How long to preheat a Pompeii pizza oven?

[Timothy_W]

It takes a long long time and many fires to drive water out of the wet floor insulation (as you said, it got very wet), especially once the floor bricks are placed on top. With wet or damp insulation, you will see the heat from the floor bricks transmit fairly readily down to the hearth, just give it some time, each firing will get better.

That's for sure. After all, the oven is tempered in its own way during baking. Of course, this does not apply to metal stoves. But about brick, cement and clay, that's true.

[UtahBeehiver]

It takes a long long time and many fires to drive water out of the wet floor insulation (as you said, it got very wet), especially once the floor bricks are placed on top. With wet or damp insulation, you will see the heat from the floor bricks transmit fairly readily down to the hearth, just give it some time, each firing will get better.

[danhem]

mefornaio Many thanks for your explanation as above. I think you are right, I am probably not using enough wood.

I did a 4 hour burn and got more heat into the oven than ever before. From that burn we threw out 14 pizza in around 40 mins with a live flame burning. The oven floor temp reduced to around 600f after the last pizza was cooked. I would have need to recharge the floor if I need to cook more as they pizzas were taking longer to cook towards the end of the 40 mins.

I am still scratching my head over the heat drain under the hearth floor though. Drain outside of the dome is minimal, but with an ambient temperature of around 90f under the oven, after the 4 hour fire, the temperature under the hearth was at around 130f. This has been consistent since I've been burning fires to max temperatures.

My build process was followed the recommend cement hearth (with 5 weep holes drilled), 2" ceramic fibre board then the oven floor. I am wondering if I have not laid enough ceramic fibre board insulation under the oven floor bricks and that this is the reason why my floor will does not retain heat as efficiently as it could? The plans did state that 2 inches should be sufficient, as have many other posts, but I can understand why I'm having this heat drain issue.

I do know that the ceramic fibre board got very wet during a downpour as my protective canopy was ripped to pieces by the storm, but this is sometime ago now and I've had a lot of fires producing exactly the same result - ambient temp of 90f, spiking to 130f under the hearth. Incidentally, the following morning the under hearth temp is still 130f.

I'm hoping that patience will be my friend here and that over time, somehow the floor will become more efficient.

Thanks again,

Danny.

[MarkJerling]

The above is a direct quote and the (I&#827) just appeared like a few other oddities in my last few posts so I have no idea what is going on.

Back to the issue. 3 HOURS should be MORE than sufficient for your needs at this point. Re reading one of your statements you say your 3 hour burn produced enough heat for 4-6 pizzas. Im not sure if I'm missed something or what but I don't even see how this is possible. You are cooking the pizzas with a live fire in the chamber are you not?

"I have been basically setting a stack alight and adding logs every 10/15 mins until the carbon clears" is this taking 3 hours? You need to be more descriptive of your specific procedure. I am not sure what the general consensus here is but I have never followed anything to the letter with these types of ovens. Its a constant changing process that although there are some general guidelines that apply loosely trying to follow others is a recipe for more frustration.

Clearing the dome in my opinion is not the "pop up turkey timer" MY oven is not done when the dome clears by any means. I took a look real quick at your profile and see that your oven is a 36"er. Our mobile is the same size and I'm telling you now 3 hours even with the crappy wood I mentioned before is more that sufficient for a full charge.

We use that oven for the Farmers Market on Sundays. There we do around 150 - 200 pizzas out of that oven. I heat the oven for approx 2.5 hours 3 ideally but not necessary. Since your having wood issues im going to use the crappy wood i mentioned as the basis for this. For the entire day I used about a wheelbarrow full of that crap wood, I don't know each bundles amount (pretty standard here in the US so someone might have to chime in as to what it is) but I was getting 5 or 6 and that was just about right on the money and lasted the 5 hours.

I usually started the fire around 6/6:30 or 7 am and at 9 am we are ready to roll MOST times sometimes the wood just is took weak and needs about a half hour more, but as a general rule that 2.5 hours works. I am not positive but I believe I was using at least 2 possibly more bundles to charge the oven initially. That woods BTUS were very low we run the oven on that day at 925-950 or more at times because of the volume and my dough, all things considered those are the numbers that work for my operation. We are getting a full bake (12"/ 230-240g) in about 75 seconds at peak times, again, were were achieving this with that crappy wood as well.


My firing procedure is to build a stack in the center (left to right) of the oven and just forward of the center front to back. So the back side of my stack is inline with the center of the dome (approx)

I light this and when it has burned down to the lower logs and going good I will start adding wood to the left, right (and center if necessary) of it about 3 pieces (2-3" diameter) on both sides. I like to let this get really fully engulfed and start to die back before adding any more wood to the sides and middle.

When I started cooking with retained heat I would stock the oven (a barrel vault bread oven) and let it burn from front to back and add wood from back to front for the second round. I find that is a little to harsh for my pizza ovens and I fire it from front to back, again this is what works for me.

As it burns towards the back almost the entire floor width is in contact with wood, embers or flame as well as the dome and sides fire is touching everywhere except a small space on the hearth slightly back below the throat ..As it burns down I add more to the sides, middle and this process continues till it burns all the way to the back wall. The dome has cleared a bit ago and the oven is STILL not ready yet for the day (for MY needs)

I do not have any thermal couples nor do I use my IR gun during this process. The only time I use the IR gun is to show a doubting customer that doesn't believe we can cook in a 950 oven (usually I will give them a dome shot that's about 11-1200 and they gasp and ultimately shut up. This is what I mean by getting to know YOUR oven you certainly an use the thermal couples and the gun to help the process and it truly does help but ultimately it will be something you come to just know and feel.

So after the last bit of wood is added I will try>>>TRY>>> to let the oven soak for a bit (about 20 min works great) by raking the coals over the entirety of the oven floor WITH THE DOOR OFF. I say the door off for me because some douchebag stole the one I built years ago and I have never made another one so I don't use one. I point out the no door because I want you to see that even with NO door for the soak it still works. After the soak I clean up the hearth and rake the coals to one side and add logs for a live fire to start cooking.

Keep in mind ALL of this changes to some degree with each batch of wood no matter WHAT quality it is. It can be all oak but some will be older that others or have retained a bit more moisture or be more dense or a multitude of different wood related issues. The ambient temperature also effects the oven. Believe it or not when its 115 here the oven is MORE difficult to heat up than say our winter or fall temps of about 40-50 in the early am

I could go on but I have a sneaky suspicion that you are not using enough wood or you fires are not hot enough is the issue not so much the length of time based on your wood and fire comments I just read.

Great explanation, thanks! I did have a good chuckle when I got to the part about the door!

[MarkJerling]

The wife seems to think that it’s an expensive wood. Seems that there may be a wood called mai khaen hua that would be more affordable for burning. I’ll ask my supplier if she can get some.

thanks for the tip

Yes, that will work well too.

[mefornaio]

Appreciate the motivational speech. This weekend will be a real test of the oven. A long slow fire is planned so I’m pretty confident that the oven will perform.

cheers.

The above is a direct quote and the (I&#827) just appeared like a few other oddities in my last few posts so I have no idea what is going on.

Back to the issue. 3 HOURS should be MORE than sufficient for your needs at this point. Re reading one of your statements you say your 3 hour burn produced enough heat for 4-6 pizzas. Im not sure if I'm missed something or what but I don't even see how this is possible. You are cooking the pizzas with a live fire in the chamber are you not?

"I have been basically setting a stack alight and adding logs every 10/15 mins until the carbon clears" is this taking 3 hours? You need to be more descriptive of your specific procedure. I am not sure what the general consensus here is but I have never followed anything to the letter with these types of ovens. Its a constant changing process that although there are some general guidelines that apply loosely trying to follow others is a recipe for more frustration.

Clearing the dome in my opinion is not the "pop up turkey timer" MY oven is not done when the dome clears by any means. I took a look real quick at your profile and see that your oven is a 36"er. Our mobile is the same size and I'm telling you now 3 hours even with the crappy wood I mentioned before is more that sufficient for a full charge.

We use that oven for the Farmers Market on Sundays. There we do around 150 - 200 pizzas out of that oven. I heat the oven for approx 2.5 hours 3 ideally but not necessary. Since your having wood issues im going to use the crappy wood i mentioned as the basis for this. For the entire day I used about a wheelbarrow full of that crap wood, I don't know each bundles amount (pretty standard here in the US so someone might have to chime in as to what it is) but I was getting 5 or 6 and that was just about right on the money and lasted the 5 hours.

I usually started the fire around 6/6:30 or 7 am and at 9 am we are ready to roll MOST times sometimes the wood just is took weak and needs about a half hour more, but as a general rule that 2.5 hours works. I am not positive but I believe I was using at least 2 possibly more bundles to charge the oven initially. That woods BTUS were very low we run the oven on that day at 925-950 or more at times because of the volume and my dough, all things considered those are the numbers that work for my operation. We are getting a full bake (12"/ 230-240g) in about 75 seconds at peak times, again, were were achieving this with that crappy wood as well.


My firing procedure is to build a stack in the center (left to right) of the oven and just forward of the center front to back. So the back side of my stack is inline with the center of the dome (approx)

I light this and when it has burned down to the lower logs and going good I will start adding wood to the left, right (and center if necessary) of it about 3 pieces (2-3" diameter) on both sides. I like to let this get really fully engulfed and start to die back before adding any more wood to the sides and middle.

When I started cooking with retained heat I would stock the oven (a barrel vault bread oven) and let it burn from front to back and add wood from back to front for the second round. I find that is a little to harsh for my pizza ovens and I fire it from front to back, again this is what works for me.

As it burns towards the back almost the entire floor width is in contact with wood, embers or flame as well as the dome and sides fire is touching everywhere except a small space on the hearth slightly back below the throat ..As it burns down I add more to the sides, middle and this process continues till it burns all the way to the back wall. The dome has cleared a bit ago and the oven is STILL not ready yet for the day (for MY needs)

I do not have any thermal couples nor do I use my IR gun during this process. The only time I use the IR gun is to show a doubting customer that doesn't believe we can cook in a 950 oven (usually I will give them a dome shot that's about 11-1200 and they gasp and ultimately shut up. This is what I mean by getting to know YOUR oven you certainly an use the thermal couples and the gun to help the process and it truly does help but ultimately it will be something you come to just know and feel.

So after the last bit of wood is added I will try>>>TRY>>> to let the oven soak for a bit (about 20 min works great) by raking the coals over the entirety of the oven floor WITH THE DOOR OFF. I say the door off for me because some douchebag stole the one I built years ago and I have never made another one so I don't use one. I point out the no door because I want you to see that even with NO door for the soak it still works. After the soak I clean up the hearth and rake the coals to one side and add logs for a live fire to start cooking.

Keep in mind ALL of this changes to some degree with each batch of wood no matter WHAT quality it is. It can be all oak but some will be older that others or have retained a bit more moisture or be more dense or a multitude of different wood related issues. The ambient temperature also effects the oven. Believe it or not when its 115 here the oven is MORE difficult to heat up than say our winter or fall temps of about 40-50 in the early am

I could go on but I have a sneaky suspicion that you are not using enough wood or you fires are not hot enough is the issue not so much the length of time based on your wood and fire comments I just read.

[danhem]

You already said it.

"if building the oven was a learning curve l, the actual fire and heat management is also something that needs time to master."

I can assure you it's not the wood. As a general rule we use oak and citrus or Almond and oak or citrus for our mobile. For a period of about 6 monts last year I was running exclusively the crap from the grocery store (some kind of nasty pine mix) Sure I had issues with it but honestly once you get to know your oven through repeated and frequent usage you'll get the hang of it. There really is no substitute for this method.

Just keep at it it will come.

Appreciate the motivational speech. This weekend will be a real test of the oven. A long slow fire is planned so I’m pretty confident that the oven will perform.

cheers.

[danhem]

Can you get mai khaen? I understand that should work well.

The wife seems to think that it’s an expensive wood. Seems that there may be a wood called mai khaen hua that would be more affordable for burning. I’ll ask my supplier if she can get some.

thanks for the tip

[mefornaio]

You already said it.

"if building the oven was a learning curve l, the actual fire and heat management is also something that needs time to master."

I can assure you it's not the wood. As a general rule we use oak and citrus or Almond and oak or citrus for our mobile. For a period of about 6 monts last year I was running exclusively the crap from the grocery store (some kind of nasty pine mix) Sure I had issues with it but honestly once you get to know your oven through repeated and frequent usage you'll get the hang of it. There really is no substitute for this method.

Just keep at it it will come.

[MarkJerling]

I think I need to burn a fire longer. I have been basically setting a stack alight and adding logs every 10/15 mins until the carbon clears. I think my longest fire has been 3 hours, which so far has delivered a heat profile suitable for 4-6 Pizzas. Sealed over night with a door from there the oven does retain heat quite well.

we have 20 friends coming next week so I’ll plan for a longer fire and hope that the floor soaks up more of the heat.

if building the oven was a learning curve l, the actual fire and heat management is also something that needs time to master.

Im not 100% happy with the wood I’m using for fuel. Seems that quality hardwood available in the West isn’t available here. All the pizza restaurants use a variety of Pine. It’s a hard wood with no sap residue. My source of wood is dry but it burns through very quickly so I’m not sure how much heat it is actually giving off, but at I guess I need to work with Whats available here in Thailand.

Can you get mai khaen? I understand that should work well.

[danhem]

I think I need to burn a fire longer. I have been basically setting a stack alight and adding logs every 10/15 mins until the carbon clears. I think my longest fire has been 3 hours, which so far has delivered a heat profile suitable for 4-6 Pizzas. Sealed over night with a door from there the oven does retain heat quite well.

we have 20 friends coming next week so I’ll plan for a longer fire and hope that the floor soaks up more of the heat.

if building the oven was a learning curve l, the actual fire and heat management is also something that needs time to master.

Im not 100% happy with the wood I’m using for fuel. Seems that quality hardwood available in the West isn’t available here. All the pizza restaurants use a variety of Pine. It’s a hard wood with no sap residue. My source of wood is dry but it burns through very quickly so I’m not sure how much heat it is actually giving off, but at I guess I need to work with Whats available here in Thailand.

[mefornaio]

Ok thanks for the info, very interesting.

I think like you, my issue is in heating up the floor sufficient to saturate. I’m pretty happy with how the oven retains heat for 48 hours after a pizza cook - with the door in overnight I can bake bread the following morning, roast meat during the afternoon and cook ribs the following day after that.

my floor bricks are 2.5’’, during a fire zero heat comes through the hearth - however the following morning heat through the hearth spikes/drains by around 30f and this has been constant for some time now. I find it strange that during the entirety of a fire the underfloor records zero heat drain, yet overnight (woth oven door tightly fitted) heat begins to drain through the bricks, ceramic fiber board and concrete.

id be really quite pleased with my oven’s performance if I could figure the floor issue out. I’m hoping your longer and slower fire method is the key to a better floor performance.

You don't mention your current firing method but if you are not seeing any hearth absorption something is wrong. A 200° drop in how much time? Your hearth bricks should be saturated at the end of the fire up or at least 75%

Raking the coals over the hearth is an excellent practice to equalize the floor and achieve a deep charge. Your might need to extend the soak or perhaps increase the footprint of the fire rather than its volume, if that makes sense. What I mean by foot print is have as much floor real estate in contact with embers during your firing process and not just a fire say in the middle or off to the side.

As I charge my mobile oven 36" at the half way point my entire hearth is covered and remains that way till near the end. The inherent problem with operating one of these oven on a part time basis is the multitude of variables. Prior to the pandemic we were in operation for 4 days a week and even at this interval for over 5 years now the oven has its own ways.

Moisture in the board is EXTREMELY difficult to drive out. I would suggest doing a series of fires over about a weeks time and installing the door after each one. Before I put trim on my deck we had some water infiltration and I swear I could feel its presents even at 4 days a week for a good 2 weeks.

A longer slower burn to a point always will give you a deeper and more even charge to the oven overall. There is a balance unique to YOUR individual oven you just need to find by usage.

[MarkJerling]

Ok thanks for the info, very interesting.

I think like you, my issue is in heating up the floor sufficient to saturate. I’m pretty happy with how the oven retains heat for 48 hours after a pizza cook - with the door in overnight I can bake bread the following morning, roast meat during the afternoon and cook ribs the following day after that.

my floor bricks are 2.5’’, during a fire zero heat comes through the hearth - however the following morning heat through the hearth spikes/drains by around 30f and this has been constant for some time now. I find it strange that during the entirety of a fire the underfloor records zero heat drain, yet overnight (woth oven door tightly fitted) heat begins to drain through the bricks, ceramic fiber board and concrete.

id be really quite pleased with my oven’s performance if I could figure the floor issue out. I’m hoping your longer and slower fire method is the key to a better floor performance.

I'm finding heat retention, with the door fitted, is very good. I fired it up on Friday and it took until Tuesday midday for the temperature to drop back to ambient. I've also checked my floor slab and that does not heat up at all, so I'm confident that my underfloor insulation is working well. I'll try a longer fire next time and see what happens. I wish I had thought of putting a heat sensor under the floor!

Here's the revised heat profile with the door fitted:

[danhem]

Ok thanks for the info, very interesting.

I think like you, my issue is in heating up the floor sufficient to saturate. I’m pretty happy with how the oven retains heat for 48 hours after a pizza cook - with the door in overnight I can bake bread the following morning, roast meat during the afternoon and cook ribs the following day after that.

my floor bricks are 2.5’’, during a fire zero heat comes through the hearth - however the following morning heat through the hearth spikes/drains by around 30f and this has been constant for some time now. I find it strange that during the entirety of a fire the underfloor records zero heat drain, yet overnight (woth oven door tightly fitted) heat begins to drain through the bricks, ceramic fiber board and concrete.

id be really quite pleased with my oven’s performance if I could figure the floor issue out. I’m hoping your longer and slower fire method is the key to a better floor performance.

[MarkJerling]

When you say ‘smaller fire’, how long would you say it takes for the dome to clear?

working on fire management at the moment and whilst I can get to pizza temp in a couple of hours, I can feel that the oven isn’t fully saturated and that i’d struggle to throw out any more than 6 pizzas. My dome clears after 90 mins.

I’m not so worried about heat sink - I see zero spike in temperature through the hearth floor and dome.

I guess my real concern is the oven floor. After a strong fire I’ll let the embers sit on the floor for 20 mins or so. After clearing the floor for pizza space, the floor temp drops from 850f to 650f pretty quickly. In an ideal world I’d like to maintain the floor at 750f for a sustained period.

I have 2.5” ceramic fiber board under the floor bricks and as said above, it doesn’t register an external heat sink until the following morning (where I see the temp spike by around 30f).

in this case I can only conclude that I haven’t saturated the floor with enough heat. I have been concerned about damp insulation but I’m around 20 full blown fires in now so assume that any damp has been driven out.

I'd say the dome clears in about 2 hours, but my oven needs more time to fully saturate the dome. Once that happens, the dome holds the heat well. I find that my floor cools too quickly for my liking and I suspect that's because I used 45mm (1.75") thick fire bricks for the floor. I could pull them out (they're set on sand) and add another layer underneath but I think I'll just keep it as it is for now so as to get a better idea about the temperature profile.

If I try to heat the oven with a big fire over a short period, then the dome gets to about 950F and the floor gets to 800F but drops off pretty quickly. In one hour, the dome is at 900F and the floor at 730F. That's fine for my use, but after that, the dome drops to 700F after 2 hours and the floor to 580F, which is fine for the dome, but a bit cool for the floor in my view.

With a longer but somewhat smaller fire, I get the dome to around 1050F and the floor to 960F in just under 4 hours. I've not yet tested to see what would happen if a build a bigger fire for 4 hours, or built a fire for longer. An hour after raking the coals and clearing the floor the dome drops to 910F and the floor to 730F, which is almost identical to the shorter heating period, but after that, at the 2 hour mark, the dome is still 890F and the floor 650F. So, on that basis, it seems unlikely that I'll be able to keep the floor hotter, unless I add more thermal mass, but time and practice will tell!

But, at least the insulation seems to be working because at the 3 hour mark, the dome is still 825F and the floor 625F. After 4 hours, the dome is at 716F and the floor at 618F. Because my oven's floor is 42" diameter, I can cook 3 large pizzas easily at one time, but I find it's most practical to only do two at a time, adding one to the rear after rotating the other and moving it to the side. I have not yet tried to do more than 12 pizzas directly after each other so it's hard to say how much heat is lost each time I add a fresh pizza. Also, I've found that adding a small log to the coals from time to time helps.