#11  
Old 07-26-2007, 12:06 PM
CanuckJim's Avatar
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Default Re: High Heat Loss

JCampo,

The best you can do is the best you can do. I'd really follow JE's advice and use high heat glue to install four inches of rigid calcium silicate high heat insulation board under the oven. There will still be radiation into the walls, but there's little you can do about that now. At least you will greatly reduce the heat loss you're experiencing now. Can't believe your builders did it the way they did. Not good, won't work.

I should know on Monday about a local source for the board and blanket insulation. High temp glue can be found at fireplace/woodstove suppliers.

As for the loose insulation for the enclosure, you can get large bags of vermiculite from pool installers or suppliers. It's called PoolPac. I got mine from Bathe & McClellan in Whitby. If you can actually climb inside the enclosure, the very best thing would be to wrap the dome in high heat blanket insulation, then pour in the vermiculite.

I don't think another layer of firebrick will have much of an effect, and it might adversely affect draught.

It's a fair bit of work, and some expense, but it will be worth it. Whoever built your oven should go into another line of work.

Jim
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  #12  
Old 07-26-2007, 12:32 PM
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Default Re: High Heat Loss

If you have a structure similar to the photo your battle is half way won.
As Patrick (jengineer) has noted; you need to access the area above/around the dome (under the roof of the 'house').
Horticultural grade perlite or if more readily available, vermiculite. Try your local garden centers, you will probably need several 6 cubic ft. bags. Fill the area with at least 4", better yet - FILL IT UP!!! Depending on how much access you give yourself will determine whether you would need to 'blow it in' or merely dump in the bags....DRY, no need to mix with cement in an enclosed dome. Remember only use the horticultural grade products...it may also be available in different grades or courseness...the courser the better-don't use the fine grade unless you have too.

As for the hearth insulation. ideally you would want the insulating layer directly under the firebrick and on top of the support slab.....obviously that is not possible at this point. Again, as mentioned, adding one of the insulation board products such as SuperIsol (sold by Forno Bravo) or Cal sil to the underside of the support slab is your best option; accessing through your wood storage area.....the thicker, the better.
This won't be ideal, you will still be heating the entire hearth slab at every firing, but you should see a huge improvement over what you currently have.

Any chance of your posting a few photos, so we can be sure of our recommendations??

RT
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  #13  
Old 07-26-2007, 01:09 PM
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Default Re: High Heat Loss

Thanks for all your help! I will post some pics on Monday so you can see what I have bean venting about.

If you can post any local sources for finding the materials that would be great as well!
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  #14  
Old 07-26-2007, 03:19 PM
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Default Re: High Heat Loss

Quote:
Originally Posted by jcampo View Post
Can i bond an insulation board from underneath that? Is that close enough to the slab to make a difference?
Although you still have a big heat sink in the slab and what it sits on, insulating underneath can't hurt, and it might help. That far away from the fire, you probably don't need refractory insulation - a couple of inches of the pink foam stuff from HD might make a difference. A warning-if it's too hot to hold your hand against when the oven is running it's probably too hot for the pink foam.

The original pompeii ovens had the perlite insulation under the support slab. If your support slab isn't bonded to the block base, you may be able to lift it with post jacks in the corners, and add four inches of perlite concrete after the fact. Might be easier that tearing it down.

Too bad you got here when you did - the oven builders motto is insulate! insulate! insulate!

Last edited by dmun; 07-26-2007 at 03:22 PM.
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  #15  
Old 08-01-2007, 07:39 AM
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Default Re: High Heat Loss

Hi Guys,

Finaly got around to posting some pics of the oven. Did some additional research and I have access underneath the oven via the wood storage area. However above the dome is pretty much filled in with concrete there is no room to add any perlite. I guess my only option is to mount some insulation to the bottom anh hope that helps? As for the the heat loss from the dome am I stuck?
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  #16  
Old 08-01-2007, 07:53 AM
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Default Re: High Heat Loss

JC,

I'd definitely go ahead and insulate the bottom of the oven as best you can. If the area above the dome is really full of concrete, it looks like you are stuck with the heat loss without some very serious retrofitting to the facade of the oven. In effect, it looks like you'd have to build another wall of brick around it and fill the gap between the two walls with insulation. I do hope other members will have a better suggestion for you.

Jim
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  #17  
Old 08-01-2007, 08:21 AM
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Default Re: High Heat Loss

Really full of concrete on top of the dome? You probably have an excellent bread oven...

You should try to do a burn that lasts like 3-4 hours and see if you can get up to pizza temp, or maybe you can retain bread baking temps for multiple bakes...
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  #18  
Old 08-01-2007, 08:39 AM
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Default Re: High Heat Loss

Yup ,full of concrete. I have tried a burn that long (even with a 2-3 hour burn) I can get pizza oven temperatures. As soon as the fire is reduced or stopped the temperature very quickly drops. I can manage to get 1 pizza done the second is not guaranteed.
John
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  #19  
Old 08-01-2007, 09:22 AM
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Default Re: High Heat Loss

John, are you keeping a fire going when your doing pizza? Not a raging fire, just a couple of logs with all of the coals? It makes a huge difference even in a well insulated oven.

RT
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  #20  
Old 08-01-2007, 09:35 AM
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Default Re: High Heat Loss

I know this does not help solve your problem, but have you used an IR thermometer (or any type) to get actual temps and gauge the heat drop off??
Maybe enough heat to do a couple of bread bakes? couple of hours roasting?

I'm just trying to think "worst case scenario" and find a way to use what you have.....its a beautiful oven, there has to be some form of cooking you can do without having to burn an entire forest each time.......I hope so, anyway
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