Driving heat across the cooking floor

[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

[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.

[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...

[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.

[david s]

Re: Driving heat across the cooking floor

People who are new to wood fired ovens always seem to be rather obsessed with reading temperature. After lots of firings your stopwatch hand and eye are enough. I always use the semolina on the floor trick (3 secs to turn black) to test floor temp. An infrared thermometer only reads the temp of the surface, so it has some limitations.

[GianniFocaccia]

Re: Driving heat across the cooking floor

Until I learn my oven I'm going wih the laser as well, but...

I could see the benefit of a thermocouple placed near the outside of the dome brick to indicate when the dome mass has been thoroughly saturated. With experience this should become intuitive but I'm sure thousands of ancient Italian housewives learned this without the convenience of a digital readout.
John

[david s]

Re: Driving heat across the cooking floor

with my oven I tell this by the slight warmth that makes its way down to the base of the dome. When this warmth has reached the base the oven is heat saturated and ready for pizza. A hand held to the outside can tell you lots.This method may not apply to those who have really well insulated ovens. If your oven is hot to the hand on the outside your insulation is damp.

[Les]

Re: Driving heat across the cooking floor

I could see the benefit of a thermocouple placed near the outside of the dome brick to indicate when the dome mass has been thoroughly saturated.

Gianni / David - I totally agree with you. But, When the oven goes white, you absolutely know the brick is saturated with heat. I never cook a thing until that event occurs. Then it's just a matter of letting things cool down and adjust to the temp you need. I'm not making a point for or against the toy's, it just never penciled out for me.

Brick - we seem to be on the same page

[david lyons]

Re: Driving heat across the cooking floor

Thanks all for the comments.

I take the point re "what is the point?", My thinking is that it is easy to make provision now and bloody hard later. Also I have a thermocouple I bought some time ago and I have to justify it don't I?

I'll go with the tube midway up and against the dome.

Dave Ly.

[david s]

Re: Driving heat across the cooking floor

"When the oven goes white, you absolutely know the brick is saturated with heat. I never cook a thing until that event occurs."

I guess we all do it a little differently. I often cook in my oven well before it goes white. If I'm doing a roast or bread I usually give the oven one hour of flame (this is where I use my stopwatch) which is usually enough for the top of the dome to begin going white and the rest still black. It is then enough to do the cooking. Faster that way and uses way less fuel. Using this method it's easy to cook a roast after work during the week. If I'm doing pizza for quite a crowd then I let my oven go completely white and about another 20 mins of flame before preparing the floor.If it's just for the family and we only want 3 or 4 pizzas I'll skip the extra 20 mins.

[Sharpshooter]

Re: Driving heat across the cooking floor

Great information, thanks. I ran into heat management issues on my first cook in my new oven. I didn't have a large enough fire going while cooking, so the floor temp dropped considerably. Next weekend I will try again, with a good fire going while cooking.

[texassourdough]

Re: Driving heat across the cooking floor

I haven't been following this thread but I think some recent comments deserve some qualification...for the definition of "saturated" that has been used is IMO misleading.

The normal definition of "saturated" would imply that the oven cannot store any more heat.

Having the oven go "white' does NOT mean the oven is saturated by any means. It means the surface is at 750 or so but doesn't tell you what the temp is at the far boundary of the refractory. For those with relatively thin, well insulated ovens the oven may well be approaching saturated but for those with heavier ovens the oven may be 2 or 3 hours or more from being even reasonably "heat saturated".

Barrel Vault ovens routinely heat for 3 to 4 hours before being used for bread baking and they will clear in an hour or so but are NOT heat saturated even at 4 hours. They need an hour or more to equalize and have the temps become more uniform through the refractory so that the stored heat will be available to reheat the oven as it cools from cooking/baking.

There is also a tendency in this list for people to confuse temperature with heat. Temperature is like pressure - it can be measured at a point. Temperature and pressure are properties and do not flow - though they do make things (like heat) flow. A match burns at about the same temp as a piece of wood. They have the "same" temp but they do not produce the same amount of heat. Heat is like water - it has a presence and can flow and be stored (in materials). A teaspoon of boiling water has the same temp as a gallon of boiling water but they contain differing amounts of heat. One has enough heat to cook something with the heat it contains the other does not. A just cleared WFO is much the same - it may be hot but it won't contain as much energy (stored heat) as it can.

Crawling off my stump and dodging the fruit and tomatoes!
Jay

[david s]

Re: Driving heat across the cooking floor

I totally agree Jay, but if I plan on only cooking two loaves of bread or a roast there is no need to heat saturate the oven and then let the temp drop. Why use up way more energy and time than you require. My oven in this case has usually only just gone white at the top half of the dome, nowhere near "saturation". If planning on cooking lots of bread or a large party of folk for pizza the regime is quite different and that's when you want plenty of stored heat in the oven.

[texassourdough]

Re: Driving heat across the cooking floor

Hi David! As you know, it is all part of "knowing" your oven! Sounds like you are doing a real short circuit of normal WFO practice, but...there are SO many variables that there are lots of odd combinations that work well for various purposes if you can find them!

[GianniFocaccia]

Re: Driving heat across the cooking floor

I totally agree Jay, but if I plan on only cooking two loaves of bread or a roast there is no need to heat saturate the oven and then let the temp drop

I totally agree with Jay's explanation of temperature vs heat and the analogy using water. One can cook a batch of pasta in a small volume of boiling water but it is generally agreed that the same pasta will cook to a better consistency in a large volume of boiling water. Just like heat-loading a WFO, it takes more energy to heat a large volume of boiling water than a small one. Jay, do you think a heat-saturated oven might behave in the same way? I would be tempted to cook a batch of bread like David in a partially-loaded oven if I wasn't planning on using it for the next few days.

John