#1  
Old 04-22-2009, 09:36 AM
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Location: Monument, Colorado
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Default Heat break?

I am planning out a build of a Pompeii oven. In reviewing the FB PDF file on the Pompeii oven (a wonderful resource, BTW) as well as the many great posts on the forum, a question comes to mind. There is a lot of attention paid to adequately insulating the oven for efficient performance (reaching pizza temperatures rapidly with minimal fuel as well as good retained heat for other baking).

In considering the design, it seems that there is weak link (in terms of thermal performance) where the mass of the entry meets the mass of the oven dome and floor. In the situation where the fire is out and an insulated door is in place to retain heat for cooking, wouldn’t this continuity between the mass of the oven itself and the entry arch and floor be the source of significant heat drain?

It seems that some kind of heat break between the oven and the entry would significantly improve performance without adding any significant expense. Is there a reason, structurally or otherwise, why a heat break is not used here?

Any thoughts would be appreciated.

Mark
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  #2  
Old 04-22-2009, 12:24 PM
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Default Re: Heat break?

It has been discussed before (I forget where right now) and the verdict was that it wasn't really worth the bother - the heat loss not being big enough to weigh up the fiddling around constructing a heat break. I believe Ken had some neat ideas on how it could be done.

Stucturally of course its better to have the entry firmly meshed in with the oven dome and any kind of heat break will weaken that link. But I'm also quite sure that it is doable, if you really fancy the extra work...
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  #3  
Old 04-22-2009, 01:07 PM
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Default Re: Heat break?

Yeah, I tinkered with some ideas. I think I posted a few drawings on the official "Heat Break" thread; but I ended up sticking to the plan and not worrying about it.

I agree with Francis. You will compromise structure and it's probably splitting hairs anyway.

If you follow the plans, you will be amazed at how well the oven performs.
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Old 04-22-2009, 02:28 PM
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Default Re: Heat break?

my entry way is made of bricks on their thin side so their conduction path is a bit less than bricks on thick side, but I'm very happy with the performance.

One thing I wonder about the floor - it accepts heat from the dome and other radiated sources - but as each brick does not fully contact the other - ash being the insulator does it make a significant difference on heat transfer?

My design required my entry to contact the dome to support the opening. I'm looking forward to seeing your descision and to see how performance is if you go to the isolated dome.

Christo
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Old 04-22-2009, 08:07 PM
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Default Re: Heat break?

I did build a "heat brake" if you will into my entryway floor. My initial goal was not so much efficiency but to keep the temp down on the floor of the arch and landing. You would never know by looking that it is there. At the seem of the entryway floor I cut the side of the joining bricks (first ones outside) at 45deg angle. From on top you see no difference, but a side view would see that the bricks are only touching at the very top edge. I filled the empty space with vermiculite concrete.

Probably not a significant amount of "braking", but it was the only thing I could think of that would be invisible. Can't say what difference it makes, as I have never felt anyone else's oven, but I can measure a difference between the two points of the floor. Has been too long since I was all geeky with measurements, I seem to remember being in the 100+ degree range.

If anyone is interested I can measure next time I fire it up.
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Old 04-23-2009, 07:24 AM
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Default Re: Heat break?

Thanks for the input everyone.

Wade, I find what you did to separate oven floor from the entry floor intriguing. If it occurs to you the next time you fire it up, I’d be interested in hearing what the temperature differential is.

Christo, I had the same question about how much heat transfer there is to the bricks of the entry floor considering the less than complete contact from brick to brick and the ash filling the small voids. Perhaps someone else could measure the differential to compare Wade’s results.

Frances and Ken, tell me what you think the compromise in structural integrity would be to isolate the entry from the oven. I am considering a single brick wide arch attached to the oven dome and a detached arched entry/chimney. The separation between the arch on the dome and the arch on the entry would obviously be sealed. Does that make sense?

Mark
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Old 04-23-2009, 08:22 AM
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Default Re: Heat break?

Please measure next time you fire up.

I'll measure mine without a break at 4 inches inside the oven and 4 inches inside the entry and report also.

Christo
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Old 04-23-2009, 08:32 AM
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Location: Littleton, CO
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Default Re: Heat break?

Even if you gain a few degrees by building a heat break, the biggest problem I have when baking is getting the oven to cool down fast enough. Retaining heat is not an issue in a properly insulated oven, even with the potential leakage you mention.

See this thread for temps over time on the standard build.
http://www.fornobravo.com/forum/f30/...cord-6502.html (Temperatures - for the record)

Also, always welcome another coloardo builder! Where in Colorado are you?

Drake
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Old 04-23-2009, 02:39 PM
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Location: Monument, Colorado
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Default Re: Heat break?

Hi Drake,

I'm just north of Monument, CO.

It sounds like it's been a few years since your build--did you source your firebricks locally? Do you recall where you got them?

Mark
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  #10  
Old 04-23-2009, 04:03 PM
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Default Re: Heat break?

You bet!!

I got my firebrick and the decorative stone surrounding my oven from Robinson Brick (303) 783-3000.

I got the casting stuff for my cast vent and insulating blanket and board (which I used to make my door but would work under the oven) from a refractory supplier called United Western Denver (303) 388-1224

I got the loose perlite from American Clayworks 303-534-4044.

The hardest stuff to find was the dry heatstop mortar. You can try Hillen Corporation - Colorado Demolition and Building Materials up on the north side of town. But I would confirm it is the dry mix, not the airset/premixed...

Good luck! Let me know if you have more questions!
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