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jeff 03-16-2008 07:03 AM

Cooling curves
Hey, just for a giggle: who's got cooling curves/stats for their oven?
After 24hr, we seem to drop by 1.5*C/hr. Seem reasonable, or should I chuck on more blankets?
And nonono, this ain't meant to be scientific; anecdotes are far more useful, eh.
I'd just love someone to hijack this post, and set some criteria so we could standardise the data.(Mind you, those of us with low-energy memory cells may well skew the figures, eh.) Hahaha, gotter love it.
Go the Boffins.

Frances 03-16-2008 09:15 AM

Re: Cooling curves
Gosh Jeff, you really have lost your luddite leanings, haven't you?

I could certainly write down my cooling curve - sorry, my oven's cooling curve, but the best you're going to get is a snap shot of a crummy piece of paper with a lot of scribbly notes on it... and you seem to be talking computer graphics here :eek: :eek:

carioca 03-16-2008 11:06 PM

Re: Cooling curves
Let me throw you a quick curve, Jeff: I backed two sourdough loaves (my first attempt) yesterday afternoon when the oven temperature was at around 220C - this morning when I checked the temperature (with insulating door in place overnight) was down by 100C to about 120C.

Do I need to improve the insulation? (Which would mean tear down two coats of cement render, wire mesh, vermiculate cement mix and put another layer of blanket, i.e. end up with 7.5 cm of blanket, then redo vermicrete and render? Not to mention the paint job :-)

Or is it just a question of loading up the oven more thoroughly with heat? I tend to cut corners here because at 28C ambient temperature, it's bloody hard work for this old gnome to split and chop hardwood billets...



talisker63 03-17-2008 01:01 AM

Re: Cooling curves
Carioca, excellent question.

To add more insulation MUST it go underneath the render or can you just add more blankets and then re-render on top?

I can see why it would matter where the insulation was, it's still retaining heat..?

Frances 03-17-2008 04:02 AM

Re: Cooling curves
I would have thought it would be far better to insulate below the render, if at all possible. Just a feeling though.

And I just realised, I have a constructive contribution to this thread after all :):

My oven cools down far faster to begin with, say down from pizza temps to bread baking temps (240 - 200 C) in two or three hours. But then it seems to hover around 100 to 80 C for like two whole days. Do other ovens do this, too?

I thought it might be because the difference between inside and outside temperatures is so much bigger to begin with so more heat gets lost faster, and vice versa. But thats just guessing...

jeff 03-17-2008 06:10 AM

Re: Cooling curves
Amazing how a single word can impact upon the concept of cooling curves, eh.
Luddite leanings are very much alive and kicking Matess. Second only to my social ineptitude is my ignorance re modern flash-murry, space-age technology.This WFO stuff is a refreshing walk-in-the-park for me, as is chatting with people with not dissimilar interests.
@!@#$%^&*()_+|Buggerit!! Slam. (Not good).
Flamin luddite to the core.(BTW. I can't even fix me own bloody car these days!!)
OK. Finish that. Let's go the Trivia.
As always Frances, you're on top.
Initial losses are extreme. 1 degree C per minute in my case, grading down to roughly 1.5 C/hr of that @ 50 hr.
Apologies to those I misled, eh.

Carioca, where is Charlotte Bay? Facing the Great Southern Ocean would be my guess.Somewhere near the SA/Vic border? We have Princess Charlotte Bay just up the way a bit, but then I'm a cane-toad, tru.(QUEENSland, eh.)
LMH, I'd guess at firing times. Just cut yer logs into lengths you can hump, an feedem in bit by bit. Stuff splitting 'em, eh, unless you grow larger trees than I remember . (Oh Oh. Not from 'round Denmark, are you?)
11pm temp check showed 71C in the atrium, 171 in the oven. So that's around 300* drop in 30 hr, or 10/hr. Seems that the first 3hr saw a 180 degree loss, so the trick is to cash-in on residual heat.
Fellers, this is just a chuck-in-the-air-an see what happens.
Thanks eh.

pjk 03-18-2008 06:20 AM

Re: Cooling curves

Interesting topic, and it relates somewhat to one that I raised a few months ago, and which never really got answered. I don't have the answers, but will throw my quandry into the mix.

We have a lot of discussion on the site in relation to the benefit of good insulation, the value of which is undeniable in terms of heat loss.

What I can't find a lot of info or answers on, is the relationship of the insulating properties/value relative to the amount of heat mass that is used in the oven.

To my mind, you can insulate until the cows come home, but unless you are protecting enough heat generated by the relative heat mass, then you might not be insulating anything but the insulation.

Is there any information, or can anyone explain the relationship in proportionate terms between the heat mass in an oven and the amount of insulation.

I'm struggling a little with comparing two different ovens in terms of heat retention purely on the basis of insulation, for instance, with one oven having 4 inches of insulation and the other 8 inches, if both have differing characteristics in terms of heat mass.

Or, are we assuming that the heat mass is always a standard one brick wide (110mm/4 1/2 inch wide give or take) ?

After a few months rooting around with structural stuff I'm about ready to build the oven/s, and I'd love to understand the mass/insulation relationship thing better becuase I think it holds the key to getting, and then holding the tempratures you may want to generate in your particular oven given its' intended use. I figure that I'll probabaly only get build this once, so would like to get as close to right as possible. Then again I've stuffed up some of the structural stuff a little, plus I built the "one hour temp oven" that gets by ok, so maybe it it will all be fine regardless.


jeff 03-18-2008 07:44 AM

Re: Cooling curves
Living a bit N of Melbourne?
Don't know the country, but looks good on a drive-through. Stuff your climate though mate.
Peter, I'm least qualified to comment, but stuffit. Lookout.May others destroy my technique. (I'll just go and sook eh. Hahaha)
I rejuvinated an old Aussie barbecue. Tore it down to old base (about 6 courses high), and layed a round front up to that level.Had big mobs of custom orb and reflective foil insulation on hand, so that, plus vermiculite, formed the sub base. 75mm vermicrete on top of that completed sub-floor insulation.
Next a layer of paving tiles 50 thick, with an identical layer on top, but cut to fit within the dome.
Dome is made of solid common creams, halved, with a 50 layer of vermicrete over that.Next is almost 50 of ceramic blanket. (Not enough for 2 full layers, eh.)
The next bit is divergent, (as was the base). Formed 'packets' using reflective foil insulation, placed them over the dome, then filled'em with vermiculite.Bird wire and barbed wire frame over that lot (Use what's to hand, eh. Mad if you don't). Flicked a rich sand/lime/cement through that to stiffen the foil, then rendered with maybe 20 sand/etc.
Peter, while the system seems OK, I don't know how time will screw the reflective qualities of the foil: badly, I suspect.
I have the luxury of building this oven as an experiment; not much I'll change next time I reckon.
But in answer to your question, half bricks (plus a bonding coat, eh), seems to justify a nice mink coat.
She'll be right mate.

carioca 03-18-2008 06:55 PM

Re: Cooling curves

Originally Posted by talisker63 (Post 26740)
Carioca, excellent question.

To add more insulation MUST it go underneath the render or can you just add more blankets and then re-render on top?

I can see why it would matter where the insulation was, it's still retaining heat..?

A valid question in answer to my question :-)

I tend to agree with your view that one COULD of course ADD more blankets on top of the dome, then re-mesh and re-render and re-paint -- the physical outcome ought to be the same IMHO: MORE heat retention due to more insulation...



carioca 03-18-2008 07:11 PM

Re: Cooling curves

Originally Posted by jeff (Post 26753)

Carioca, where is Charlotte Bay? Facing the Great Southern Ocean would be my guess.Somewhere near the SA/Vic border? We have Princess Charlotte Bay just up the way a bit, but then I'm a cane-toad, tru.(QUEENSland, eh.)

LMH, I'd guess at firing times. <SNIP>


Hi Jeff,

I'll answer for both carioca and LMH, seeing I answer to both IDs...

If I pointed you to the map on my picasaweb album (pls see my profile), you'd see the Google Earth view of my whereabouts: some 30 km south of Forster (pronounced Foster by the locals), within earshot of the Pacific (1.5 km from the beaches at Pacific Palms, a.k.a. 'North Mosman' by those refugees from Balmoral, Sydney, as your truly :-)

The same album also contains shots of the size of some of the big fellas I toppled, most recently a lovely eucalypt that was treading too close to the oven site. And it's this one I've been splitting lately for firewood, seeing that it's had a year's worth of drying time...

Re the temps: I was indeed rather shocked by the rapid initial cooling rate (down 100C overnight from the baking temp, but the oven seems to hold up well on subsequent days, thus bearing out Frances' contention. I IR-ed 48 hours after the bread baking, and it still showed about 70C all round on my AJH 8895 laser-guided temperature probe, which I bought for around $A145 from the distributor... (As always, I manage to pay premium for anything I buy, that goes for the $A3500 Monitherm monochrome hi-res screen I acquired back in 1989 and so on :-)

Best of luck among the cane toads, mate!


Carioca a.k.a. LMH

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