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  #21  
Old 01-28-2014, 11:09 PM
Peasant
 
Join Date: Oct 2013
Location: Hobart, Australia
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Default Re: 40" brick oven on Tasman Peninsula

G'day All,

Thanks again to everyone for your inputs so far. I was down there again this weekend. I spent most of Saturday chin scratching and naval gazing. Sunday I went for a bike ride (before the kids were out of bed). More hills, more thinking. In the end I decided to push on. I just couldn't bring myself to start tearing things down, or ripping the floor up. I will see it through as is and treat the whole thing as one big learning experience. At least by the time I build WFO #2 (which will possibly be where WFO #1 is currently standing) I will have more of an idea what I am doing, and also how the oven is functioning. i.e. if this one does turn out to be a dud, at least I will appreciate WFO #2 that much more for knowing the difference.

I have to confess the whole thermal mass thing I found quite confusing when I set out on this journey. The original plans I was using, and at least one other book I read, strongly suggested thermal mass was your best friend when building one of these. The consensus around FB seems to be the opposite. I suspect the difference might be between building a bread oven that cooks pizza, and a pizza oven that cooks bread? Our preference is really for the former, so part of me is still hopeful I might yet achieve that. If not though I am open (and expecting) to revisit at least the floor, if not the whole build, at a later date.

In the meantime once the decision was made, I got on and finished the dome. Unfortunately when tapping in the final cap a piece came off the inside of one of the bricks in the final row. It's not the prettiest inside dome I've seen, but it will do!

Andrew
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  #22  
Old 01-29-2014, 03:18 AM
Master Builder
 
Join Date: May 2011
Location: South Australia
Posts: 558
Default Re: 40" brick oven on Tasman Peninsula

Pushing on was the right decision, in my opinion.
A local hotel has a pizza oven in the beer garden.
It consists of a single central steel post with a sheet steel tray.
The floor bricks are laid straight on the steel tray. I imagine the heat loss would be rather phenomenal, straight through the brick and steel to the surrounding atmosphere. Probably a bit like your oven having more thermal mass than is optimal.
It has the flue in the main chamber. The dome is house bricks with a massive crack. I can stick my index finger in it, from the outside when it's cold, can only imagine how big it gets when it's hot.
The entry wouldn't be anywhere near 63% of the dome height, and its pretty wide too.
The dome is uninsulated.
Guess what?
This hotel has pizza nights, where it isn't unusual to serve a hundred ten dollar pizzas. All cooked in that oven in the beer garden and very nice to eat. They do take a little short cut. They buy caterer's packs of par-cooked bases that they just have to top, but they then have to cook them on trays to prevent the crusts over-cooking before the toppings cook. 4 minutes a pizza, 5 or 6 at a time, the boss reckons.
If that oven can do that, yours will certainly cook a few.
Given your floor has a lot of thermal mass soaking up the heat, you might want to try it out without dome insulation, this might restore some balance between dome and floor.

P.S. if the tank full of wood in the background is anything to go by, fuel use won't be a problem, eh?

Last edited by wotavidone; 01-29-2014 at 12:15 PM.
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  #23  
Old 01-29-2014, 04:52 AM
stonecutter's Avatar
Il Pizzaiolo
 
Join Date: Jun 2007
Location: South Carolina,USA
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Default Re: 40" brick oven on Tasman Peninsula

Just think of thermal mass as material that absorbs and stores heat. The more you have, the longer you need to fire it to saturate it.

The reason a ton of mass isn't embraced is because almost everyone here that builds an oven is a casual user, and they fire the oven occasionally. Unless you plan on baking commercial quantities of bread, an oven with a lot of mass is simply not needed. One that is heavy with mass really needs constant use to be practical, otherwise it becomes this fiddly, temperamental oven that requires all kinds of tricks....like using metal pan, par baked crust, uninsulated domes.....all that to accomplish what a lower mass, insulated oven can do without all the extra effort.

True, every project is a learning experience, now you can improve on he next one. The suggestion to omit insulation on the dome isn't a bad idea, though I wouldn't leave it off completely, that will make heating up even harder.
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  #24  
Old 01-29-2014, 05:02 AM
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Default Re: 40" brick oven on Tasman Peninsula

Quote:
Originally Posted by Blunt Tool View Post
G'day All,

Thanks again to everyone for your inputs so far. I was down there again this weekend. I spent most of Saturday chin scratching and naval gazing. Sunday I went for a bike ride (before the kids were out of bed). More hills, more thinking. In the end I decided to push on. I just couldn't bring myself to start tearing things down, or ripping the floor up. I will see it through as is and treat the whole thing as one big learning experience. At least by the time I build WFO #2 (which will possibly be where WFO #1 is currently standing) I will have more of an idea what I am doing, and also how the oven is functioning. i.e. if this one does turn out to be a dud, at least I will appreciate WFO #2 that much more for knowing the difference.

I have to confess the whole thermal mass thing I found quite confusing when I set out on this journey. The original plans I was using, and at least one other book I read, strongly suggested thermal mass was your best friend when building one of these. The consensus around FB seems to be the opposite. I suspect the difference might be between building a bread oven that cooks pizza, and a pizza oven that cooks bread? Our preference is really for the former, so part of me is still hopeful I might yet achieve that. If not though I am open (and expecting) to revisit at least the floor, if not the whole build, at a later date.

In the meantime once the decision was made, I got on and finished the dome. Unfortunately when tapping in the final cap a piece came off the inside of one of the bricks in the final row. It's not the prettiest inside dome I've seen, but it will do!

Andrew

To repeat, you don't need to destroy anything. The way your floor brick are oriented and set, you could pop the floor out, insulate and set splits over it in a day....in fact I bet it would take less than 4 hours.

I'm not trying to convince you of anything you don't want to do, but I think you have overthought the effort you need to put in to correct a simple problem.

Anyway, good work on the dome, they don't need to be pretty to work, and having tight brickwork makes no difference to what goes into the oven.
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  #25  
Old 01-29-2014, 03:09 PM
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Default Re: 40" brick oven on Tasman Peninsula

Hey Andrew - Learning is part of the job and what you learn will serve you well down the track. I reckon that you will be pleasantly surprised when you fire your oven up and sample the results.

Stonecutter has good advice with this. I would be shy about having no insulation on the dome for safety reasons alone.

There have been some builds documented here that are little short of works of art and some not so much. The thing they have in common is that they all work.

Congratulations on closing the dome and I wait with interest to see what comes out of it when you get going with fire.
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  #26  
Old 01-30-2014, 01:56 AM
Peasant
 
Join Date: Oct 2013
Location: Hobart, Australia
Posts: 33
Default Re: 40" brick oven on Tasman Peninsula

Thanks guys for your inputs, feedback and support.

Stonecutter - thanks for the explanation re thermal mass. It does clarify things a lot for me. I think you are also probably right about me over-thinking the floor. I have been accused of that in the past! In my deliberations on the weekend, I did realise that the dome I had built was already too high for me to reach the floor through the opening in the top. So even at that stage, to rip up the floor and add insulation would have to be done through the front opening. In that respect at least I haven't lost anything by closing the dome (although adding an entrance and flue might change that).

I do have more questions about thermal mass and insulation though, based on comments from Stonecutter and Greenman. I apologise for this, and hope I'm not pushing the friendship by asking too many, but unfortunately my brain is one of those models that has to know 'why' aswell as 'how'….

So thermal mass absorbs and stores heat. I'm OK with that. Let's say I insulated the dome to the maximum. When the heat passing through the firebricks in the dome reached the insulation, would it not then be reflected back into the oven (or at least a fair proportion of it), and as a result provide more heat to the thermal mass in the base? Would this then increase the rate at which this thermal mass reached saturation point, at least by comparison to a dome with no insulation?

Conversely if I were not to put any insulation at all over the dome, then once the bricks here were saturated any additional heat would be lost to the atmosphere. In this case, if I were prepared to lose this heat completely, then why not add more thermal mass to the dome and at least store that heat that would otherwise be lost? Over subsequent days wouldn't this then contribute to maintaining more heat in the oven for longer, which obviously wouldn't be enough to cook pizzas with but might help with cooking breads or other stuff?

Based on these two scenarios, with insulation at one end of the spectrum and more thermal mass at the other, putting nothing over the dome seems to be somewhere in the middle (and not achieving any of the potential benefits of either)?

Once again I hope I'm not being a pain here but I would appreciate further comment in helping me think this through.

Many thanks,

Andrew
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  #27  
Old 01-30-2014, 02:31 AM
Peasant
 
Join Date: Oct 2013
Location: Hobart, Australia
Posts: 33
Default Re: 40" brick oven on Tasman Peninsula

Quote:
Originally Posted by wotavidone View Post

P.S. if the tank full of wood in the background is anything to go by, fuel use won't be a problem, eh?
You're right there, fuel is one thing we have plenty of!
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  #28  
Old 01-30-2014, 02:42 AM
Master Builder
 
Join Date: May 2011
Location: South Australia
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Default Re: 40" brick oven on Tasman Peninsula

I only suggested you might want to try it without insulation based on the premise that the loss of heat from the dome to atmosphere might the large amount absorbed into the high mass floor. So the surface temperature of the dome bricks might more closely match the floor temperature. But both would be lower than that achievable in a fully insulated oven.

Pretty sure the bricks won't saturate, whatever that means, if the dome isn't insulated.

The "problem" here is simple. You have a high mass floor that is insulated underneath, and isolated from the block stand by being suspended. So while it's high mass, the losses to atmosphere might actually be rather low.
Other than that, its a pretty nice looking build.
So insulate the dome, add some extra mass if you want first, and accept that it will take a fair while to heat everything up.
Since you aren't exactly short of fire wood, I'm not entirely convinced you actually have a "problem".

Last edited by wotavidone; 01-30-2014 at 02:46 AM.
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  #29  
Old 01-30-2014, 04:37 AM
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Default Re: 40" brick oven on Tasman Peninsula

Quote:
Originally Posted by Blunt Tool View Post
So thermal mass absorbs and stores heat. I'm OK with that. Let's say I insulated the dome to the maximum. When the heat passing through the firebricks in the dome reached the insulation, would it not then be reflected back into the oven (or at least a fair proportion of it), and as a result provide more heat to the thermal mass in the base?
What insulation does is contain the heat within the mass. So, yes, once the mass has an equalized temperature from inside out, the convection action becomes more efficient from dome to floor. This is because the insulation has little to no thermal conductivity, which will trap the heat within the masonry.

Quote:
Originally Posted by Blunt Tool View Post
Would this then increase the rate at which this thermal mass reached saturation point, at least by comparison to a dome with no insulation?
Yes....an uninsulated dome loses the absorbed heat at a far greater rate than one with insulation. It's really that simple.

Quote:
Originally Posted by Blunt Tool View Post
Conversely if I were not to put any insulation at all over the dome, then once the bricks here were saturated any additional heat would be lost to the atmosphere. In this case, if I were prepared to lose this heat completely, then why not add more thermal mass to the dome and at least store that heat that would otherwise be lost?
Sure you could do that. But unless you add a significant amount of mass, the heat will be rapidly lost, once the radiant heat source is diminished.

But that is where you should start asking questions about what you want from an uninsulated oven performance wise. Do you want long extended firing sessions? How often will the oven be used?

Quote:
Originally Posted by Blunt Tool View Post
Over subsequent days wouldn't this then contribute to maintaining more heat in the oven for longer, which obviously wouldn't be enough to cook pizzas with but might help with cooking breads or other stuff?
Again, yes. But you can do that with 3"-5" of well insulated mass, without the extra long firing times and temperamental behavior of uninsulated masonry.


Quote:
Originally Posted by Blunt Tool View Post
Based on these two scenarios, with insulation at one end of the spectrum and more thermal mass at the other, putting nothing over the dome seems to be somewhere in the middle (and not achieving any of the potential benefits of either)?
No. All that does is contribute to the issue of inefficiency. Spend your time learning what kind of goodness you an make in your WFO, not how to balance out the heat. Just because you have an abundance of wood to burn, doesn't really mean an inefficent oven ( ie: uninsulate) is the right choice. To me, that's like saying you have a huge motor oil supply and your car that leaks a ton of oil is just fine.

Quote:
Originally Posted by Blunt Tool View Post
Once again I hope I'm not being a pain here but I would appreciate further comment in helping me think this through.
This is what a forum is for, IMO. Do not hesitate to ask questions....a good discussion helps everybody to push the bounties of what they know.

All that said, insulating the dome is less work than adding more thermal mass, and re-laying the floor is a minor fix. Obviously, the final decisions are yours, but the payoffs are significant.
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  #30  
Old 01-30-2014, 05:38 AM
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Default Re: 40" brick oven on Tasman Peninsula

Quote:
Originally Posted by wotavidone View Post

Pretty sure the bricks won't saturate, whatever that means, if the dome isn't insulated.
It's just nomenclature associated with heating the oven masonry. Saturation implys an even temperature throughout the thickness of the mass.
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