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james 05-30-2006 04:01 PM

Measuring your Hearth
1 Attachment(s)
We get a lot of questions on hearth size for the various oven sizes, and as there is not an "exact" hearth size for each oven, I am posting the method for how you can calculate the hearth size that works for your site.

I am also attaching a drawing that you can use as a worksheet to calculate your hearth size.


For oven width, take the exterior width of your oven (oven floor, plus oven wall width), then add 10" for your insulation (1" insulfrax and 4" vermiculite), then add the thickness of your enclosure walls (1/2" for an Igloo, 2" for a metal stud wall, 4" for a concrete block split, etc.)

For example, a Casa90 (35.4" cooking floor) is 40.1" wide externally. That means the stand for an Igloo enclosure should be 51" wide. 40+10 (insulation)+1 (enclosure walls).

If you are building a 42" Pompeii oven, you have 42 (floor)+9 (walls)+10 (insulation)+1 (enclosure wall) = 62".


For the oven depth, you take the depth of the oven and vent, then add 5" for rear insulation, then wall thickness, and then space for your oven landing.

The Casa90 is 43.5" deep, including the vent. If you want a 12" landing, the hearth should be 43.6 (oven and vent)+5 (rear insulation)+.5 (one wall) +12 (landing) = 61".

The 42" Pompeii oven works as follows. 42 (floor)+9 (walls)+6 (vent floor)+5 (rear insulation)+.5 (one wall)+12 (landing)=74.5".

You can find the dimensions of the Forno Bravo Casa, Premio and Artigiano ovens in the installation guides here:


Balty Knowles 04-26-2007 05:44 PM

Wall Insulation
1 Attachment(s)
My oven design is for a 39" dome leaving 4" for insulation all around to a ciircular brick encasement, 2 bricks thick. I would like to increase the floor size to 42" leaving only 2-1/2" for insulation. I was thinking of using some of the soft white insulating firebricks around the bottom of the dome as insulation between the oven wall & outer brick wall. As the dome curves away from the wall allowing more space I can replace the insulating brick with loose vermiculite.

The white bricks are expensive but I think a bigger oven would be better.

Any thoughts on this.


jahysea 04-26-2007 08:58 PM

Re: Measuring your Hearth

I have a 42" oven and I've never wished it was smaller. Lots of times I've wished it was bigger.

I know insulation is very important, but if it where me I'd sacrifice some insulation around the bottom of the oven to gain the space inside.

If you take the wider dome approach, might be best to get advice from one of the engineers on the very best insulation material for the space you have. I suspect it's a ceramic blanket, but not sure. The blanket could be coated with portland/stucco just like anything else.

This type of use is pretty common for my oven:

DanaMac 03-26-2008 02:10 PM

Re: Measuring your Hearth

New to all this but building the oven this week. Can I double the insulationg blanket and cut back on the thickness of the vermiculite shell?

james 03-26-2008 02:28 PM

Re: Measuring your Hearth
Welcome aboard,

Definitely. That's what I did. Rather then doing 1" of FB Blanket and 4" of Vermiculite, I used 3" of FB Blanket. It's thinner, better insulated and easier to install.


RCLake 03-26-2008 03:10 PM

Re: Measuring your Hearth

Originally Posted by DanaMac (Post 27623)

New to all this but building the oven this week. Can I double the insulationg blanket and cut back on the thickness of the vermiculite shell?

Stongly suggest you do just that. Since I could find both products in Dallas, I found out cost wise it was a push and I think the blanket is better. I've built a 42" Tuscan and 50 sf of blanket will provide half again the thickness. It takes about 2/3rds of a box to cover the WFO, I bought a box of 2" and 1" thinking I would get 3" coverage. I'll almost have 4-5" over it when I'm done.

Balty Knowles 03-31-2008 03:06 PM

Re: Measuring your Hearth
3 Attachment(s)
I was worried about heat transfer to my outer brickwork as I only had 3" of space around the bottom of the dome. I used 1 blanket of insulfrax around the sides & then tamped down any off cuts to fill the gap. I added a second blanket where I could & then filled the cavity with Vermiculite.

After several hours of the oven at temperature there is absolutely no heat transfer to the outside of the brickwork.

I added another blanket on top because I poured a concrete slab as my roof & was worried about heat transfer from the top. Again there is none after several hours of using the oven.

Xabia Jim 04-17-2008 11:09 PM

Re: Measuring your Hearth

Originally Posted by jahysea (Post 9984)

my oven is a meter or about 39 or 40 inches and have stacked oven dishes on top of each other before....terraced cooking I called it.

Is there a post on relative surface area any where?

beth halstrom 07-24-2008 03:09 PM

Re: Measuring your Hearth
I'm installing a Premio 100 (39" cooking floor) and am trying to get an exact stand measurement. If I'm using 2 FB blankets for insulation (omitting the vermiculite) would I need to add 10" for insulation using the chart above? Walled enclosure, not igloo style. The smaller the footprint the better.

Balty Knowles 07-24-2008 04:28 PM

Re: Measuring your Hearth
I can only speak from my own one time experience. I had 2 layers of Insulfrax on the sides but compressed into 3" of space & an extra layer on top as I had it left over. Absolutely no heat transfer through the walls or roof.



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