually fire the oven to pizza temperature followed by pizza of course. If the oven started cold I fire a bit more after pizza. The next morning I make a wild guess about how much fire will bring my dough and temp together at a reasonable time in the afternoon.

2. For bread I find when the outside of the mass reads ~400F and the inside is ~500-550F I can bake 18kg of dough in three loads very nicely, with the final temperature ~400F and rising. It's possible I could do more with a rest in between, but I haven't tried that yet. Sorry to mix Imperial and Metric, but I simply can't imagine doing bakers math in Imperial units.

3. As I noted in prior posts the hearth seems to be a little hotter than the dome for bread. It is less of an issue than it was initially, but I still get more color on the bottom. I'm still not certain of the reasons, but if I felt it was a big enough problem to address I would look into the thermal characteristics of the sand/clay dome versus the fire brick hearth or even less likely the height of the dome.

Quote:
Originally Posted by dmun View Post
The 4.5 inch dome thickness is a lot more stable. As for the thickness of the floor, the matching 4.5 inch thickness is overkill, and hard to heat to pizza temperatures, although the additional thermal mass may be useful if your main goal is to bake repeated batches of bread on a single firing.
4. While intuitively I want to agree with this, in practice, for the rather small amount of pies I tend to make at a time (<20), even from a cold start the hearth heat doesn't *saturate away* fast enough to make a big difference. If I start in the upper 700s, it will still be over 650 by the time I'm done. If I was planning on making a lot of pizza I would of course have to preheat or switch around my live fire and cooking space, or some such.
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