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Old 05-11-2006, 09:01 PM
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Default Appropriate Heat

Purchased a thermo laser guide to monitor heat in the oven. Fird the oven for the 4th time. Some of the ceiling bricks turned a white color. The dome heat at about 45 minutes w/ a med to large fire got to about a max of 600 deg on the opposite side of the fire. Other ceiling areas got to about 500-550 deg. The floor got to a max of 375 deg. I know I still have a few more firings before cooking actually can take place with good results. What are some temps to look for? How long will the dome and floor hold the heat? I have heard the flour test on the hearth floor not sure how long before it should get brown though. Any tips would be great.

Steve
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Old 05-12-2006, 10:56 AM
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a big fire is inadequate. you need a "frightening" fire. one where your wife comes out and takes one look and then begins to berate you. a fire where the kids start saying "WOW dad that's cool. add some more wood!" best to overshoot your desired temp and then let the oven come down to cooking temperature. you get more heat stored in the bricks this way (i think).


the hotter the better. my thermo gun goes to 999 degrees and i've had it reading --- (dash dash dash) which indicates over 1000 F. in my experience, i like to roast with the temp of the side wall about three bricks up, starting at about 700 - 800 F and then falling to about 600 over the course of cooking.


with respect to pizza, you (or at least i) can't have the oven too hot. i use a side wall temp of 800 +. however, my first pizza always is problematic (tendancy to burn) and then subsequent ones are easier. i think the first pizza sucks some of the heat out of the hearth and then the radiant wall heat and the hearth heat are in balance. if i don't get the walls hot enough then the tops cook too slow (but i have a high dome compared to most).

in any event, experimentation is half the fun and dough is cheap !!!
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Old 05-12-2006, 01:31 PM
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Default Heat Management

Steve, Robert,

Sigh, guess it's a FB day for me. Robert's very correct in his observations, in my experience at least. One proviso in what follows, I'm a bread guy, primarily.

First off, all the ovens discussed on this forum are classed as "black," meaning the fire is directly in the bake chamber. It's never ready for anything until ALL the bricks turn from black to white, hence "white hot."

Steve, your floor temp is way too low. When mine's ready to go for bread, the floor temp will be in the 700 range, dome bricks very close to this. Rule of thumb: your AIR temp will be about 75 F lower than the hearth brick temp. My oven has four thermocouples, so I know to a degree where the bricks are. Problem for me is finding an air therm that goes higher than 600 F, so I'll be absolutely sure that the air temp is neither too high nor too low compared to the brick temps.

When my oven is really firing nicely, I'll take off the draft door and have a chat with the plasma beast from Star Trek. The air is literally on fire. That's Robert's monster fire at work.

"Overshoot" is exactly right. I bring my hearth brick temp up close to 1000 F, then let the oven relax for about an hour or so, so the temps equilibriate in the bricks and lots of heat gets stored in the cladding (the secret to multiple bakes). If it's still too hot, I remove the door for a while until it's where I want. I normally bake round rustic style breads at an air temp of approx 600-650F; higher for some breads. For pizza, you want it quite a bit hotter than that, with a good fire going in the back and on the sides.

I don't use the flour test anymore, not reliable enough.

The length of time the floor and dome will hold the heat is directly related to the thickness of your slab, insulation layer below, cladding above and insulation above. You'll have to trial and error that one. I bake on Thursdays, and come the next Thursday, my hearth bricks are still at about 200 F from the previous week. But my oven is very high mass. You can try building a sizable fire the night before you plan your main firing. This speeds up the firing time on the day, especially if the weather is cold.

Once I get the pics together, I'll be posting a method to retrofit, or add additional, insulation below the hearth and insulation layer. Quick and cheap to do, with very dramatic results.

Robert pegged it properly. If the kids grin and say that, you're on the right track. My neighbours say something like, "Holy cow, get out the hose, honey, AND call the fire department." Then you're cookin.

Don't forget, you'll get what I call flash heat very quickly on the brick surfaces, but this does not mean the heat has penetrated to the degree that it's useful for baking. Prolonged monster fires are required. How prolonged depends on your particular oven. Just be prepared to experience and eat a few failures. Carbon is good for you, just like Guinness.

Jim
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Old 05-12-2006, 02:39 PM
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The first one always goes to the pizza gods. Just don't put your child's (or neighbor's) perfect pizza in first.
James
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Old 05-12-2006, 06:23 PM
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a pizza oven fired in fear is a pizza oven half fired ...

(with apologies to strictly ballroom)

...
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Old 05-20-2006, 02:23 PM
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Quote:
Originally Posted by Robert Musa
(but i have a high dome compared to most)
Robert, How big is your oven floor and how tall is the dome?

Thanks,
Drake
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Old 05-25-2006, 03:34 AM
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Default Insulation Below

Drake,

Haven't had time to get the pics together for the added insulation I used, but looking at them, they don't really say all that much. The vermiculite layer below my high mass oven is six inches thick. Crawling in underneath one day while the oven was firing to retrieve an errant beer cap, I noticed that the vermic layer wasn't just warm, it was very warm. Not good. Too much heat loss. To correct the problem, I force fit pieces of one inch thick compressed fibreglass insulation board with shiny foil on one side (this is the kind of stuff used underneath vinyl siding; the reflective foil is key; foil facing up toward the hearth). One inch was the thickest I could get. The brand available here is Johns Manville AP Foil Faced Sheathing. Sealed the seams with aluminum tape, the sort used by furnace guys. Over that, I force fit inch and one half thick Dow blue foam insulation, the short that's shiplapped for use on foundation walls, and taped the seams. To make sure the sandwich stayed in place, I cut some battens from scrap plywood and used tapcons that reached into the vermic layer. The results were immediate and impressive. I can get that beer cap without noticing any heat loss, and the slab heats faster and holds heat much better than it ever did.

My hearth is large, so there's a block support column in the middle; covered that in the same way, although there seemed to be surprisingly little heat bleed into it.

This is cheap, easy, and fast to do, doesn't show, and means I use less wood.

Jim
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Old 05-25-2006, 09:46 AM
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Default Moved to "Heat Management"

(M) I moved this posting here as it is a more appropriate venue than where it was

=============================================


"Where there is smoke, there is fire!" may not be true.
Quote:
Originally Posted by arevalo53anos
Hi, Marcel

(L.A.) Nice to talk with you again.
Thanks Gosh, even if my English is not better, my oven do really is.

(M) Your English is about 1,000 times better than my Portuguese!

<snip>


(L.A.) The internal dome size (baking zone) is 41 inches (exactly the size of the plastic blue table top that you could see in the pictures). Do figure that?

(M) I could not find the table top but I take your word for it that you were lucky to find one just the right size.

(L.A.) The damper is used when the fire is in the ‘baking pizzas’ regime, meaning: hottest the chimney, better and greater the flux of gases by it, then more hot air extracted/suctioned from the oven. The damper let you equilibrate this equation to optimize the use of wood.
May be you lost some eyebrows until reach the equilibrium LOL

Luis




===============================================

(M) We also have a saying: "Where there is smoke there is fire." but I'm not sure that is always true. The converse of that saying: "Where there is fire, there is smoke." may also not be true. From your picture of the roaring, eyebrow searing fire you have, I see no smoke. But certainly you must generate some smoke when you first start a new fire? It must be that at that early stage that you keep your damper open? ____

(M) But even a roaring fire must generate a little smoke? ___

(M) If you then close your damper, that little bit of smoke can no longer exit up the chimney. But it can not continue to accumulate in the oven or the CO2 would kill the fire. So it must blow out the front ? ___

(M) You suggest that closing the damper heats the chimney flue and that causes a better (draw) (draft?) into the fire. About how long do you keep your damper closed, and at what point in time do you close it? ___

(M) I am perplexed!

Obrigado,

Marcel
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Old 05-26-2006, 11:51 AM
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Marcel:

Uauh! It comes my Portunglish/Spanglish broking minds, again
Could I explain it?. Will see.
Let´s begin with the damper function.
The chimney that I had choose is a tubular/cylindrical one. This decision had two principal reasons, the first one is that it was easy to obtain and install.
The second and most critical one is that the oven gases flux, when ascending in a closed environment (like my ‘tube’) tends to have a circular/helycoidal path. This means that all of volume of the chimney will be filled with the gases. And the ascending hot gases will warm up the surface of the chimney. Hottest the chimney, higher the suction.
By other way, circular path is a normal path to the gases flux. Square one will left cold points (corners) producing flux turbulence and etc.
Resuming, a hot cylindrical chimney will do suck all the lower gases to outer of the chimney and with a great volume by unit of time.
This is a good thing when the fire is beginning, the fresh air enter by the lowest side of the oven door, run all the dome ceiling and go out by the higher side of the oven door, giving a lot of oxygen to be combusted. The suction of the chimney collaborates to this air flux be big and uniform. (We are not considering the wood and cold oven spots/flux interference in this explanation)
At first moment the combustion is so big that, in my oven, part of the flux is not sucked by the chimney –bad sized- and goes out by the landing area.
When the fire is in ‘the heat regime’ there is an equilibrium between the btu´s that you need, the mass of the oven and the baking dough.
However, the chimney is still very hot, the flux by it is excellent and so the suction, wasting btu´s to free space.
There is when the damper is used.
We need the maximum of btu´s being used to heating the bricks and dough. We do not like wasted flux thru the chimney. OK?
To do this step easily, if you put your hand just outboard of the higher landing area with the damper opened, you could feel it a little warm. Closing slowly your damper will be easy to note when the gas flux begin to divide and going to the outer side of the landing area. Your hand will be blowing with hot gases.
Then, the only thing that you need is to re-open the damper a little to have the better relationship between suction and damping.
Or better, you could use your eyebrow to feel that
Any time the fire decreases the damper closes, and vice verse.
About the fire/smoke relationship, the answer is no, not always where there is fire there is smoke.
Smoke is seeing because the flux of gases passing thru the wood/charcoal are carry on the carbon residue. In the oven, the temperature of the combustion is so high, that this residue is combusted too, and so the residue of this residue, reaching the infrared paths of gases.
This last hot path is in the no visible part of the spectrum.
There your eyebrow is gone. As long as some nose hair too.

Let me know if I had answered your questions whit some coherence.
Luis
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Old 05-26-2006, 01:54 PM
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Default "fire decreases the damper closes, and vice verse."

(L) " Let me know if I had answered your questions whit some coherence.
Luis"

(M) Thanks, Luis for your explanation which I found coherent, but I will rephrase in case I get something wrong:

(M) The "bottom line" for me, if I understood correctly, is that we close the damper, not to lower the oxygen to the fire and reduce the flame size, but to prevent the heat from escaping up the chimney.

(M) This pizza oven chimney damper seems to be essentially different from how a damper works on an interior house heating oven. There, when I close the damper, because I restrict the exit of CO2, I will also choke the fire and cause it to burn more slowly and produce less heat.

(L) "By other way, circular path is a normal path to the gases flux. Square one will left cold points (corners) producing flux turbulence and etc."

(M) We generally use the word "flow" as you use "flux". I understood from my high-school physics and chemistry that a gas will take the shape of any container. If this is correct then a [] shape should produce no more turbulance than a 0 shape. Perhaps your specialty is in turbulance as I recall you warning me about a piece of angle iron producing resistance. I followed your advice and filled it with mortar.

(L) "At first moment the combustion is so big that, in my oven, part of the flux is not sucked by the chimney –bad sized- and goes out by the landing area."

(M) So, then I am not the only one who gets smoke in his face when starting my fire. I also used a round flue, and mine is also probably too small.

(L) " Any time the fire decreases the damper closes, and vice verse."

(M) So, I will try to apply that principle and hope that I don't choke my fire. Thanks for the detailed answer.

Obrigado,

Marcel
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