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karl 07-20-2008 12:36 AM

Heat data

In the FB (and other) descriptions/instructions it is often referred to the thermal mass of your oven. This mass is crucial for the heat-up time and the baking time (together with a good insulation to reduce heat loss). Practising your oven will of course give you the best procedures and "rules" for these times and the oven temperature.
For planning purposes the more scientific approach would also be intersting (and possibly helpful?). I know how many bricks (and their mass) my oven dome and floor will consist of and I know (approximately) how much dry mortar I will use. If I knew the specific heats of theses materials (from say 15 C which is the lowest useful for cooking and up to 600 C which is the practical maximum) I would be able to estimate the thermal mass of different design (using more bricks or more mortar). Applying and estimate for heat loss (experience) would also give me an estimate of heat-up and cool-down times. Can someone out there help with the specific heat data?

regards from Karl

karl 07-21-2008 09:23 AM

Re: Heat data
Not much response to this one! Obviously not in the centre of peoples mind. I have managed to find a value for heat capacity of fire bricks : 1,05 kJ/kg K. No similar luck for dried mortar, but I am sure I can use the same value without to much error.

rlf5 07-21-2008 10:42 AM

Re: Heat data
What kind of mortar are you using? Depending on its composition, you can have a pretty good difference in heat capacity values. Although, if you plan to have minimal mortar joints, it may turn out to be negligible compared to the bricks. Good luck!

Carl 07-21-2008 12:25 PM

Re: Heat data

If it's any help, there's a load of data from my oven here:

Wlodek's clever with physics, and he was able to do a lot of mathematical stuff with my numbers to tell me the efficiency of my oven's insulation. If anyone could help you, he probably could.


karl 07-21-2008 01:13 PM

Re: Heat data
Thank's Carl,

I read through the complete discussion in your reference. It did answer a lot of my questions which also were the basis for another issue I have raised in the Forum, - using Siporex blocks for heath insulation. Siporex is the trade name for AAC blocks in Norway. So now I am very comfortable in continuing with my oven on that basis. Unless of course you have had any negative experiences with your oven (AAC experience that is) from last year?

regards from Karl

Carl 07-21-2008 01:48 PM

Re: Heat data
Glad to help. I've had no problem with the AAC yet, but did notice that they get fragile after heating (see my post about my door failure). My oven still seems solid though after a dozen firings or so, but time will tell. If I was building a more expensive oven I'd be tempted to try a layer of insulating board or vermicucrete over the AAC just in case, to protect them from the worst of the heat. They're obviously not a refractory material, but seem to be going strong at the moment.

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