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taiwanpizzaman 05-03-2007 11:25 PM

pizza oven heat retention
 
Hi guys, great site!:p

I finished my pizza oven about a month ago. The inner dimensions are 85cm x 65cm. The dome height is 45cm. I built the oven based on info I gathered on the internet. I used firebricks for the base, but used normal redbricks for the dome. The reason was financial, the firebricks here in Taiwan are thirty times more expensive than housebricks, no kidding!:( The oven works really well, but it needs an enormous amount of wood to keep it going for pizzas and it doesn't retain heat for baking bread.

A friend of mine here builds kilns and he suggested raising the oven floor with another layer of firebricks to reduce the dome height. The oven chimney is in front so it looks like the cool air sucked in at the bottom is cooling the oven too much. I was thinking about using fireclay and mortar to build another inner dome (with difficulty), to increase the oven's heat retention. Any suggestions will be appreciated.

Colin

dmun 05-04-2007 06:58 AM

Re: pizza oven heat retention
 
I suspect an insulation problem, rather than a masonry mass deficiency. Tell us how your oven is insulated

taiwanpizzaman 05-04-2007 08:05 AM

Re: pizza oven heat retention
 
The oven is insulated with a 12cm coating of baked stone (similar to vermiculite), portland cement and lime. On top of that i have another 10cm of concrete cladding. The initial firing was done with gas and after 26 hours of continuous firing the top of the oven was barely warm. No matter how much I fire it, the top never gets hot and has never cracked, that's why I think it must be the single layer red brick.

Xabia Jim 05-04-2007 01:33 PM

Re: pizza oven heat retention
 
You could try your friend's suggestion using a temporary set of firebricks on the hearth....might be worth the try. If that helps, you could make it permanent.

It's a bit of a puzzle though....why would the red bricks not hold the heat? ....using a lot of wood should build up the thermal mass in the masonry.

It can't hurt to put an additonal layer of insulation around your oven. What about a door and chimney cover to keep the heat in longer for bread?

Maybe post a few pictures....

Good luck....Jim

maver 05-04-2007 01:51 PM

Re: pizza oven heat retention
 
before you add insulation or another layer of firebricks (which would increase the mass of the floor - possibly aggravating the problem) try a draft door to verify whether your concern about drawing too much cold air is an issue. By your dimensions I presume this is a barrel oven as well. Could you be more specific about the insulation under the hearth and what the order of layers in your dome is? If you do add a firebrick layer to the hearth you should also include a layer of insulating board under that. Given the cost of firebrick you might take as much of your existing hearth out, place in a layer of insulating board and then brick back on top. If you have to adjust the height further then use ordinary red birck under the insulation. My 2 cents.

taiwanpizzaman 05-04-2007 03:31 PM

Re: pizza oven heat retention
 
1 Attachment(s)
Hi guys

Thanks for your input. I've used a door with a thermometer in it. The initial temperature with only the bed of coals and ashes goes up to 160 degrees celcius and then quiclkly drops to 140 degrees in about twenty minutes. Over the next two hours it drops to about a 100 degrees which it holds for five hours. After about twelve hours the temperature is between seventy and eighty degrees.

The hearth base consists of 10cm concrete, 10cm building sand and then black firebricks. These firebricks are used for the temple furnaces and are rated to 1000 degrees celcius. They hold the heat extremely well, they remain warm eighteen hours after firing. I've included some pics.

RTflorida 05-04-2007 04:46 PM

Re: pizza oven heat retention
 
I'm not too familiar with the barrel vault concept, but, based on the picture - could the entry be too large??? Looks quite large in relation to your internal measurements. This could be the source of drawing too much cool air. I would also think you would need a well sealing, insulated door to have a chance at retaining much heat.

RT

spareRib 05-04-2007 06:04 PM

Re: pizza oven heat retention
 
Indeed, it looks like the door is the same height/width as the cooking chamber and quite shallow compared to the size of the opening? You might want to compare with the dimensions of Alan Scott's designs.

taiwanpizzaman 05-04-2007 07:53 PM

Re: pizza oven heat retention
 
Hi guys

The picture was only to show how the barrel was formed during building and the insulating material on top. After that the front section, chimney and door was built at 63% of the dome height. More insulating material was added to the front and then the entire dome was covered with 10cm concrete. I used that picture because I want to know if that single layer of brick is enough to retain the heat in the pizza oven.

Thanks
Colin

spareRib 05-04-2007 08:37 PM

Re: pizza oven heat retention
 
Everything I've read suggests that a single layer of red brick should be sufficient. Likewise, with 10cm of concrete/vermiculite, you shouldn't have a mass problem and black bricks should absorb a fair bit of heat. How big of a fire are you building, what materials are you burning and how long does it take to burn down?


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