#11  
Old 04-14-2009, 11:16 AM
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Default Re: Hearth Floor

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Originally Posted by james View Post
You can just fire your oven longer with the standard floor, and you will never completely "fill it up".

James - isn't there a point where the bricks get saturated? I know I've seen where I slid out a dutch oven that the bricks under it were cooler. It just seems adding a "little" more mass might not be a bad thing. Wasn't someone building their floor with the bricks on edge - be interesting to see his numbers.

les...
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  #12  
Old 04-14-2009, 11:42 AM
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Default Re: Hearth Floor

Hi Les,

They will definitely eventually get saturated, but I think it's at a much hotter and longer burn than we are typically doing when we either bake pizza or fire our ovens for baking. I used the term "never" too liberally -- but my point is that we aren't "filling" the floors that we have. I have never even fully fired a Primavera -- which holds a huge amount of heat.

In terms of floor mass, we've seen it all:

9" Scott oven -- bricks on side, set on 4 1/2" concrete slab
5" 2" Casa floor set on 3" firebrick island
4 1/2" bricks on side
2 1/2" - 3" firebrick floor
2 3/4" Modena commercial oven floor
2" precast residential floor
1 1/2" firebrick split floor

James
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Old 04-14-2009, 12:03 PM
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Default Re: Hearth Floor

MK1,

Check out this thread.
http://www.fornobravo.com/forum/f17/...temp-6528.html (consistent hearth temp)
It discusses the problem of burned bottoms on bread. I think a cooler floor is acutally a benefit when baking. I do a lot of baking (see this thread) - (32 lbs of bread) and have had more problems with burnt bread bottoms than anything else. I think of the dome as the battery that charges the oven. A little extra mass in the dome (I added 1inch of mortar) may help, but others without that extra mass have reported very similar oven temps over time. I think the real key is insulation.

Hope that helps,
Drake
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Old 04-14-2009, 01:56 PM
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Default Re: Hearth Floor

Thanks to all for the replies. I have a clearer picture of what's happening in the oven. The thread Drake refers to is somewhat telling in that each quadrant has a slightly different temp, particularly the fire quadrant.
I'm assuming that when James says we're not filling the floors as it is, the dome is 1000F near the end of firing, the floor is somewhere below that (800?) and as the initial "plasma" phase dies out the respective temps equalize.
I have my four piers done and in the next few days I'll pour the slab. I'm going to insert an .015 X 3" stainless flashing edgewise into the concrete (vertically) that will describe the outer perimeter of the insulation and be inside the final render (igloo design) I'll soon post a few pictures as there is more to look at. I will also mention that I've looked at almost all the builds on this forum and you SOBs have set the bar pretty high!

Mark
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Old 04-14-2009, 02:22 PM
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Default Re: Hearth Floor

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I know I'm being a PIA but I am compelled to turn this thing over in my mind until I think I understand the thermal dynamics of the oven,
Not at all. We would a LOT rather have people ask questions before they build, rather than after.
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always trying to reinvent the wheel.
I'm in no position to criticize any one for that.
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Old 04-14-2009, 02:38 PM
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Default Re: Hearth Floor

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Originally Posted by MK1 View Post
I'm assuming that when James says we're not filling the floors as it is, the dome is 1000F near the end of firing, the floor is somewhere below that (800?) and as the initial "plasma" phase dies out the respective temps equalize.
Mark
Mark, that's not quite it. Typically you can fire the dome and floor to roughly the same temperature.

Think if the floor (or dome for that matter) as having both inner and outer facing edges. When the inside of your oven is hot, let's say 800F on both the dome and the floor using an infrared thermometer, you are measuring the inner face. The part facing the fire. At that point, the outer face will be much cooler, depending on how quickly you fired up your oven. From that point on, you can continue firing your oven, and the inner face will stay roughly 800F, and the additional heat will continue to drive up the temperature of the outer face of your dome and floor. That's the stored heat you use when you bake without the fire.

Alternatively, when the inner face of your oven is hot and the outer face is still cold -- and you take out the fire -- the two faces of your oven will meet in the middle to the point of equilibrium, and the entire mass will become only moderately warm. The inner face will cool down and the outer face will wick heat outward.

That's what I meant by "filling" your oven with heat. I tried to capture that with our FB heat graphic.
James
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Old 04-14-2009, 09:16 PM
MK1 MK1 is offline
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Default Re: Hearth Floor

Okay now I get it. I took a closer look at the graphic above and included in the plans. It clearly states that it's showing how the heat moves to the outer edge of the mass. I had read that but didn't have enough background to understand. It takes me a little while. Again I appreciate all the prototyping you've done, and I can't wait to fire it up.. that is, after I finish building it.

Mark
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