Driving heat across the cooking floor

[brickie in oz]

Re: Driving heat across the cooking floor

a question,
please redirect me if I am in the wrong place.
I am at the stage of base nearly complete and about to lay the floor / hearth.
3 inches of Hebel (aerated concrete) 2 inches of cal sil and 3 inches of fire tile.
I would like to make provision for thermocouples, either a tube or the device itself.
Any thoughts re material, placement, number , other relevant detail would be appreciated,
Oven is to be 42 inch diameter hemispherical shape much as per forno bravo plans.

Thanks

Dave Ly

Dave you will get more replies if you start your own thread, unless you have the answer you seek.

I've been curious as to why one would want thermocouples. The hassle of installation, expense of purchase, display, etc... They are very cool but why not just shoot whatever with the laser. At the end of the day, we just want to know the temp, right? The laser is working for me but am I missing something? It seems like a lot of effort for little reward. JMO...

Same Les, nice toy but the laser gives me all the info I require too.

[Les]

Re: Driving heat across the cooking floor

I've been curious as to why one would want thermocouples. The hassle of installation, expense of purchase, display, etc... They are very cool but why not just shoot whatever with the laser. At the end of the day, we just want to know the temp, right? The laser is working for me but am I missing something? It seems like a lot of effort for little reward. JMO...

[david s]

Re: Driving heat across the cooking floor

I have a thermocouple ( an old fashioned anologue type) in the side of my oven. I placed it about half way up the dome and used some stainless steel tube as a protective sheath for the probe. Stainless steel is not as good a conductor as copper. The sheath should not be a tight fit in the inner dome otherwise it will push out as the oven expands.

[david lyons]

Re: Driving heat across the cooking floor

a question,
please redirect me if I am in the wrong place.
I am at the stage of base nearly complete and about to lay the floor / hearth.
3 inches of Hebel (aerated concrete) 2 inches of cal sil and 3 inches of fire tile.
I would like to make provision for thermocouples, either a tube or the device itself.
Any thoughts re material, placement, number , other relevant detail would be appreciated,
Oven is to be 42 inch diameter hemispherical shape much as per forno bravo plans.

Thanks

Dave Ly

[cuda]

Re: Driving heat across the cooking floor

That idea crossed my mind for a hot second (no pun intended), but I'm not interested in doing the floor twice. Actually, I'm really only curious for academic purposes. I'm sure that the countless ovens that have low-duty brick floors work great- I was merely wondering if anyone had any theoretical or practical experience with higher-duty floors for pizza.

[nissanneill]

Re: Driving heat across the cooking floor

Then the solution is easy to decide.
Get your high temp bricks and try to cut them to fit "inside" of your full height soldier 1st course bricks. Build your oven as you wish and if you are not happy with the hearth performance, you simply remove it and replace it with the low fire bricks. In other words, don't build your oven on top of your hearth bricks.

Neill

[james]

Re: Driving heat across the cooking floor

Three times the cost is reason enough for me.

In reference to medium/high duty brick: Would it keep the floor hotter, thereby making a better floor for pizza cooking, or just hold more heat for a longer period (btu vs. temperature), all other things being equal? Sounds like for our purposes there is no appreciable difference.

I heard good advice from the pro who builds the Artigiano oven. He can use any brick, and chooses a purpose made oven brick with alumina content around 30%. He says, "we cooking food here, not melting metal."

I like that.
James

[DrakeRemoray]

Re: Driving heat across the cooking floor

From The Bread Builder's by Alan Scott and Daniel Wing:

"For ovens, it is fine to use standard low-duty 'fireclay firebrick,'...good to about 2,700 degrees Fahrenheit (1500 degrees Celsius), which is far above the temperatures you will ever achieve in your oven. Higher-percentage alumina bricks are more resistant to heat and abrasion (good for pizza hearths) but they have a disadvantage in bread ovens: the higher alumina brick is more conductive and may transfer an excessive amount of heat to the bottom of the loaf. Also, High-duty firebricks are actually less resistant to the cycles of heating and cooling such as those experienced by oven brickwork and are more likely to crack, spall and fail than standard firebrick. Low duty firebrick contains tiny voids into which the solid material of the brick can expand when it is heated."

That said, I am used medium duty in my oven (it is all I could get). I do experience burnt bottoms of my bread if I don't let the oven cool enough. (For the record, I think it is not that easy to cool the oven. I have to wait hours before I can bake after firing for pizza). I would not advocate having the hearth bricks on their thick sides. I have been regularly baking 25 lbs of bread after a pizza firing (I do have about 1" of extra mass - heatstop - on the dome, but no extra mass on the hearth), and I still cook a roast (or 3 last weekend) the next day, I don't think any extra mass in the hearth is needed. I know you this is just more conflicting advice, but in general, the standard plans seem to work the best: Low duty firebrick, hearth bricks on their flat sides, lots of insulation. If you plan to use your oven only for pizza and never for bread, you could consider the high duty bricks. But you will make fabulous pizza from a low duty brick oven and may have more trouble with bread from a high duty brick oven...

Hope that helps.
Drake

[cuda]

Re: Driving heat across the cooking floor

Hmmm...conflicting opinions....

I guess I'm not that worried about extra cutting time or effort for just the floor since I'm not going to be cutting that much (I think). If the high-duty brick would really make a difference over the many, many years I plan on using the oven, it would be worth it. Trouble is, I have no way of knowing if it would or not.

[nissanneill]

Re: Driving heat across the cooking floor

Hi Cuda,
Take Dmun's advice with regards to cutting the high temp fire bricks. In the 200 odd second hand fire bricks that I got for my oven, there were around 6-8 high temp bricks amoungst them. I was thinking of using them for my first course of soldier bricks until I cut the first one, No exaggeration, the 14" diamond saw (proper brick cutting saw with a brand new diamond blade) was like cutting a slab of steel. It took up to 10 times the effort to cut the 15˚ required to set the second chord on the correct angle thus reducing the mortar joint thickness. Don't even try cutting them with anything less than one of these saws. The brick are also around 1.5 to 2X as heavy as the low or medium bricks.

Neill

[gjbingham]

Re: Driving heat across the cooking floor

Cuda,
I kind of like your idea about the high duty firebrick floor. I strongly support laying the floor bricks on their sides for a little extra mass to maintain a hot floor while cooking.
I haven't looked at the properties of low duty v. high duty bricks. There's probably information on the web describing the heating and cooling curves of the two brick types. You will expend a bit more fuel to get the oven to pizza temps but my guess (and I mean guess) is that with HD bricks, the floor will definitely cool much slower.
A review of many of our ovens performance's show that there are many bricks available across the country, or around the world, that result in drastic differences in heating and cooling times. I suspect that this is due to the use of the different types of bricks, and less so, on the insulation surrounding the oven. Pretty much everyone seems to follow those guidlines, or at least should.
Regarding the ease of cutting issue, if you're only going to use them on the floor, there will not be that many cuts anyway. I used a HF saw to cut standard masonry bricks for my decorative arch. Brutal! Much much harder than firebrick. Slow, loud, slow slow slow going..... but an hour's work (max) should get you through all the cuts you need for a floor (again - a guess).
Hope that helps. Just my stinky opinion.

[Ageo308]

Re: Driving heat across the cooking floor

From what I think I read on the forum (really decisive information here), high duty fire bricks can make the floor too hot for pizza.

James, I'll let you know how my new high tech tool works out...

Its much easier to cool down an oven then to heat it up, In my opinion if your going to spend a decent amount of time and money in building a custom oven then why not go for the best you can afford?

[Frances]

Re: Driving heat across the cooking floor

From what I think I read on the forum (really decisive information here), high duty fire bricks can make the floor too hot for pizza.

James, I'll let you know how my new high tech tool works out...

[cuda]

Re: Driving heat across the cooking floor

Three times the cost is reason enough for me.

In reference to medium/high duty brick: Would it keep the floor hotter, thereby making a better floor for pizza cooking, or just hold more heat for a longer period (btu vs. temperature), all other things being equal? Sounds like for our purposes there is no appreciable difference.

[dmun]

Re: Driving heat across the cooking floor

High duty fire brick is denser and harder. It cuts slower, but it cuts. If you are setting your dome on the floor, which I like, you should cut your bricks that stick out a lot, so they are within the insulation envelope.

A hint for cutting hard materials, which I learned too late, augment that wimpy stream from the pump with a spray from the hose. It prevents the blade from grabbing, shimmying and bucking.

On a good saw, low duty firebrick cuts like balsawood. It's the easiest masonry item to cut.

Again, if you want to use high duty firebrick, go right ahead. Report back. We stand to learn something.

It's been a while since I've been shopping but ordinary fireplace bricks can be had from a masonry supply for about a buck a piece. High duty bricks are a refractory special item, and could cost you 3 bucks plus, and might not be available locally.