#1  
Old 11-23-2009, 04:30 PM
Serf
 
Join Date: Nov 2009
Location: Australia, Melbourne
Posts: 20
Default Oven height

Hi all, I'm new to all this WFO business and am having a little trouble reaching and maintaining oven temp. My suspicion is that the interior height is too high, and doesn't allow enough reflected heat to reach the floor, or the door opening is too high and lets out too much heat. I have attached a photo with dimensions, I am wondering if anyone can see any glaring problems here.

Interior Height - 22 inches
Interior width - 29 inches
Interior Depth 27 inches
Door Height - 19 inches

I would appreciate any help or comments.
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Oven height-img_0030.jpg  
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  #2  
Old 11-24-2009, 09:53 AM
eprante's Avatar
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Location: El Cajon CA
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Default Re: Oven height

Enzo,

I am in the process of building my oven (Eric's WFO build), but from my reading and research your concerns are right on. Your door height should should only be 63% of oven height. The other thing that may be limiting you from reaching temp is insulation. Both the door height and insulation can be modified ( though it may not be as elegant as your current brick arch entry)
Good luck
Eric

Last edited by eprante; 11-25-2009 at 07:42 PM. Reason: spelling errors-vanity
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  #3  
Old 11-24-2009, 12:57 PM
Serf
 
Join Date: Nov 2009
Location: Australia, Melbourne
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Default Re: Oven height

Thanks Eric, I think my insulation is pretty good, I have several layers of Shiralite mix plus 2 woolen insulation blankets and mortar render on top. I'll get to work on reducing the door height.
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Old 11-24-2009, 05:11 PM
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Location: Vancouver Island
Posts: 1,374
Default Re: Oven height

I agree with Eric. Your door height should be about 13 7/8 " to give the magic ratio of 63%. This allows the fumes from the fire to give up most of their heat to the bricks before cooling and exiting the oven door.

Can you fit a metal insert of some sort at the top ?.

Last edited by Neil2; 11-25-2009 at 06:51 PM.
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  #5  
Old 11-24-2009, 05:23 PM
Serf
 
Join Date: Nov 2009
Location: Australia, Melbourne
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Default Re: Oven height

Thanks for the reply Neil2, I think I've worked out a way to suspend and mortar in more firebricks, I'll send a pic when its done.

Many thanks!
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  #6  
Old 11-24-2009, 10:10 PM
Jed Jed is offline
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Location: Bend, Oregon; West Coast USA
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Default Re: Oven height

Hey Enzo,

Send along a bit more information about how you use your oven. Like, when you build the fire is it a rip - snorting affair with scarry big flames? or are you maintaining a whimpy little fire...

And for how long? do you keep the fire going for a half hour or do you keep it blazing for two hours?

Do you have an infrared thermometer? Do you know what temp's you are getting in the oven? Does your dome 'go white' meaning the fire and the brick is hot enough the black soot and carbon from the fire is burned off the brick in the cooking chamber and the brick look clean.

I have read conflicting information over time, and don't know the magic 63% door height is all that critical,,, ie. folks are getting fine results with different door sizes. So, your door size will definatley let more heat escape than a smaller door hole, but that may not be the major issue.

Is your oven insulated? How much of what insulation under the cooking floor? and how much on the walls and ceiling of the cooking chamber..

And, have you completed a full 'curing' process for your oven. If your oven is new, it takes a good dozen fires, after the oven is 'cured' before you performance will get good. - the first fires continue to drive moisture from the masonry of the oven - and the moisture robs the oven of heat. So until all of the moisture is gone, the oven performance will be 'iffy'.

Just some idea's..

JED

Last edited by Jed; 11-24-2009 at 10:13 PM.
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  #7  
Old 11-25-2009, 12:17 AM
Serf
 
Join Date: Nov 2009
Location: Australia, Melbourne
Posts: 20
Default Re: Oven height

Hi there Jed!
Thanks for the reply. I've fired it off about 4 or 5 times to date, my supplier tells me that real firebrick ovens don't have to cure, "they're good to go straight after construction". I have used several forms of insulation, 20mm of ShiraCast (which is refractory mortar for filling gaps), on top of that I have ShiraLite (refractory mortar for insulation 20mm), then 2 woolen blankets held down by wire netting and about 50mm of general purpose mortar. Under the floor is some sort of fibro sheet about 20mm thick. I've been told you can't over insulate you WFO, but I reckon I gave it good try.

I think your point about wimpy fires is more valid, whilst they haven't exactly been wimpy I think they should be more scarier and for longer.

Thanks for your advise Jed I'll fire up big time on the weekend.
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  #8  
Old 11-25-2009, 12:26 AM
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Location: Australia, Melbourne
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Default Chalky residue on bricks???

Anybody have a clue about this white chalky residue on firebricks.
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  #9  
Old 11-25-2009, 04:43 AM
Il Pizzaiolo
 
Join Date: Mar 2009
Location: USA
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Default Re: Oven height

Avoiding Efflorescence | Storyhey enzo,,, try the second link(at bottom of page) as well it seems to have some better info

Not sure if this is the same,,, but sounds like it...

we poured a band of integrally colored black concrete. It looked great for three days, but then it rained a little the night of the third day, and by the next morning all the black color had disappeared, hidden by a grayish-white surface discoloration. What happened, and how do I fix this?

Answer:
This is one of the most common but least understood phenomenons with concrete. Efflorescence is a chalky white salt residue that can occur with any product containing cement. As moisture migrates up to the surface of the concrete, it carries along with it calcium salts from within the concrete. When the salts reach the surface, they react with CO2 in the air and form insoluble calcium carbonate. This white, dusty, scaly salt can be minimal or dramatic, depending on the amount of free calcium salt present in the concrete. Exposure to rain, standing water, and sprinklers only make the situation worse, as water triggers the reaction and creates more efflorescence.

Efflorescence is not as noticeable when it occurs on gray concrete, but even a little efflorescence on colored concrete can be a contractor’s worst nightmare. Efflorescence makes red look pink, brown look tan, and black look gray or even white. The good news is that it will eventually go away on its own as the free calcium is depleted. The bad news is that this can take as long as 15 years. And in this situation, you can’t wait.

To fix the problem at this point, clean the surface with a mild acid or efflorescence remover (some manufacturers make special efflorescence cleaners) followed by sealing. To avoid the problem altogether on future projects, consider using a colored curing compound or cure and seal to match the color of the concrete. To learn more about efflorescence, read my other blog entries on the topic: Causes of Efflorescence on a Stamped Overlay and Efflorescence Hides Integral Color.

found it at Concrete - Contractors, Info and Ideas - The Concrete Network

Cheers
Mark

Last edited by ThisOldGarageNJ; 11-25-2009 at 04:50 AM.
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  #10  
Old 01-27-2010, 10:28 PM
Peasant
 
Join Date: Jul 2009
Location: Melbourne Australia
Posts: 39
Default Re: Oven height

Quote:
Originally Posted by enzo View Post
Hi there Jed!
Thanks for the reply. I've fired it off about 4 or 5 times to date, my supplier tells me that real firebrick ovens don't have to cure, "they're good to go straight after construction". I have used several forms of insulation, 20mm of ShiraCast (which is refractory mortar for filling gaps), on top of that I have ShiraLite (refractory mortar for insulation 20mm), then 2 woolen blankets held down by wire netting and about 50mm of general purpose mortar. Under the floor is some sort of fibro sheet about 20mm thick. I've been told you can't over insulate you WFO, but I reckon I gave it good try.

I think your point about wimpy fires is more valid, whilst they haven't exactly been wimpy I think they should be more scarier and for longer.

Thanks for your advise Jed I'll fire up big time on the weekend.
Enzo,
Your post struck me because your the only person who has used SHERALITE and im using it also.
I'm also a newbie with WFO however I done a great deal of research before I started to build and I just finished the dome today using fire bricks.
I could be wrong but it appears that your WFO is a arch shape as opposed to a dome is this correct?
I to was going to build a arch shape WFO because it's so much easier then building a dome shaped oven, especially when cutting fire bricks, while doing the research every single site or person I spoke with said that you cannot compare a ARCH shaped WFO to a DOME shaped WFO the basic reason is because a arch WFO has corners as opposed to a dome having no corners.
Apparently with arch WFO the heat cannot circulate evenly and many experts in WFO estimate that a arch WFO will not maintain its heat as well as a dome WFO. They estimate between 20% to 30% in heat loss and maintaining a consistent temperature compared to a dome WFO of similar dimensions.

If I am correct is saying your WFO is of a arch shape with a 22 inch interior height and your door height is 19 inches high then this is defiantly the reason why your WFO is not reaching and maintaining a consistent temperature.
Also regarding your insulation on top of your fire brick did you apply only 20mm of SHIRALITE?
As I mentioned I'm also using SHERALITE and im treating it the same as Vermiculite and most stipulate that you use 4 inches or 100mm on top of your fire bricks, so this could also be a issue why it's not maintaining heat.
I don't think your foundation is much of a issue because you have used some type of insulating board.
My foundation below where my fire bricks sit, the first layer is a 4 inch thick concrete slab and then another 4 inches of Sheralite on top of the concrete and then I put a 20 mm insulation board like yours because it gives a more level surface to lay the floor Fire Bricks, although that's over kill what I did regarding the foundation. I'm more concerned about your WFO door height first and for most and secondly the amount of SHERALITE you used as a insulator over your firebricks.

P.s. I know your post is a few months old now and I noticed you mentioned that you had only fired your WFO 4 times, hopefully by now it's had allot more use and working better. How are you finding it now? I hope its working allot better mate.

Regards
Dean
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