#1  
Old 06-20-2014, 03:30 PM
Peasant
 
Join Date: May 2014
Location: Haida Gwaii
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Default To keep the oven hot

I plan to start building soon. Before I do I want to eliminate a few of the "I wish I'd thought of that sooner"' scenarios. It sounds like some people wish they'd used more insulation under the oven. Will a single layer of 2" FB board under my oven will be enough to get results approaching:

"Doored after pizza, 850-900
24 hours 550
48 hours 350
72 hours 200
96 hours 150
120-168 hours ambient"

to be able to, say, bake pizza for dinner, and then use the oven to bake bread and make dinner the next day. For the dome I plan to use a two layers of FB blanket insulation, covered with vermicrete for an igloo finish, and will make an insulated well fitting door. At this time I don't plan to include a thermal break between the dome and entryway (or entryway and decorative arch?), but would do so if it would make a significant difference. I think I need to decide this before I begin construction to alter the layout accordingly. I don't want to make it too complicated / expensive, but also don't want to have regrets about taking shortcuts.
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Old 06-20-2014, 05:07 PM
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Location: Carson City, NV
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Default Re: To keep the oven hot

I'm not sure of the diminishing return on insulation thickness. I used 4 inches and this is what I had (for the record). Also, if your hearth is 850 - 900 after pizza, pretty sure they will be burnt.

Saturday at 6:30 PM after the fire; hearth=900 deg.
Saturday at 8:00 PM after pizzas; hearth=555 deg.
Sunday at 9:00 AM hearth=447 deg. - cooked a coffee cake
Sunday at 4:30 PM hearth=374 deg. - cooked coconut shrimp
Monday at 6:30 AM hearth=288 deg.
Monday at 4:45 PM hearth=244 deg.
Tuesday at 4:45 PM hearth=170 deg.
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Old 06-20-2014, 05:21 PM
Peasant
 
Join Date: May 2014
Location: Haida Gwaii
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Default Re: To keep the oven hot

I'd be quite happy with temps like that.
Looks like I might want to consider doubling the FB board under the oven, but it cost $200 just to ship it here (and I've have to postpone starting).
I wonder if a thermal break, a well insualted door, and an extra well insulated dome would do the trick...
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Old 06-20-2014, 05:58 PM
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Default Re: To keep the oven hot

Try searching for calcium silicate (CalSil) on your island and in British Columbia. I used 2" of CalSil on top of 4" of vcrete. I am very pleased with the results .
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Old 06-23-2014, 09:19 AM
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Default Re: To keep the oven hot

I used 4" of insulation all around and filled the rest with loose vermiculite.
I also used 2" FB rigid insulation underneath, as well as 2" of vermiculite/portland cement under that. I also built a 2" thick insulated door.

If I get the oven good and hot the night before when making pizza, I've had temps as high as 550 the next morning to make bread, and still in the 400's that night.
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Old 06-23-2014, 09:49 AM
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Default Re: To keep the oven hot

i have 3 inches of FB, 3-4 inches of blanket, thermal break, and a 2 inch door.
I get performance similar to Les' numbers. I think the thermal break may give me 5-10% better performance in terms of temp retention (vs. not having it, not vs. you Les ), but it doesn't stretch the cooking time out by a day or anything like that.

FWIW, my experience is that you might get 550 degrees 8 hours after pizza, but not 24 hours after, and you will get that only if you put the door on when the fire is raging. More likely you will put it on after you're done cooking pizzas and the oven will be 700-750 degrees at that point. To have a 950 degree oven, you've got a live fire in there - and once the door goes on it will smoke like crazy. Not really pleasant for guests if the wind is blowing the wrong direction. I doored my oven Saturday night after a pizza party. It was probably 700 on the floor when I put the door on. Late sunday afternoon door thermo showed 425. 36 hours later it's showing 300.

I would add more insulation under to your plan, for sure. Check out McGill's Warehouse for insulation. They have the best prices.
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Last edited by deejayoh; 06-23-2014 at 09:53 AM.
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Old 06-23-2014, 07:21 PM
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Default Re: To keep the oven hot

My numbers are similar to Les', although I live in a much warmer climate in Southern California. My oven floor (1.25" of soapstone atop 2.5" firebrick) is insulated below with 3.5" of vermicrete topped with 2" of calcium silicate board. On top I have between 6-12" of CF/rockwool insulation.

With your climate I would suggest including a thermal break between oven and entryway. I would also consider enclosing your oven in a structure rather than an exposed igloo.

I hope you are not adversely affected by the Little Sitkin earthquake.

John
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Old 06-24-2014, 02:34 PM
Peasant
 
Join Date: May 2014
Location: Haida Gwaii
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Default Re: To keep the oven hot

I checked out McGill's Warehouse, and the prices were indeed good , but the shipping was over $300, and I have not yet locating a more local source for calciam silicate board. But, I fiound out I can get Vermiculite at the animal feed store here, "on island", and so decided to pour four inches of vermiclite / concreate, and put the 2" of FB board I have on top of that. Might be nice to get a feel for "vermicrete". It sounds like the extra effort of adding this will be worth it. Thanks for the feedback.

I plan to first build the arch/dome, and put of deciding if and how to do the thermal break transition to the entryway. But, I do need to know if I should put vermicrite and FB board under the entryway area as well as under the oven.

The entryway arch / vent can be built with something other than fire brick, yes?
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Old 06-24-2014, 03:04 PM
Peasant
 
Join Date: May 2014
Location: Haida Gwaii
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Default Re: To keep the oven hot

Hey John - No impact here from the Little Sitkin earthquake. I hadn't even heard about it before you mentioned it. Too oven focused perhaps. I tend to pay particular attention to quakes since our whole town was evacuated in 2012 after a 7.8 earthquake, and then again a couple months later.

I was hoping that I could get away with an igloo enclosure; I am building the oven under a cover - but it is still exposed to lots of blowing rain.
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Old 06-24-2014, 05:13 PM
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Default Re: To keep the oven hot

I guess your recent quake was downgraded all the way down from 8.0 to 7.9... Good to hear you weren't evacuated again. We went through a solid week of earthquakes a few months back and sustained minor damage, but the only thing I was worried about was my oven!

If you care to post your oven plans before you really get started (including the base and support stand), please feel free. I wish I had done so in order to gather input on design and construction elements that I would face later on. I admit I went into the construction phase of my oven 'blind', but miraculously came out with a tiny percentage of trade-offs or shortcomings in the final construction.
John
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