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Old 08-19-2011, 06:56 PM
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Thumbs up Re: Thermal break between dome and chimney box

I didn't find much on this subject either. But did manage to put heat brakes in three different places on our oven entry. You can see the brakes and read my comments citing actual temperatures here.

If I could go back, I'd make the air space between the dome and the inner arch a bit wider.
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Last edited by Lburou; 08-19-2011 at 07:12 PM.
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Old 08-19-2011, 07:26 PM
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Default Re: Thermal break between dome and chimney box

Quote:
Originally Posted by Lburou View Post
I didn't find much on this subject either. But did manage to put heat brakes in three different places on our oven entry. You can see the brakes and read my comments citing actual temperatures here.

If I could go back, I'd make the air space between the dome and the inner arch a bit wider.
You said you would have a 1/2 inch air gap between the inner arch and the flue but when I look at your photos it looks like it might be about 1/2 inches already, what type of gap do you have now?


Chip
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Old 08-19-2011, 07:37 PM
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Default Re: Thermal break between dome and chimney box

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The 1/4 inch gap seems quite large at the floor but I think the sides could tolerate this type of air gap
True to form, I didn't fully explain the configuration of my gap. I plan to maintain a continuous brick surface between the arch and entryway via the entryway brick that butts up against the inner arch (see illustration) The contact area in this graphic has been set at 1" and the gap here is 1/2". This is my idea of a thermal break. I could make the contact area less than an inch but am concerned that over time thermal cycling may make the portion of contacting brick brittle and subsequently break. My other thought was to leave a true (1/2" gap) and fill it with say, a 1/2-1" strip of 1/8" -thick stainless steel on the inside and insulation (or not) behind the stainless.

My plan right now is to incorporate a stainless steel entryway floor so there will be no gap between the entryway and oven floor.

Any thoughts?
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Old 08-19-2011, 08:08 PM
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Default Re: Thermal break between dome and chimney box

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. My other thought was to leave a true (1/2" gap) and fill it with say, a 1/2-1" strip of 1/8" -thick stainless steel on the inside and insulation (or not) behind the stainless.

My plan right now is to incorporate a stainless steel entryway floor so there will be no gap between the entryway and oven floor.

Any thoughts?
The idea of stainless at the entry is a great idea from more than one perspective. The entry floor can be easily cleaned and the underlying area could be entirely insulation no need for conducting brick mass there.

The stainless could be bent down at the edges and provide a nice clean edge that would not catch tools and it would provide a turned down wrap over the insulation below.

I have been toying with the idea of a metal bumper strip at the edge of the inner arch to prevent what others have experienced and that is excessive chipping of the edges of the inner arch.

If a piece of stainless angle was placed at the corner of the inner arch and wrapped around the inner arch it would create a nice strong corner. It could be built to fit loose enough to not cause any thermal expansion issues.

The problem would be fabrication of this very unique shape. I am not sure if you could heat angle with a torch and get it to bend into such a radical curve.

See drawing for below

The other possibility is not to use angle but a larger sheet or a number of smaller sheets that just sit between the inner arch and the entry arch. The material does not really need to wrap around the corner into the entry of the oven it just needs to protect the corner. Cutting the stainless to match the arch would be quite easy. And multiple pieces could be cut to lock together to prevent shifting. Additionally attaching a piece of insulation gasket rope to the stainless should be a piece-o-cake and further secure the stainless should they be multiple pieces.


Chip
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Last edited by mrchipster; 08-19-2011 at 08:28 PM.
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Old 08-19-2011, 09:30 PM
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Thumbs up Re: Thermal break between dome and chimney box

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Originally Posted by mrchipster View Post
You said you would have a 1/2 inch air gap between the inner arch and the flue but when I look at your photos it looks like it might be about 1/2 inches already, what type of gap do you have now?


Chip
Its about 3/16ths of an inch. What I want to communicate is that I wanted more of a temperature difference between the dome and the inner arch. I don't think my design hurt the performance of the oven....But, a slightly larger gap could make a larger temperature difference.

The sixteenth inch gap between the granite and firebrick on the entry floor gives about half as much temperature difference as the difference between the inner arch and the dome, ergo, the larger the gap, the slower the heat loss. The question is, how big a gap is too much? And, where does the thermal brake do the most good?
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Old 08-19-2011, 09:44 PM
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Default Re: Thermal break between dome and chimney box

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The question is, how big a gap is too much? And, where does the thermal brake do the most good?
Not having a great deal of experience in thermal transfer I do not know but I believe you are on the right track and since your oven is built and you have experimented I will strongly consider your experience. Many thanks for your insights.

Chip
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Old 08-19-2011, 10:29 PM
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Default Re: Thermal break between dome and chimney box

This is where I placed mine. I filled the bottom with 7:1 vermicrete which has some elasticity, did the same at the top, but didn"t worry about filling the sides. Because of the design of my floor, I couldn't put the gap at the inner end of the entry.
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Old 08-20-2011, 04:38 AM
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Default Re: Thermal break between dome and chimney box

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Any thoughts?
One other important thought. an L shaped brick like you propose will induce significant stress at the corner I highly recommend a smoother transition for your corner. Cutting a near 45 degree angle and then smoothing the transition with a grinder might be the way to go.

Chip
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Last edited by mrchipster; 08-20-2011 at 07:25 AM.
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  #19  
Old 08-20-2011, 10:09 AM
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Default Re: Thermal break between dome and chimney box

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an L shaped brick like you propose will induce significant stress at the corner
You may be right. My initial thoughts are that a hemispherical entryway will stand on its own weight, simply butted up against the oven inner arch. A workaround for the L-shaped tab might be the near-45degree cut brick with a shallow angle cut filled with high-temp silicone. Another option might be a stainless steel insert, an option for me because of a brother who is highly skilled at fabricating all kinds of steel.

I guess great minds think alike, yes? I have two designs in mind for the stainless steel entryway floor, again to be fabricated by my bro. I like the idea of sealing the door with ceramic rope. Here is my idea of incorporating it into the (FB designed) door instead of remaining exposed to elements.
John
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Thermal break between dome and chimney box-thermal-break-2.jpg   Thermal break between dome and chimney box-stainless-steel-entry-floor-1.jpg   Thermal break between dome and chimney box-stainless-steel-entry-floor-2.jpg  
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  #20  
Old 08-20-2011, 12:50 PM
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Default Re: Thermal break between dome and chimney box

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Originally Posted by GianniFocaccia View Post
You may be right. My initial thoughts are that a hemispherical entryway will stand on its own weight, simply butted up against the oven inner arch. A workaround for the L-shaped tab might be the near-45degree cut brick with a shallow angle cut filled with high-temp silicone. Another option might be a stainless steel insert, an option for me because of a brother who is highly skilled at fabricating all kinds of steel.

I guess great minds think alike, yes? I have two designs in mind for the stainless steel entryway floor, again to be fabricated by my bro. I like the idea of sealing the door with ceramic rope. Here is my idea of incorporating it into the (FB designed) door instead of remaining exposed to elements.
John
I made a modification to the sketch in a couple of ways.

1) I believe the L shape is very strong just not a sharp corner at the 45.

2) hi temp silicone might be a good idea I do not know what it is heat rated for.

3) Take out the first metal flange from the door removing the U and leave the outer edge an L shape for the rope to sit in.

I like design 1 for the floor as it keeps the entry devoid of things that will catch the oven tools.

Chip
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