Large huge oven

[quintin]

Hi, I am an architect who is obsessed with questioning things! and I am about to build my own Pompeii oven. The dome will be 2m diameter. I have started to question the following:

1- Why creating one door and have the ash from burnt logs dragged all over the floor, when one could create a an adjacent burning chamber with separate door that can be fully sealed if constructed correctly?

2- Why using bricks on large domes in the Europe and the US when dome building masters are scarce Arab dome builders? Why not use pumice with 1:5 ratio and enforce it with natural materials?


3- Why is it that we build small ovens rather than large ones? why stick to the 4-" that are everywhere???


4- Why do we build ovens with chimneys at the top of domes when we all know the heat will go up without circulating through the internal dome?


5- Why don't we use louver shutter for the chimney shaft top reduce the heat escape, therefore controlling temperature?


6- Why is it that we build the arch above the door without a tie to the dome? Doesn't it separate? I have seen it separate!!



Any feedback will be appreciated. 

[downunderdave]

1. A lot of extra work and potential heat loss with that idea. Some builders make an ash drop which is a slot near the entry, but usually after using the oven decide it wasn't worth doing. There is way less ash to clean out than you would think. I only remove ash after about 4 firings, certainly not after each one.

2. I presume your question relates to bricks vs casting. If you prefer to cast then you don't want a low density casting that pumice would give you. You need a high density conductive material that will store heat. Pumice acts as an insulator and also reduces strength, both characteristics you don't want on the inner dome.

3. You won't be cooking two pizzas in a 2 m diam oven. Fuel consumption is roughly directly proportional to the volume of the chamber so a large oven eats tons of fuel. A 15% increase in diam is something like a 70% increase in volume. Doubling the diam, say going from 1 m to 2m is an increase of 8x. Most builders have ovens for domestic use rather than cooking for the whole village.

4. You get better draw if the flue is in the top of the dome meaning less smoke at start up, also there's no entry to have to work past. Downside is that circulation is poorer and lots of heat is lost up the flue. Definitely not a good idea for a large oven.

5. You don't need flue control for a front flue cross draft oven because the flue is isolated from the chamber.

6. Some builders deliberately create a heat break here to reduce heat loss. You can do that or not bother, it won't make that much difference.i prefer to have an expansion joint between the flue gallery and the outer decorative arch so the inner oven parts can freely expand without stressing the decorative arch or outer shell.

[diggerjones]

Mines a conventional pompeii oven. 40" wide. I cooked a 48 kg pig in mine, how much more would you want to cook.??

[oblertone]

There are domes in Pompeii greater than 2m in diameter, but there are no domes in private homes there either. The larger domes are commercial, meant to feed the many and rarely allowed to cool. That is an important consideration as heating a 2m dome from cold is going to take time and fuel, large quantities of the latter.
Brick is plentiful and cheap as the UK stands mainly on clay from which bricks are made, why look elsewhere to solve a problem that doesn't exist.
As to heat control, one of the joys in using your own WFO is learning how to manage the fire for the best effect. A regulated flue may well assist, but closing it would mean more smoke out of the front of the oven, which is not comfortable for the user.
I'm sure you are aware of the critical dimensions recommended for a home built WFO i.e. a ratio of 63% between the door height and dome height (internally). This allows for adequate heat transfer from the products of combustion into the dome fabric before the exhaust gases pass into the lower entry arch. That is why most WFO's have the flue in the entry arch and not in the dome proper.

That being said; you are an architect, let's see some plans, maybe you'll have a different take on how to make one.

Paul

[jrb103]

My oven is 1200mm diameter pompeii and when cooking pizza i could get probably 8 pizzas or more in at a time but you cant get them in / out quick enough most i have managed is three at a time put last on in take first out 90 second cooking time max. Then when cooking in after it has cooled down if baking bread you want the steam to help with the baking in a 2m oven you would want to bake about 50 loaves at a time.

[downunderdave]

Jul 12, 2016 10:16:49 GMT oblertone said:

There are domes in Pompeii greater than 2m in diameter, but there are no domes in private homes there either. The larger domes are commercial, meant to feed the many and rarely allowed to cool. That is an important consideration as heating a 2m dome from cold is going to take time and fuel, large quantities of the latter.

Paul

That's not quite accurate. When visiting Pompeii in 2010 I was on the lookout for ovens and saw at least 3 in private homes. They were all small ovens no bigger than 24" in diam and they all had their flues in the centre of the dome (updraft) like ancient Roman kilns. Having built my first oven this way in '07 I was interested as I thought all ancient Roman ovens were built with front flues (cross draft). The two great advantages of a flue in the centre are firstly, no entry to have to work past so access is better. Secondly, the updraft system draws much better at start up so you woulsn't be smoking out your house. As you pointed out Paul, the larger cross draft ovens probably never cooled down so the flue was always warm. The main disadvantage of a central flue is that they are less efficient and use more fuel, however their smaller chambers more than compensated for this problem because fuel consumption is directly proportional to chamber volume.
Dave