Forno Bravo Forum: The Wood-Fired Oven Community

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-   -   Can't get to "Pizza Hot" (http://www.fornobravo.com/forum/f17/cant-get-pizza-hot-12404.html)

lwood 03-26-2010 06:13 PM

Can't get to "Pizza Hot"
 
I am new to this heat management stuff so I'm sure I haven't tried everything, but I haven't been able to get much over 550 F. My Oven is 60 inches dia with 4" of unexpanded perlite. I have fired it up with what I would consider a medium to large fire with flames lapping up to the top of the dome. It takes about 2 hrs to get it nice and hot. Most of the time I have the door closed during heat-up. Having the door open keeps the flames going. Am wondering if I should keep the door open during heat-up. This seems counter productive. The door is a loosely fitting piece of metal plate which gets very hot, pot holder hot. The dome gets slightly warm to the touch, less than 150 F. I haven't really fired it up to a roaring fire yet so I guess that's the next step. How long should it take to get to temp? Also I am just measuring with an oven thermometer that only goes to 600 F. Never got the entire dome white hot. Any suggestions are certainly appreciated.

RTflorida 03-26-2010 08:17 PM

Re: Can't get to "Pizza Hot"
 
Fire needs oxygen, putting the door in place during heat up starves the fire - no big fire, no heat. The only time you should be using a door is with the fire and coals removed for extended baking (roasting, baking bread, and such), or you can leave some coals in, throw in some wood chips and put the door in place for smoking.

Flames just lapping the top of the dome isn't a big enough fire in my book. You need a big fire - flames rolling and swirling in the top of the dome. There are quite a few example photos in this forum. One of our senior and VERY knowledgeable members Canukjim coined the phrase "plasma effect" and posted several very good photos.

Even a well insulated 60" oven is going to have a long heat up - a lot of mass to get hot. 4" of insulation would be deemed as adequate, more is always better. I'm guessing with a big fire, such as I've described, will take somewhere around 3-4 hrs to burn white.
You make no mention of hearth insulation (under the oven floor). Please tell us you have at least 4" of perlcrete or some other suitable insulation under there.

RT

splatgirl 03-26-2010 08:20 PM

Re: Can't get to "Pizza Hot"
 
That is a HUGE oven.
What is it built from? Is there insulation on the dome?
A "big fire" for my 36" during heat up is basically filling the entire dome with fire and flames. The active fire takes up most of the floor space and I try and keep it close to that large for 1.5 hours, at which point I am usually in the 800-900F range and dome is white.
The fire will need adequate air supply to burn hot enough. At most, I use my door as a wind block in front of the outer arch. I never close up the opening during active pre-heat firing as it kills or limits the combustion.
I can't imagine how many pieces of wood it would take to get this same volume of fire in a 60" oven, but it would be a LOT. Like a lot lot.

backinoz 03-27-2010 03:04 AM

Re: Can't get to "Pizza Hot"
 
60" that a community asset. Are you refering to inside or outside dia. the standard is to ref the inside dia of the dome.
I have a ~42" that takes 2hrs 20 to get to cooking temp.
For a nights cooking it consumes about 3 sections of log about 12 inches in diameter and 12" long. This includes keeping the fire going during cooking.
For me the key to determining how hot to go before you start to cook is on the color of the dome. When the fire is started it creates some smoke/soot that turns the bricks in the dome black from the top of the first soldier course to the top. After about 1hr 50 with a reasonable fire the soot on the very top inside of the dome goes clear (or disappears) over time this continues until it gets to the bottom of the dome.

On my oven I also monitor the color of the dome arch support bricks. these are subject to the heat from the fire but also the cooling that happens in the arch. When the soot turns clear at the level of the arch you can see that it is only to that temp on the surface. Over time the soot turns clear towards the arch exit. For me this is an indication when the back of the brick is at temp and is an indication how much heat is stored in the oven

In terms of the door as long as their is a sufficient gap it should be ok. I had a well sealing door at the start of my adventure and when i put in on you could see the fire start to starve and smoke. The door I use now has about an inch gap at the top and a couple of vents at the bottom that allow air in. I position it at the entrance so it doesnt impact the chimney draft.

Best of luck. At the end of the day light the fire and watch, have a few beers and see how it changes. Once you have dried out your oven in the first dozen fires you shouldn't need to worry about getting your oven to hot. Most medium Alumina fire bricks have a service temp above 1000oC.

lwood 03-27-2010 03:27 AM

Re: Can't get to "Pizza Hot"
 
Thanks for all the input. Yes I have 4" of perlite under the hearth and the oven is 60" inside diameter. Am beginning to think that was a little too big, it's ok I have lots of firewood. Ha ha. Learned a lot from your comments. The door I think is the biggest problem and time. I think I have been starving the fire and not letting it go for long enough to get hot. Going to give it a try tomorrow. Thanks again for all your comments.
John

texassourdough 03-27-2010 07:13 AM

Re: Can't get to "Pizza Hot"
 
Hi John!

You don't mention any insulation on the outside - though your external temp suggests there is.

I think you are suffering from several problems. First, toss the door UNLESS you are baking with NO FIRE in the oven (i.e. after the oven is hot).

Second, you want a BIG FIRE. I usually have flames coming out the door of my oven during the heating period - not necessarily once the fire gets pushed all the way to the back but... BIG FIRE! My oven clears in 45 minutes and is ready for pizza in an hour. Size has little to do with how long it takes - it is more about fire size, insulation, oven wetness, and oven configuration (which can cause problems it is way wrong).

Second, you are underinsulated (but this is a secondary issue - even a leaky oven can reach good temperatures). My dome NEVER gets to 110 except when the sun is hot - even after hours of firing. It sounds like you are probably losing a lot of heat through the dome. Without knowledge of how the hearth is configured it may be okay - maybe not.

Good Luck!
Jay

lwood 03-27-2010 04:00 PM

Re: Can't get to "Pizza Hot"
 
Thanks Jay, that makes a lot of sense. I do have about 4 inches of unexpanded perlite on the outside dome. Always thought that I may not be enough. That's one of the reasons I why I haven't rendered it yet. I think I've decided to add a few more inches of perlite/concrete to the dome and build it up more around the flue. Will post pics

lwood 03-27-2010 04:22 PM

Re: Can't get to "Pizza Hot"
 
1 Attachment(s)
Here is the oven, I have thrown away the door (for now). My question is should I also cover the brick entry archway with perlcrete and add maybe 2-4 inches additional percrete to the whole dome. What do you think?

DrakeRemoray 03-27-2010 05:38 PM

Re: Can't get to "Pizza Hot"
 
That is a nice looking oven.

I am a little concerned over the term unexpanded perlite. Why "unexpanded"? I am not SURE that it matters, but the stuff I used was very light and a quick google search makes me think it was expanded...

I really think that your problem is just having bigger fires and getting all the moisture out of the oven. It takes quite a few firings before it is really dry.

Drake

texassourdough 03-27-2010 06:09 PM

Re: Can't get to "Pizza Hot"
 
Hi John...

IF your oven is new you may still be fighting water. (or if your oven absorbs rain!)

I agree with Drake, good looking oven. I wouldn't worry about adding any insulation until you know more about your oven.

One point for you to consider. My oven is about 40 inches in diameter. Yours is 60 which means your floor is twice as big and (assuming similar thickness/mass) has twice as much cement/brick to heat up. IF you were to buld my fire (which pretty much fills up my oven) it would take about twice as long to reach temperature. Given your comments I am willing to guess your fire is somewhat smaller than mine. Be agressive and build bigger fires! You will need a formidable fire even once you are at temperature to keep that big oven hot!

Good Luck and let us know how it all works!
Jay


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