1" of Thermal Mass VS. 1" of Insulation

[Ken524]

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!

[RTflorida]

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

[Frances]

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.

[rlf5]

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.

[asudavew]

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!

[Ken524]

Re: 1" of Thermal Mass VS. 1" of Insulation

Thanks Ron,

I forgot to add that piece of the puzzle:

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?

[rlf5]

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.

[james]

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.

[james]

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

[Ken524]

Re: 1" of Thermal Mass VS. 1" of Insulation

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

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

Hi Ken,

I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.

It turns out that 1" is the most widely produced thickness, so it is best to just run multiple layers. Overlap the seams, and it will work well.

Two boxes should give you three layers (just about). Go thicker on top, as there is more heat up there.

Have fun!
James

[asudavew]

Re: 1" of Thermal Mass VS. 1" of Insulation

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.

That's great to hear James!

I was getting all worked up for a coat of mortar.... and lots of mixing!

WOOHOO!

Arch and entry way for me!

Thanks for the input everyone.

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

You can still do a thin coat to seal up the oven, and give it a little structural integrity. You can just put it on with a trowel -- no heavy lifting.
James

[Ken524]

Re: 1" of Thermal Mass VS. 1" of Insulation

Hi Ken,
I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.

Are you patching the external cracks with RefMix or some sort of high temp goo?

[james]

Re: 1" of Thermal Mass VS. 1" of Insulation

RefMix. It sets fast, which really helps. Make sure the oven is fully cooled down, and wet the area you are patching before you slop it on.
James