Heat retention

[klaatu]

Hello to all,

My name is Rick Keenan and I live in Charlotte NC , USA. I'm a boss and a dirty fingernail.
I build stuff for a living. All kinds of stuff. I've built a radio controlled J-3 Cub and I've done
the full sized Cub too. Buildings , boats, cars, houses , I really don't care as long as we can
agree on a price. Back in The Corp we broke things, all kinds of things. Now I prefer to put
things together.

Two of our friends have WFO's . One is a pre cast type and the other is layed up brick.
Both are round. Both were at the homes when purchased. The food that comes out of
the both of them is great.

The pre cast one takes 75min to 90min to burn clear with an additional 30min burn to
soak in the heat. After the pizzas, the fire is cleared out and some food goes in ( a chicken,
some potatoes ,some garlic, a cobbler) . 120min later and the little bi metal temp guage
says 250F. If you burn for 4hrs it will be the same. My guess is that it is thin walled
and or badly insulated.

The brick one needs 4or5 hours get right but man o man it sure stays right. He can
cycle stuff in and out for 8 hours and in the morning it usually is 250F or more. I'm guessing
a firebrick , 8" of cladding and well insulated.

I'm looking for the "Goldilocs" setup. As Rod use to say, " Imagine if you will." I fire up the oven and get it burn white. Push the fire over and swabb the deck. 3-4 pizzas later, push the fire back to the middle, add 3or4 more 1" peices of soft wood close the outer door and open the door vents. 20 min later,sweep it out and close inner door. 1/2hr later add steam and 6 -2lb loaves,45mins later 2 drunken chickens, a 4lb meatloaf , 6 heads of garlic ,bake a half dozen taters. 1 1/2hrs later.Then a cobbler or something. Then dry out the next batch of wood. This is on a 2 to2 1/2hr burn.

If I could get that out of a round oven twice a/wk I'd be happy. Would a home built oven with a
42" dia. X 21" dome and a 13 1/4"tall X16"wide inner door with one firebrick, 1"of cladding and perlite bring me this? Would 2" of cladding , how about 3"? The hearth is one brick in a herringbone
pattern run out to the outer door. 3" of perlcrete under it and perlite over it.

I've seen guys write in on differant sites saying that thier dome turned white after a 45min
burn , did 12 16" pizzas, 8 2lb loaves of bread,2 pies, 2 chickens, a goose ,a 4"X12"X12" lasgna
6heads of garlic, the partridge and dried out the pear tree for the next burn. The next morning
still at 350F.

Okay, I once caught a fish thiiiiiiiiiiiiiiiiiiiiiiissssssss big. I'd like a less than 2 1/2hr burn and not
drop under 300F for atleast 5hrs. So , how much cladding above and perlcrete under ? I'm just
trying to get in the ballpark.
Rick,
<klaatu22@hotmail.com>
A long haired, over-fed, leaping gnome.

[DrakeRemoray]

Re: Heat retention

Great post!

I have a 38" Dia x 21" dome with a 19" Wide x 12" tall opening.

I have about 1 inch of cladding outside of the bricks and tons of insulation (about 2" of blanket and 3-4" or more of perlite).

The dome starts to get white at about 50 minutes and goes fully white in 1 hour. If I cook pizza for an hour and keep the heat going, it will be at 550 for two hours or more after I remove the fire. It will still be at 350 12 hours later. Really! I am still learning, but at this point most of my trouble for baking has been that the oven is too hot for too long. I had a bake once where the oven temp dropped too quickly, but I had not cooked pizza, just fired it for baking and removed the fire as soon as the dome was white. I think it needs to charge beyond that a little.

So If you can feel hot flames of fire roaring at your back, I say, spill the wine and take that pearl!

Drake

[maver]

Re: Heat retention

The pre cast one takes 75min to 90min to burn clear with an additional 30min burn to soak in the heat. After the pizzas, the fire is cleared out and some food goes in ( a chicken, some potatoes ,some garlic, a cobbler) . 120min later and the little bi metal temp guage says 250F. If you burn for 4hrs it will be the same. My guess is that it is thin walled and or badly insulated.

I agree, this sounds like it is poorly insulated.

The brick one needs 4or5 hours get right but man o man it sure stays right. He can cycle stuff in and out for 8 hours and in the morning it usually is 250F or more. I'm guessing a firebrick , 8" of cladding and well insulated..

I think you are also right here, the cladding is likely very thick, but it may also have inadequate insulation. Other variables include how well seasoned the wood used is and how 'aggressive' the fire is. Robert Musa has been quoted here as saying something to the effect of 'you want a fire that makes the kids say "yeah, dad, add more wood" and your wife say "if you add another piece of wood I'm calling the fire department".' Do you know what temperature either of your friend's oven reaches? I will make pizza in an oven anywhere from 700 (a bit too cool, usually only if in a hurry or I get distracted in my oven temperature management) to 850 (I've used 900 hard to avoid some portion of your pizza burnt beyond good eating).

Would a home built oven with a 42" dia. X 21" dome and a 13 1/4"tall X16"wide inner door with one firebrick, 1"of cladding and perlite bring me this? Would 2" of cladding , how about 3"? The hearth is one brick in a herringbone pattern run out to the outer door. 3" of perlcrete under it and perlite over it..

With a dome made of 1/2 firebricks (4.5") 1" of cladding should be more than sufficient if you have good insulation. 3" perlcrete under should be adequate, and you want 6" at least over the dome (or better yet, a ceramic fiber insulating blanket and less perlite). I am interested in some of the recent forum posts here regarding a thinner dome with no cladding (3"). I suspect that would heat up faster, I'm just not sure how long heat would be retained. If your primary purpose is pizza then this may be superior. Since you are interested in varied uses, I'd use 1" cladding (I have just a little less than that) with 4.5" bricks.

I've seen guys write in on differant sites saying that thier dome turned white after a 45min burn , did 12 16" pizzas, 8 2lb loaves of bread,2 pies, 2 chickens, a goose ,a 4"X12"X12" lasgna 6heads of garlic, the partridge and dried out the pear tree for the next burn. The next morning
still at 350F..

You'll find similar posts here. Realistically, if I have my oven in fairly frequent use (so that the bricks haven't taken on moisture) I have a 60" burn time (with white dome) before pizza is ready to go. If I were to do 12 pizzas, by the time the oven has been kept hot for that long (another hour or so - less when I start using my outdoor prep area) then it takes an hour to drop the oven to baguette temperature (around 600). After that I can roast meat or cook some beans. If I do use the oven to dry wood for the next use the oven will probably be cool the next morning (I have not checked temps with this). If I just put the door on with a pot of beans in the oven, it's still usually 320-330 the next morning.

Okay, I once caught a fish thiiiiiiiiiiiiiiiiiiiiiiissssssss big. I'd like a less than 2 1/2hr burn and not drop under 300F for atleast 5hrs. So , how much cladding above and perlcrete under ? I'm just trying to get in the ballpark.
Rick,

I think the 2 ovens you are experienced with are not performing ideally - many have posted here with experiences of faster than 2 1/2 hour burns and high temps the next morning (I guess it depends how long you sleep in though). As a counter example, my father built an oven with little insulation and the flu in the dome rather than in front of the door area. His oven takes 3 hours with an aggressive fire to bring to heat, and still only reached 3-4 minute pizza temps rather than about 2" with my better insulated oven. Keep to 1" cladding maximum and insulate well - you'll see.

Marc

[james]

Re: Heat retention

Hey Maver,

Robert's wife definitely did not say "if you add another piece of wood I'm calling the fire department" -- it was much better than that.

Great postings all. Excellent. My only contribution is that if you insulate the heck out your oven, you will be amazed at how much heat a 2"-3" oven will hold. Pizzerias with 3" thick ovens bake bread for the restaurant using retained heat every morning. Bigger isn't always better.
James