High Heat Loss

[ThisOldGarageNJ]

Re: High Heat Loss

Like Dutch said, can you get the floor out of the oven ? Using half bricks and insulation board ight be your best way to go... Then call the guy who built it and tell him he owes you a refund !!!

Hope it works out for you
Mark

[dmun]

Re: High Heat Loss

I had an idea that might work but I`ll ask here first.. I was thinking along the lines of insulated cement tiles about an inch thick..I would have to make them in a small form sandwiching the the insulating board on all sides inside the cement.. No idea yet if they would crack or not but thought that if it works then I would have an oven that I could use for bread or Pizza`s by simply placing or removing the tiles..
Do you think this could work?
I live in the Philippines so might have some problems finding the insulating board..
What If I just made them from a perlite cement mix?

An inch of perlite concrete is better than nothing, but not much better. Four inches is the recommended amount. Reducing that still further by putting concrete on top (You can get refractory concrete, but not insulation board?) sounds like a big waste of time to me.

[ThisOldGarageNJ]

Re: High Heat Loss

hey guys,
What if he were to stucco the inside of the oven with refractory cement, if he put kaowool inside, then wire mesh and stuccoed with the refractory ????

Any thoughts on that ??
Cheers
Mark

[Archena]

Re: High Heat Loss

Um, wouldn't that insulate the bricks from the heat? It's the thermal mass that holds the heat and radiates it back into the oven. Insulation is supposed to keep heat in - but if the bricks can't absorb it, wouldn't the oven cool faster?

[ThisOldGarageNJ]

Re: High Heat Loss

arch,,
what i am trying to do here is put a band aid on a gaping wound.... My thoughts it would work better this way than the way it is....You put vermicrete over your insulation to keep and hold heat right ... this is kind of the same thing not as good but better than it was.. Just a thought...
Cheers
Mark

[Archena]

Re: High Heat Loss

Yeah, I realize that but I'm wondering if reducing the working thermal mass wouldn't create the exact same problem as the excessive, uninsulated mass - the inability to hold heat correctly?

I dunno - just asking. I'm strictly peanut gallery here.

[ThisOldGarageNJ]

Re: High Heat Loss

arch,, I dont think I can explain what im saying in my words,, But,, Lets say that, thats what I would do If I had the same problem... I think it would keep the heat from being wicked away by the excessive amount of plain concrete in the dome.. Hoping the bricks would Insulate the Isowool and refractory cement.... I think

[Archena]

Re: High Heat Loss

<eats peanuts>

[fred42]

Re: High Heat Loss

Since my last suggestion of perlte tiles I have discovered that my oven gets consistently hot enough to cook large pizzas in just under a minute..The floor and brick arch turn white.. Takes about 3 hours before I can feel the heat coming from the bottom of the 5 inch slab and Ive still to insulate the dome with any thing at all.. When my perlite arrives to insulate my barrell dome i was thinking of going into the nickel smelting business..
What do you reckon??

Fred.

[Archena]

Re: High Heat Loss

Try tin instead - you could make pewter!








Congrats!

[crowtrapper]

Re: High Heat Loss

FWIW, I really think demolition and a rebuild would be the best option. I have been using my oven now for about 9 months and everything is fine except that heat retention is a bit weak.

Basically I used the FB design for a home built dome but the only thing I skimped on was the floor - instead of a concrete supporting base, then a layer of vermiculite concrete, then a firebrick hearth, which all seemed to be a bit time consuming (ha!) I used AAC panels as a support for the firebrick hearth. Kills 2 birds with one stone, yes? support and insulation? Well, no, not really. The oven works OK but heat loss is far too rapid for my liking, mostly through the floor rather than the dome. The dome is standard FB style and never even gets warm on the outside.

If I fire it up to pizza heat, then rake the fire out, the temperature seems to drop from 350 C down to about 100 C in only an hour or so. Makes long slow cooking a bit problematic. It is OK but only just. Seriously, if this problem was any more severe I would demolish it and start again.

Already I am planning my NEXT oven!

[Mitchamus]

Re: High Heat Loss

I think the problem seems to be to too short a burn time.

You guys are forgetting that the concrete should work as heat storage.
With that amount of thermal mass, once hot, the oven should stay hot for days! or at least 12 hours....

You should try a burn of 6+ hours. In fact, keep a fire ticking over ALL DAY.
and try again.

You could still be driving out moisture from that amount of mass, which will tend to sap heat from the oven.

Or...

The fire bricks used were insulating rather than refractory bricks.
Which is a knock-down & rebuild situation, but at least you wont have to build the stand!


A good way to test would be to take a temperature reading every 30mins after removing the fire. That's the only way to really see how the thermal mass of your oven is performing.


Don't forget that logically thermal mass and insulation do the same thing,
keep the oven hotter for longer.

Thermal mass stores the heat and radiates it back into the oven - keeping the oven hot.

Insulation stops the heat from escaping - keeping the oven hot.

A well insulated, and well thermal massed oven should perform with similar results as far as heat retention in the oven goes.

The only trade off between the two methods (in terms of heat retention) are fuel efficiency!

(and obviously in turn - heat up time)

[crowtrapper]

Re: High Heat Loss

Yes, must do a continual measurement to see just how fast the heat goes. Firing time could be a bit of an issue - mostly I fire it up and allow about 3 hours which seems to be plenty; have tried a bigger fire for an hour and a half and no, that was NOT long enough. The surfaces were hot but the heat had not diffused sufficiently into the rest of the structure. So - maybe even 3 hours is not enough either.

One of the best results with our oven was an occasion when I was away and our 25 year old son had a fire in there big enough to smelt steel; he rang me in a panic because he thought he might have broken something; and it was hours before the fire died down enough to get near the oven to cook a pizza. It worked perfectly! and nothing broke! Maybe I should learn from that.

[cjt]

Re: High Heat Loss

I have a similar problem although not quite as bad as yours. I can get the temp up and cook quite a few pizzas. My oven floor is firebrick sat on top of 2" of castable insulation under that is a 4" conrete slab with re bar i am finding that when the oven is hot the underside of the slab gets up to 80 C I have been advised to keep on cooking to get rid of moisture but it doesnt seem to be getting any better. is there any harm in me lining under the slab with a sheet of kingspan to keep the heat in ? that way i would be creating a heat store I know it takes longer to heat but once there if held ??? Any advice any one on this similar problem

[happy]

Re: High Heat Loss

i also have high heat loss in the floor and im just finishing up....how devistating....(first build) anyways had a local pizza oven guy just stop by and offer some advice. He suggests building forms from 2x6 and making a vermiculite slab in 4 sections. letting them cure for a week sliding them in the wood storage area and sticking them up with firerock mortor. hows that sound.. i guess it couldn't hurt.............