Thermal mass needed in Bend, Oregon Pompeii Oven Construction Discuss Thermal mass needed in Bend, Oregon in the Pizza Oven Design and Installation forums; Hi all, Reading the plans, I decided to put in an extra layer of fire brick above the insulation layer ...

[jefekefe]

Hi all,
Reading the plans, I decided to put in an extra layer of fire brick above the insulation layer for extra thermal mass since I live in Bend, Oregon where it can get cold, and also because I want to bake bread. Is this a bad choice? I've read some posts that too much is a bad thing. Please advise. Should I pull up the layer, or use splits for the oven floor, or simply leave it and go with my first instinct?

[Breven]

Good question. I think that the heat radiating from each brick will spread to the next brick. I think too much thermal mass will cause your oven to take langer to heat up, becuase essentially all of the bricks will want to heat up together. The idea is to block the heat from radiating beyond the bricks of your oven with insulation- not more fire bricks. But I'm not an expert, that's just my gut instict too.

[RTflorida]

Unless you are baking commercially (several or many back to back loads of bread), anything more than the standard 2 1/2" mass is overkill. More mass equals longer heat up times and more wood consumption. If you are the average WFO builder who wants to make pizza and then throw in a load of bread or two as it cools down you will be totally fine (provided you have followed the insulation guidelines). That said, insulation is by far the most critical veriable in oven performance. More is better, a lot more is ideal.

RT

[MK1]

I had thoughts like yours when planning my build and questioned a lot of the more experienced builders and bakers here. Everyone was very helpful and my confusion eventually cleared. I read a lot of old posts and found that just about every variation has been tried. I also slowly began to understand the dynamics of the oven.
I kept my floor 2.5" thick and added 1.5 inches of homebrew refractory mortar to the dome. I'm very happy with the results. The dome is the heat source. A thicker dome = more heat up time and also more heat reserves for longer operation and more stable temps. You also have to wait longer for temps to drop with a thicker dome. Floor thickness = floor temp charge time or reactiveness. A thicker floor will take longer to recharge from the dome (heat source in the oven). I suppose a thicker floor would also tend to cook the bottom of the loaf too fast.
I was elated after my first bread baking sessions to see almost the same degree of doneness both bottom and top of the loaves. This is a well proven design that will work in any temperate climate. If you change anything, add insulation.

Mark

[Jed]

Hey jefekefe,

Welcome to the forum, and congrat's on deciding to build an oven. The oven in our back yard has been a great addition to our house!

We live in Bend, near Juniper Park. I built the oven just over a year ago. I followed the plans, using the Perelcrete insulation below one layer of fire brick for the oven floor. For our application (home use, standard pizza party followed by two days of cooking) this amount of thermal mass is just fine. If I would change anything on my build, I would have invested in the higher quality insulation under the oven. I think the Perelcrete works just fine, but I think the insulating boards work better.

Once the oven is installed, and cured, it really doesn't seam to make much difference what the weather is outside. The fire will heat the masonry and if it starts at 20 degree's or 70 degree's, the 50 degree difference isn't much relative to the 1000 degree fire...

If you want to stop in and see our oven some time, send me a note at the private messages link on this forum and I can get my contact info to you.

Good luck with your build!

JED

[mluttropp]

Your post states you want to put extra mass above your insulating layer. I hope I am not following your question correctly, but you want your insulation to be the last layer that way it holds all the heat in.

[james]

Hey jefekefe,

It sounds like you are thinking making your floor mass thicker because you want to bake bread. Let us know if that is right.

There has been a lot of evolution and learning as our community has built and installed thousands of ovens, both Pompeii ovens and Forno Bravo modular ovens. Years back when we first started, there was some concern that a single 2"-2.5" floor would not hold enough heat for serious bread baking. Some of us had build Scott ovens, which have 9" thick floors. The early versions of the Pompeii plans and the Forno Bravo installation guides reflect this background.

What our experience has shown is that a 2"-2.5" floor is perfect for both pizza and break baking. I always point out that the FB Modena commercial ovens have a 2 3/4" cooking floor and are used by many restaurants for baking bread each morning. You can bake full loads of bread -- and even bake multiple batches of bread with a well-fired oven with a standard 2-1/2" floor.

Meanwhile, I have tried to re-write the Pompeii Oven eBook and the FB manuals to say that extra oven mass (top or bottom) is only necessary for commercial bread baking -- not for hobby bread baking.

I hope this is helpful.
James