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windows in my oven

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km.portree's picture
km.portree

windows in my oven

windows in my oven

 

I am soon to begin building a wood fired oven and would like to float some ideas for comment by forum members. 1.My design includes two windows, one either side of the opening to the oven. I anticipate they will be triple glazed with the inner pane of fire glass. They would be attached (heat mastic I guess) to an angle iron frame which extends the whole way across the front of the oven. 2. Because of this frame I would make an extension out from the oven to pick up the flue (may need "posts in front as well to carry the weight of the flue. Does anyone think the upward draft of the flue would be adversely affected by having the flue open on three sides? My reason for doing it this way is to unclutter the oven opening for putting loaves in out. 3. I intend to use fire board and fibre blanket for insulation (50mm on top and 50mm underneath) and my hearth bricks as well as arch bricks laid on their side (115mm). Under the bricks (and on arch) I was thinking to put 50 or 75mm of concrete. Ie 115+50 =165 mm before insulation. Is this enough thermal mass or too much? Useage will be typically 10-12 pizzas followed by 5-6 loaves of bread per firing. I'd be grateful for any comments from those with more experience. km.portree

ClimbHi's picture
ClimbHi

Why?

First, windows seem like a lot of complication with questionable outcome for little gain. I doubt attaching glass with mastic in a 1,200° environment would work. Further, even triple pane glass will introduce some serious heat loss. Don't believe it? Just put your hand on your kitchen oven window when the oven is set for max and imagine what it would feel like if your kitchen oven could get 3X as hot. Or stand in front of a fireplace with glass doors and feel all the heat radiating away that would otherwise be soaked up by oven walls.

Second, what exactly do you want to see through your windows? No need for windows for pizza, since you can see it just fine through the door. Little need for windows for anything else since once you have used your oven for a bit, you don't need to watch the bake constantly. Just a peek or two near the end of the bake and you're done.

Third, having all that glass eliminates an equal area of thermal mass, and thus will likely cause uneven baking since the items near the glass won't get as much radiant heat. I once tried to do a double layer bake in my oven, putting items both on and below a Tuscan grill in the oven. The things on top baked fine. The things below, hardly at all since they were shielded from the radiant heat from the dome. WFOs do not cook the same way kitchen ovens do. Kitchen ovens rely on hot air, WFOs rely on mostly on radiation from the oven walls and dome. Eliminating any of the radiant mass will have drastic effect on the baking properties of the oven.

And yes, the design you describe will affect how the flue works, expecially if there is any wind or draft at all, and especially if your oven is to be outdoors. Not an insurmountable problem, but one that may take some experimentation to solve.

As for the thermal mass being too much or too little, that all depends on what you want to bake. Pizza requires little thermal mass since the fire is burning the whole time you're baking. One load of bread doesn't require much more, since a bake only takes about 30 minutes once the oven has cooled/soaked after the pizza or initial firing. Anything requiring more extended baking benefits from more mass. The drawback to added mass is that it means more fuel use and longer firing times. So it all depends on how you want to use your oven. WFO's present an endless balance of compromises. Once size definately does not fit all. But what you describe would probably work fine for pizza and/or a single batch of bread.

ClimbHi
Pittsburgh, PA

DerekL's picture
DerekL

Even with the inner layer being fire glass - you're still talking a lot of radiant and conducted heat.  My guess is that the middle and outer panes wouldn't survive more than a bake or two.  Plus everything ClimbHi said.

km.portree's picture
km.portree

Thank you Climb Hi and DerekL for your comments.

My new domestic oven has triple glazing and allowing for the temperature diffence of home and WFO's it is comfortable to touch so I don't think the heat loss is my main issue.

But, making (or having made) a properly sealed and gas filled glass unit is.  The point about having less thermal mass is relatively insignificant I think as the proportion of glass in the oven interior is minor. The big point though is loss of radiated heat from the front wall.

Think I'll settle for making the door a little wider much as I enjoy looking into an oven and watching the process/progress.

Regarding the thermal mass details do you think a brick on its side (115mm) plus 50mm (or 75mm) of concrete and then the ceramic fibre board (50mm) sounds about right for my intended use?

km.portree

Australia

ClimbHi's picture
ClimbHi

Enough for sure for pizza. Many kit pizza ovens have wall thicknesses of about 1/3 what you propose since retained heat isn't as important for fire-in baking. Sounds fine for a single load of bread as well, since you'll only need to hold temp for less than an hour. If you have doubts, do a test firing before adding the insulating layer and adjust your plans accordingly. But I doubt you'll have any issues with 165 mm of masonry.

ClimbHi
Pittsburgh, PA

shuboyje's picture
shuboyje

I can't believe this is my first post here.  I thought I had commented on a few things here over the last few years, guess I've just been a lurker.  I do post at Fornobravo and pizzamaking.com a bit.  Now on to the meat of my comment.

I would highly recommend a trip over to fornobravo to download the free plans for the pompei oven.  For your uses it will be a much better fit then what you've preposed.  A massive barrel vault oven takes too long to heat up for only 5-6 loaves of bread and doesn't get to the ultra high pizza temperatures you may find you crave.  A pompei oven will heat up faster and maintain a higher cooking temperature for better pizza all while giving you enough heat for way more bread then you are asking.  

As for your window there is a solution.  Instead of a permanent fixture of the oven that has to survive live fire you can build a glass oven door.  When the fire is in the oven you do not have the door on so you won't need windows, and when you are cooking on retained heat you can use your glass door to retain the view you desire.  This has been done with good results in the past by simply using a pyrex baking dish, but I would bet you could get very good results with the triple pane construction you mentioned. 

polo's picture
polo

I agree with everything said here, except this comment "A massive barrel vault oven doesn't get to the ultra high pizza temperatures you may find you crave."

The barrel vault will indeed achieve the same temperature that a pompeii style oven will. It will just take longer to get there. My oven is just as capable of burning a pizza as any other oven :) (and can also bake a wonderful 2 minute pie)

I do agree with the other comments and think the door idea is a good one.

shuboyje's picture
shuboyje

That is exactly my point.  A two minute pie is worlds away from my goal.  I run my oven at 1000F on the hearth and cook pies in 40-60 seconds like the top places in Naples.  And I can be there in an hour and do it for hours on end.  I've never seen or heard someone claim their massive barrel vault oven can do that.  Thinner barrel vaults without extra mass in the floor of cladding in the top may be able to, but I don't think a scott style oven for example has a chance in the world.  

This is my taste, and the poster may find they like 700F 2 minute pies which are certainly more of what american expect out of a pizza then the traditional ones, but isn't it nice to have the option to go hotter if you want to?

polo's picture
polo

Fire is fire and firebrick is firebrick. I have most certainly had my oven's hearth and vault at 1000 F. +. You are correct though, I really don't care for the pies that cook so fast. You see, I am not as deft at keeping a close eye on such a pie as you are. My, "massive" as you call it, barrel vault is however just as capable as burning a pie as your oven is. 

The pompeii snob thing doesn't impress me. 

shuboyje's picture
shuboyje

Somewhere I'm coming across wrong.  I'm the furthest thing from a Pompeii snob, I actually point out many of the outright lies and false truths they claim on a fairly regular basis over at fornobravo.  When I use the words "massive barrel vault oven" I'm not using it as some sort of an insult, just a description of a type of oven.  More and more people are building barrel vault ovens that deviate from the Scott plans by placing the insulation over the structural hearth and not cladding the dome so I feel the need to describe what I'm talking about.  

There is nothing wrong with a massive barrel vault oven, it just isn't the right oven for this user.  I'd bet you bake a large amount of bread now or at some point did or plan to.  Thats where that oven shines and I'm sure you know that.  It has a ton of thermal mass that is great for holding bread baking temperatures for a long time after a long fire.  I'm simply citing basic thermodynamics when I say this oven will not run as hot as a pompeii or other similar ovens.  A pompeii oven has 4.5 inches of mass in the dome and 2.5 in the floor.  I've seen scott style ovens with 4.5 inches of firebrick in the floor and an additional 6 inches of concrete before the insulation.  Heat transfers from hot to cold, so in Pompeii oven you only have to heat 4.5 inches of mass in the dome a and 2.5 in the floor before the deeper mass stops stealing heat from the surface.  I'd wager to say you will never get the outer surface of  a scott ovens thermal mass up to 1000F, so that outer mass will always be stealing heat away from the surface.  Add to that the fact that many Scott style ovens do not insulate around the structural hearth and therefore create a giant surface area of hot concrete radiating heat away from the ovens deck.

Hopefully this explains where I'm coming from a bit better.  

polo's picture
polo

In my first response to your first post in this thread I agreed with all of your comments regarding the differences between Pompeii and barrel vault ovens, save one. I agreed that they are not the correct oven for a user that is primarily interested in pizza making with the odd batch of breads afterward. I agreed that the barrel vault takes longer to fire to achieve the same heat, and had as well agreed that the Pompeii can attain the high temperature quicker and maintain it more easily. (This information was of course based upon observations of my own oven only. I had to take the Pompeii users at their word, but it all seemed to make perfect sense.

The one small point that I disagreed with was the assertion that a higher mass oven could not reach higher temperatures. I felt and still feel compelled to set that record straight. Yes, you would win the wager that the outside of my cladding won't reach 1000F. By the same token, I would feel comfortable wagering that you do not cook your pizzas 6.5" to 8" deep into your masonry. I would argue that the heat used to cook a pizza in 90 seconds probably doesn't come from 6" deep in the masonry. It is the heat stored in the surface of the fire brick and I have no problem achieving 900 to 1000F at least one inch (and probably more)  into the masonry hearth and vault arch (that is where my tc's are located). I assume that you are using an IR gun and are measuring surface temperatures, but that is only an assumption.

It certainly seems to me that there are many out there who consider themselves thermodynamic experts after building one or even maybe a couple of ovens. I certainly don't consider myself one. I try to comment on observations I make, and do not pretend to know the limitations of the other styles.

So finally, I apologize for mostly agreeing with you. I will steer clear of that practice in the future. There is no reason for you to further explain where you are coming from, I think I get the picture.