Forno Bravo Forum: The Wood-Fired Oven Community

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-   Heat Management (http://www.fornobravo.com/forum/f17/)
-   -   Poll: How hot is the outside of your igloo? (http://www.fornobravo.com/forum/f17/poll-how-hot-outside-your-igloo-10700.html)

kebwi 02-02-2010 04:29 PM

Poll: How hot is the outside of your igloo?
 
For those who have built igloos (I assume enclosures are completely different in this regard but if not, contribute...but explain your enclosure briefly) how hot does the outside of your oven get? Can you estimate it numerically (or have you pointed your thermometer at it)? If not, just characterize it using "warm/hot to the touch" descriptions.

Additionally, to make this information useful, please include a description of your insulation. Blanket? How thick? Loose vermiculite/perlite? How thick? Vermicrete/perlcrete? How thick?

I know I have seen individual reports of this kind of thing throughout FB mixed into threads on other topics and I don't mean to be redundant...but this thread could represent a repository on this specific issue, easily discovered by thread topic in the future...if it accumulates enough data points.

Cheers!

scottz 02-02-2010 04:47 PM

Re: Poll: How hot is the outside of your igloo?
 
Hi,
I have an igloo style WFO. Mine is built of Pre-cast Refactory Cement. I find that my oven is fairly cool for up to 2 hours after getting to 'pizza hot'. At this stage I get a bit of heat coming through the top central part of the oven while the sides and around the bottom remain coolish. In terms of how hot...I would say I can easily put my hand on the top and not burn it, but there is a bit of heat there...dont think it is anywhere around the 100C mark. The insulation that I used was a fiber ceramic Fire blanket that i guess was a good 2 to 3 inches thick. It was then covered to 2 coats of render. I was a little concerned with the heat loss to start with, but since then I have done a fair bit of slow cooking and the oven retains heat enough to do roasts and other things for 8 hours and more, so I guess its ok for the type and length of cooking we do. I know I can have a good cook in the evening and first thing in the morning I can put my hand in the oven and it is still warmish. I hope this helps.

Scott

texassourdough 02-02-2010 05:29 PM

Re: Poll: How hot is the outside of your igloo?
 
My oven is also pre-cast refractory cement finished to FB standards and my oven is never more than warm to the touch - even after three or four hours EXCEPT near the chimney connection where it gets pretty warm over time. And yes, my chimney can get HOT!
Jay

kebwi 02-02-2010 07:15 PM

Re: Poll: How hot is the outside of your igloo?
 
@Jay: Would you mind giving more detail about your instulation? There are multiple prescriptions in the Pompeii directions. You can use a blanket or not, instructions for both are given? Did you use a blanket? How thick? What sort of vermiculite layer did you add?

texassourdough 02-03-2010 06:13 AM

Re: Poll: How hot is the outside of your igloo?
 
Hi Kebwi!

As indicated, my oven starts with a precast dome from FB. I added about an inch of additional refractory cement to give it a bit more mass. Then the refractory insulation blanket which I recall being about an inch thick, maybe an inch and a half. Then foil. Then chicken wire and about two inches of cement and vermiculite. Then stucco. At least that is how I remember it from five years ago.

heliman 02-03-2010 06:27 AM

Re: Poll: How hot is the outside of your igloo?
 
Mine is barely warm (the cats sit on it as proof of its mild termperature).

I would guess that it its tempertature is no different to a brick that has been left in the sun for a while.

Rossco

kebwi 02-03-2010 07:51 AM

Re: Poll: How hot is the outside of your igloo?
 
@heliman: That's great. Let us know how you insulated it.

martywatts 02-03-2010 09:59 AM

Re: Poll: How hot is the outside of your igloo?
 
I have not put a finished veneer on yet, but after the several full firings we have done, the outside of the dome is barely above room temperature. That varies only slightly as you get closer to the entry of the dome where the insulation is not as thick as the rest of the dome. I insulated with 1 to 2 inches of mineral wool then covered everything with 5 inches, more in places of perlite concrete mixed 12 to 1. The dome is as per forno bravo plans using fire brick.

Wiley 02-03-2010 11:24 AM

Re: Poll: How hot is the outside of your igloo?
 
Even after firing for some an extended time there is very little to no detectable difference between the exterior temp of my dome and the exterior temperature of the support base. This is not true near the very top where the chimney exits.

The exterior dome of my WFO is a shell and not supported by the interior mass of the oven but rather is a separate free standing structure. Over the thermal mass of the WFO I have 3 inches of kaowool insulation on the lower side areas and as one moves up the dome toward the top that thickness increases to 4 inches with five or so at the very top. Between the outer surface of that kaowool insulation and the inner surface of my dome shell there is infill of loose vermiculite. This infill varies from about one inch to perhaps as much as three inches.

Hope this helps,
Wiley

3G_ 02-03-2010 11:58 AM

Re: Poll: How hot is the outside of your igloo?
 
I used 3 layers of insulation (25mm thick) My dome gets alot hotter in the sun during the day than during a nights cooking. I would say no hotter than 40degrees C. I was amazed at how good 3 layers of insulation is.


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