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Old 10-23-2007, 07:46 AM
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Default 1" of Thermal Mass VS. 1" of Insulation

I'm close to finishing my dome and I'm trying to decide whether to clad it with an inch of HeatStop mortar for thermal mass or use that inch for extra insulation blankets/loose vermiculite.



I really like the idea of cooking the next day without re-firing the oven.

Will the extra inch of mass make a big difference in the performance of the oven or would it be splitting hairs? Would I be better off using that inch for insulation?

Also, will cladding the oven make it more susceptible to cracking?

Thanks!
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Last edited by Ken524; 10-23-2007 at 07:51 AM. Reason: Added photo
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Old 10-23-2007, 08:16 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

Hey Ken,

I added about 1/2" - 5/8" of heat stop and then topped it with a 2" blanket and 3" vermiculite concrete. I didn't add the heat stop for added mass, just to give it a smooth/even finish before moving on.
I then finished with 1" of Type N mortar and my mosaic tile.
YES, after every pizza bake (usually late afternoon or evening) I am able to roast something the next day. I usually leave the coals in the oven and close the door overnight...the temp is usually in the 350 degree range the next morning and will hold round or above 300 for most of the day - If i keep the door in place. My door seals well but is not insulated. I think some sort of insulated door would really help, but I am pretty happy with what I have.

RT
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Old 10-23-2007, 08:22 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

I hope you don't mind me butting in here, but I've been wondering the same thing. To clad or not to clad?
Another question I've got: is the cladding structural i.e. does it make the oven stronger? (Obviously less of an issue on your oven Ken than on mine...)

Just from gut feeling, I would have thought an oven would be more likely to crack with cladding.
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Old 10-23-2007, 08:41 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

An inch is really a lot of mass. You could probably get by with 1/4" if you really want to clad it. You'll already probably have longer firing times due to your use of medium duty bricks. If free space is a concern then I'd lean towards the insulation.
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Old 10-23-2007, 09:05 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

Good question Ken.

I was wondering the same thing. So I guess my mess of mortar on the outside will suffice!
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Old 10-23-2007, 11:08 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

Thanks Ron,

I forgot to add that piece of the puzzle:

Quote:
Originally Posted by rlf5 View Post
You'll already probably have longer firing times due to your use of medium duty bricks.
So, the medium duty bricks will retain the heat longer? Is that because they are more dense?
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Old 10-23-2007, 11:15 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

I think they have a higher aluminum content, but I'm not totally sure. The composition is different from light duty though. If you don't have any cracks I woudn't worry about it at all....or I'd just apply a thick coat to the joints to make sure.
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Old 10-23-2007, 11:16 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

I definitely think that you should put that space into more Insulfrax. At a half brick your dome is already thicker than a commercial Italian pizzeria oven -- many of which bake bread every morning from retained heat.

Sometime I think that the Bread Builders book got everybody off on the wrong foot regarding oven thickness and mass. I remember building my barrel vault oven and thinking "cool, the walls are 9" thick; it must be better than those lighter ovens." Years of experience later, I figured out the different demands of a commercial bakery and a home chef.

Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.
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Old 10-23-2007, 11:21 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

On the firebrick topic, the medium duty bricks have a slightly higher alumina content, so they are more heat resistent and more efficient at absorbing heat, but that does not translate into better heat retention. Conductivity works in both directions -- faster heat up and faster cool down. That is good for live fire cooking such as pizza, where you want your oven to recharge as efficienty as possible from the fire to maintain high heat. It has very little impact on retained heat cooking, such as bread and roasting.

I want to emphasize again how good these ovens are at retained heat cooking. You will be amazed and you will be able to bake more bread than your entire neighborhood will be able to eat! :-) You don't need more mass.

James
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Last edited by james; 10-23-2007 at 11:23 AM.
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Old 10-23-2007, 11:33 AM
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Default Re: 1" of Thermal Mass VS. 1" of Insulation

Quote:
Originally Posted by james View Post
Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.
Great news. Thanks for the advice James. The dome stays clean.

What I plan on doing is throwing on the blankets, curing, then building the enclosure. That way, in the event of Cracking During Curing (CDC), I'll be able to deal with it.

James, I think I can squeeze in 3" of blanket insulation. Does Insulfrax come 2" thick or only 1"? How far will a 50sqft roll go for a 42" dome?

Thanks
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