Earthstone 110 or FGM?

[scott123]

Here is an updated schematic of the CF.  Looks like solid mass all the way up around the door opening:
http://person.smugmug.com/Hobbies/Outdoor-Kitchen/i-dgzSxJn/0/XL/110WoodTradSpecsPage2-XL.jpg
Although, these might not be super accurate as they state that the dome is 4" thick, but show the outside diameter at 49.5" and the interior as 44" [(49.5-44)/2=2.75" not 4", but the top of the dome appears to be thicker than the sides.

Actually, I was looking at the Neapolitan model and not the Traditional.

If you can afford a Ferrara and don't mind a long  pre-heat (most like a minimum of 8 hours for pizza), then I'd go with the Ferrara over the CF. Completely different league.

[scott123]

If one were to purchase an FGM "high" with the 12.8" dome and 11.5" door, would it be all that hard to build your own insert to lower the inner door height to 8.5"?  If you had such an insert, then you could have the best of both worlds.  11.5" door for the turkey, and use the insert when you want to cook neo pizza?  It's main goal would be to prevent the hotter higher air from escaping as easily, so it would only have to handle the heat.  Maybe make a metal band in the shape of the new inner door and top it with fire brick to the shape of the old inner door.  It would not have to be a perfect fit, just enough to block most air flow.

For those of you who are builders, could you not just mortar in an inner door solution as well?  Maybe support it with some thin pieces on the sides of the door to keep it in place and not lose too much width?

Yes, until Antoine comes up with a cast iron insert, I think a homegrown approach is an excellent idea.

I was thinking about this yesterday.  While it would be nice if the insert could be insulated and/or have some mass, neither are critical.  The main purpose is trapping hot air so that it contacts the dome longer before flowing under the inner door and up the chimney.  The lower the inner door, to a point, the more heat you're capturing in the dome. The higher the inner door, the more heat is lost up the chimney.

You might even be able to get away with something like copper flashing. You will want it to be fairly snug, though, so the gases are forced underneath it.

[Reep]

Actually, I was looking at the Neapolitan model and not the Traditional.

It doesn't appear that the Neapolitan model is made by CF.  I'm checking this to see who makes them.  FWIW, I saw in a video that Tony G's oven is the Traditional.

I'm still getting prices on a couple of fully completed ovens to see if I can get one close, but I think I could set up a FGM tall and find a way to get the internal door lowered.

[TXCraig1]

Yes, until Antoine comes up with a cast iron insert, I think a homegrown approach is an excellent idea.

I was thinking about this yesterday.  While it would be nice if the insert could be insulated and/or have some mass, neither are critical.  The main purpose is trapping hot air so that it contacts the dome longer before flowing under the inner door and up the chimney.  The lower the inner door, to a point, the more heat you're capturing in the dome. The higher the inner door, the more heat is lost up the chimney.

You might even be able to get away with something like copper flashing. You will want it to be fairly snug, though, so the gases are forced underneath it.

Scott, just thinking out loud here; how much difference could a couple inches of hot air make? Air doesn’t hold much heat. If you reduce the size of the door opening, you are also going to restrict the oxygen flow, right? I’d be more worried about the effect this had on the ability of the fire to convert fuel to heat. I would think a couple inches of hot air is a poor tradeoff for a cooler fire.

[Reep]

Scott, just thinking out loud here; how much difference could a couple inches of hot air make? Air doesn’t hold much heat. If you reduce the size of the door opening, you are also going to restrict the oxygen flow, right? I’d be more worried about the effect this had on the ability of the fire to convert fuel to heat. I would think a couple inches of hot air is a poor tradeoff for a cooler fire.

I think I may have a solution figure out.  I am going to talk to Antione about including an extra "insulated door" if I go with FGM.  The FGM insulated door fits inside the flush with the oven opening.  If I had an extra one of these I could cut an opening in it to 63% of the dome height and leave an inch or so of support on each side that would still allow pizzas up to 16" inches to pass through.  The insulated door is made to fit so this should be easy.  This way I could experiment with both openings.  If the restricted opening works, I can use it when cooking pizza and then remove it when i want to have a larger opening.  Best of both worlds.  Maybe FGM will manufacture it and call it a Reep Restrictor, or preferably something in French that sounds better.

[shuboyje]

Sounds like a great solution. 

[JConk007]

Kinda gotta go with Craig here. Scott I admire your research and number crunching but have you cooked in the FGM ? or the CF ?  Is there goto oven formula, ratio recipe you are striving for, and why again?  Homeowner specific.
I mentioned I have and did cook in the 950 and did not notice a loss in heat out the chimney? they have been making them this way for years and a lot of them ! aint broke dont fix it ! or rig it ! I am telling you in my rookie opinion these ovens Make a good neapolitan style  pizza ! Not a Stefano, but close to 1/2 the price all in right?
Thanks
John

[scott123]

John, I don't have to use an FGM or a CF to be able to understand the thermodynamics involved.  I've taken one of Jeff's diagrams and modified it to show what happens when the door is too high.

[scott123]

As you can see, when the door is too high, less of the superheated air is trapped in the dome. With less trapped superheated air, you get less heat transfer to the dome.  The lower the door, the longer you can keep the heat in the oven, the hotter the dome gets. We're not talking about a huge amount of time- the hot air might stay in the oven just a fraction of a second longer, but it's enough time for the exhaust gases on oven #1 (higher door) to be hotter than the the exhaust gases on oven #2.  Hotter exhaust gases translates into more heat loss on the high door. For the properly sized door you're talking about a faster pre-heat and a hotter dome overall.

Craig, since the door serves both the duties of exhaust and fresh air intake, you do have to be careful about how small you make the opening, but that's where the 63% ratio comes into play.  The Italians have been testing this for centuries and that's what they arrived at.  Like Jeff, I'm not in love with that exact figure, but I am head over heels for that realm- maybe 55%-70%, depending on the size of the oven, shape of the door and other factors.  Above 70%, though, and you're flushing wood down the drain.

Now, a high door, like a high ceiling, can definitely be worked around.  If you throw enough wood at it, it will get plenty hot.  But if a simple insert can make this oven more efficient (and I'll bet any amount of money it will), then I strongly feel that it's worth adding.

[Reep]

The challenge with using those diagrams is that they don't really accurately reflect the thermodynamics.  The air is obviously a continuum of temperatures, not quantum levels, and also the oven should be full of convection currents stirring the air, not to mention what happens when you move wood around or put a pizza in and out.

I don't disagree that a lower door might be important, but you would have to look at a lot more variables to scientifically come to that conclusion.  Maybe I will publish a paper in Pizza Science Magazine if I can get the Reep door to work.

[shuboyje]

The challenge with using those diagrams is that they don't really accurately reflect the thermodynamics.  The air is obviously a continuum of temperatures, not quantum levels, and also the oven should be full of convection currents stirring the air, not to mention what happens when you move wood around or put a pizza in and out.

I don't disagree that a lower door might be important, but you would have to look at a lot more variables to scientifically come to that conclusion.  Maybe I will publish a paper in Pizza Science Magazine if I can get the Reep door to work.

This is actually not true.  In a properly built oven the air is very stratified, you can actually visibly see it via smoke, and you can read it slightly with an IR thermometer and you move down from the peak of the dome.  It's all about density and the pressure differences it causes.  Inside the oven you have a huge pressure difference between the ambient outside air coming in to feed the fire and the hot gases coming off the fire.  These lead to a huge pressure differential between the two gases and a VERY stratified environment.

[TXCraig1]

Now, a high door, like a high ceiling, can definitely be worked around.  If you throw enough wood at it, it will get plenty hot.  

And you will have terribly unbalanced heat that will burn the edges of your pies.

I'm still unclear how a couple extra inches of hot air at the ceiling is going to make a meaningful difference?

The temperature of the dome itself and the height of the dome are what really matter, right? The power radiated from the dome is a 4^th order function of the temperature of the dome - for example, a 1200F dome would theoretically radiate more than 2X as much power as a 900F dome. Likewise, increasing the dome height decreases the view factor thus reducing the radiated power that strikes the pie. Compounding this, a high dome is harder to heat for the same reason. What role does the extra hot air play?

[shuboyje]

Have you ever cooked pizza in your oven without live fire Craig?  I understand the reasoning, and it is sound, but doesn't match what I have experienced in multiple ovens, I know we touched on this from a different angle in another thread.  Radiation off of the bricks doesn't have the power to cook the top of a pizza at neapolitan bake times, it's all about the convection.  Change the dynamics of the door and you change that convection.

Regardless of all the technical and theoretical stuff, the 950B works, and cooks a great Neapolitan pie from everything we have seen.  Added to that Antoine has offered a great solution for the case where the door height is an issue.  I think we are really talking about a moot point.

[TXCraig1]

Have you ever cooked pizza in your oven without live fire Craig?  I understand the reasoning, and it is sound, but doesn't match what I have experienced in multiple ovens, I know we touched on this from a different angle in another thread.  Radiation off of the bricks doesn't have the power to cook the top of a pizza at neapolitan bake times, it's all about the convection.  Change the dynamics of the door and you change that convection.

Regardless of all the technical and theoretical stuff, the 950B works, and cooks a great Neapolitan pie from everything we have seen.  Added to that Antoine has offered a great solution for the case where the door height is an issue.  I think we are really talking about a moot point.

That's where I was trying to get to - we know the 950B works. I think it is the low dome overriding other factors. 

I have cooked a pizza without live fire, and I don't like it. I don't however understand how does that relates to the issue at hand? The flames put off a lot of radiant energy, right? That's the difference between flames and no flames.

[Tscarborough]

I didn't read the whole thread, but Scott's diagrams are not correct.  There is no inversion layer trapping superheated air against the dome, the convection is visible in the oven in use and it sweeps the dome.  Any superheated air is below that in the center of the dome where a rolling cloud of smoke is visible if enough logs are added to create smoke.

[Reep]

Well, to partially close out this thread, I am scheduled to call Antoine tomorrow and discuss the options.  Either way it looks like I'm going with a 1500B (22-short) high (12.8" dome).  Thank you all for your valuable input.  It has been very helpful.

Rich

P.S. I start a new thread with pictures and progress of the construction.

[scott123]

I didn't read the whole thread, but Scott's diagrams are not correct.  There is no inversion layer trapping superheated air against the dome, the convection is visible in the oven in use and it sweeps the dome.  Any superheated air is below that in the center of the dome where a rolling cloud of smoke is visible if enough logs are added to create smoke.

Tom, the exhaust layer isn't trapping heat, it's the top of the dome that's trapping the heat as it rises. This really isn't all that complicated.  Hot air rises.  Cooler exhaust air sinks.  The rolling layer of smoke we've all seen at the door level is cooler then the air above it.

[scott123]

I'm still unclear how a couple extra inches of hot air at the ceiling is going to make a meaningful difference?

The temperature of the dome itself and the height of the dome are what really matter, right? The power radiated from the dome is a 4^th order function of the temperature of the dome - for example, a 1200F dome would theoretically radiate more than 2X as much power as a 900F dome. Likewise, increasing the dome height decreases the view factor thus reducing the radiated power that strikes the pie. Compounding this, a high dome is harder to heat for the same reason. What role does the extra hot air play?

The extra hot air makes for a hotter dome. It's kind of like when you pre-heat a home oven using the bake function and then turn the broiler on. The convective air rising from the bake element below pre-heats the ceiling of the oven, so that when you turn the broiler on, the top of the oven AND the broiler are radiating heat down.  Just like the active fire/red hot coals in a WFO are doing the lions share of the IR, the broiler element is doing the bulk of the work, but the air heated ceiling plays a part. In a WFO, where the ceiling has significant thermal mass, this role is even greater.

In a perfectly cylindrical 42" oven, a 2" lower door translates into 264 square inches of additional brick surface area contacting the hot air and 2772 cubic inches (19 cubic feet) of additional hot air volume.  That triples the volume of the 1" head space created by the original door.  And that's with a perfect cylinder.  With a rounded dome, that 1" of head space with the original door could be 1/5 to 1/6 of the head space with the 2" lower door. 5 times more volume translates into 5 times the space for superheated air.

[Reep]

The extra hot air makes for a hotter dome. It's kind of like when you pre-heat a home oven using the bake function and then turn the broiler on. The convective air rising from the bake element below pre-heats the ceiling of the oven, so that when you turn the broiler on, the top of the oven AND the broiler are radiating heat down.  Just like the active fire/red hot coals in a WFO are doing the lions share of the IR, the broiler element is doing the bulk of the work, but the air heated ceiling plays a part. In a WFO, where the ceiling has significant thermal mass, this role is even greater.

In a perfectly cylindrical 42" oven, a 2" lower door translates into 264 square inches of additional brick surface area contacting the hot air and 2772 cubic inches (19 cubic feet) of additional hot air volume.  That triples the volume of the 1" head space created by the original door.  And that's with a perfect cylinder.  With a rounded dome, that 1" of head space with the original door could be 1/5 to 1/6 of the head space with the 2" lower door. 5 times more volume translates into 5 times the space for superheated air.

If that is true, and the primary factor, then should it take 5-6x as long for an FGM oven to heat up, and 5-6x the amount of fuel to keep it hot?  This isn't the case according to those who have used both door heights.  I think there are many more factors involved than just the hot air trapped above the door.

Also, remember that you can only count the dome space in the vicinity of the door, not the back of the oven.  Otherwise you could argue that a 1-inch wide and 16-inch high door on a 16-inch dome oven would not retain any heat, which isn't the case either.

[scott123]

If that is true, and the primary factor, then should it take 5-6x as long for an FGM oven to heat up, and 5-6x the amount of fuel to keep it hot?  This isn't the case according to those who have used both door heights.  I think there are many more factors involved than just the hot air trapped above the door.

I didn't say that hot air volume was a primary factor in pre-heating and high temperature maintenance.  It is a contributing factor.