Continued Design Ideas

[david s]

Re: Continued Design Ideas

I know these figures work in fireplaces but they seem way to small for WFO. Both of my ovens have probably been closer to 80%. My current oven is 42" with an 8" flue. It has an arched door 18 inches wide and 8 inches tall. That comes out to about 112 square inches.

10% = 11.2 square inches
15% = 16.8
20% = 20.4

The 8" flue has an area of 50.24 square inches. What you guys are suggesting is actually a giant constriction in the transition. Just to be the same area as the flue the opening would need to be nearly 45%. I'm sure the numbers are a little better for a higher domed oven with a door big enough for an SUV, but not much. IMHO the opening should be as wide as the door and at least 6 inches deep if you want to get all the smoke on startup.

Your oven must have an extremely low dome for it to have a door only 8" high.
My 21" oven has a 5" diam flue which works out to 20% of the oven opening, with good funelling to the flue I feel it is correctly flued, but I've seen plenty that are not.the evidence is the large amount of black soot at the entry.

[shuboyje]

Re: Continued Design Ideas

I re-read and see you guys are talking about flue size and not the size of the bottom of the vent transitions as I originally thought. Makes a lot more sense now, and the numbers do seem to line up for hemispherical ovens.

42" oven = 21" dome height

63% x 21" = 13.23"

13.23" x 18"(common door width) = 238.14 Square inches for a rectangular opening

20% = 47.628 Square inches

In standard sizes that rounds up to 8" round, the common size for a 42" oven. Like the 63% ratio, door geometry is a factor, as is dome height as shown in my last example.

FYI my dome is 12.75".

[Tscarborough]

Re: Continued Design Ideas

The rule of thumb is just that. The important concept is air pressure. If you have a large oven opening, a small flue and a tall stack, it may well work. If you have a large interior opening, a large flue but an even larger outer opening it may well smoke. It all has to be in sync.

[david s]

Re: Continued Design Ideas

I re-read and see you guys are talking about flue size and not the size of the bottom of the vent transitions as I originally thought. Makes a lot more sense now, and the numbers do seem to line up for hemispherical ovens.

42" oven = 21" dome height

63% x 21" = 13.23"

13.23" x 18"(common door width) = 238.14 Square inches for a rectangular opening

20% = 47.628 Square inches
In standard sizes that rounds up to 8" round, the common size for a 42" oven.
Like the 63% ratio, door geometry is a factor, as is dome height as shown in my
last example.

FYI my dome is 12.75".

So your oven dome is 21" high internally or 12.75"? and your door is only 8" high? Still doesn't seem right to me, but if it works, what the hell.

[shuboyje]

Re: Continued Design Ideas

No 21" was an example for a hemispherical 42" oven, just showing the numbers do work better for a hemisphere. My oven is 42" with a 12.75" dome height and an 18" x 8" arched door.

[david s]

Re: Continued Design Ideas

Ah, OK, now I get it. thanks

[clofgreen]

Re: Continued Design Ideas

Thanks all for the input about flue size.

The weather was great Saturday so decided to build the vault. It went up fairly quickly. I built a guide to make sure my arch was uniform.



After four courses...



I cut out another guide, attached some old fence slats...



and finished it with daylight to spare.



Because the bricks were tapered, I was able to maintain a 1/16 inch inner joint and 3/16 outer joint. The home brew mortar worked great. Smooth as silk. I can't say enough good things about the information available on this forum.

[brickie in oz]

Re: Continued Design Ideas

Nice...... and all bonded too..

[clofgreen]

Re: Continued Design Ideas

I finished laying all the firebrick and have only used 1/2 bag of silica and less than a 1/4 bag cement, lime and fireclay. I've read that I can make face brick mortar by using this mix: 1 cement + 1/2 lime + 3 sand. Can I use the 70# silica sand for this mix or do I need to use sand specifically made for mortar?

Second question: I'm ready to make my vent and can get a 55 pound bag of castable refractory for $35. Will one bag be enough to cast this vent?



Third question: The place that sells the refractory told me I do NOT need to use stainless steel needles in this cast. Are they right?

[david s]

Re: Continued Design Ideas

I don't know how much weight you are intending to put on top of the vent, but 2" is overkill IMO. I would think 1" would be plenty. SS needles are not necessary, I use them, only because I assume it will make the resulting castings stronger. If you want to you can easily make the depth of the vent less than the diameter of the flue, without compromising the draw of the flue or the funneling effect for efficient smoke removal.. This enables you to have a shallow entry for better workability of the oven?
Working outside a corrugated cardboard form held together with plenty of gaffer tape should produce a suitable form to cast over, and easy to remove.

[clofgreen]

Re: Continued Design Ideas

I've been curing the oven this past week, today being the last curing. I also started adding another layer of perlcrete that you can see steaming in the photo.



After about five hours I decided to push the temps and see how the oven performed.



Three small cracks formed but that's about it.



I heated it until the vault turned white. Great draft and very little smoke. I think tomorrow is pizza day.

Next step, building the vent and flue. I'm thinking of casting the flue as well as the vent.

[clofgreen]

Re: Continued Design Ideas

Had a Christmas Eve Day pizza party. The weather was great - sunny and 40 degrees F. The oven performed mahvelously. It got up to temperature in 1 1/2 hours and cooked pizzas in two minutes flat. Here's a sampling of the dozen or so that we made. After the pizzas were all cooked and everyone stuffed to the gills, we still had four dough balls left so we made cinnamon desert pizzas.



Here's the last pizza we cooked. I let the fire die just to see how the oven cooked with just coals. It took three minutes.



I have a roast in there now and plan to bake potatoes a little later.

I have to say that building this oven was a very very good thing. Everyone loved the pizzas even though we made the dough from old general purpose flour that puffed up more than we would have liked and our ingredients were just things we had in the house. Still, we're from the U.S. mountain west and not especially discriminating when it comes to pizza so we're easily pleased. I encourage anyone thinking about building one to go for it. You won't regret it.

Now my reflections on dome vs. vault.

I was reading in the Pompeii oven plans this morning about the dome vs. vault and have to say that I'm not convinced at all with the argument being made for the Pompeii. If anyone is considering making a vault I encourage it. It was fairly simple to build which was key for me since I have zero experience building this kind of thing. It heated fast, cooked fast and I could cook four pizzas at a time and even though I had to turn them to cook them evenly I know the same happens in the dome oven.

Thanks to all who have contributed to this wonderful forum and especially those who responded to my unending questions.

Merry Christmas, Happy Holidays and have a wonderful New Year.

Craig

[brickie in oz]

Re: Continued Design Ideas

Nice, you make free form pizzas like I do....

[Derkp]

Re: Continued Design Ideas

Looks great Craig, keep up the good work and I hope the weather continues to be cooperative with oven completion tasks. My boy is now 4 days a week at snowbird operating lifts, mabey I will try to stop by after skiing some day.

Derk

P.S. It would appear that you have joined the WFO pizza lovers completely, the roast and spuds will be great, I'm sure.

[Lill Dave]

Re: Continued Design Ideas

Dude, save a little cash and buid a Pompaii. The work involved is signifigent for both designs and you might as well have the right oven.
My first oven was that style , it works , but the pompaii oven that you can get the plans from this site is far better.
All you need is a 7.5'' 35 buck dimond blade and saw.
You can jig up for all the 4.5in cuts and it is real easy .
The plans ar free