draw and flue

[cecora]

While looking at all of the pictures I notice some show soot build up on the outside of the oven face indicating improper draw I would think ? Is there specific specs any where to insure this does not happen ? If you build your WFO indoors that would be a major problem. Thanks in advance!

[david s]

The cross flow design of the Pompeii style oven produces excellent chamber circulation and efficiency, over an updraft system like that employed in a standard fireplace.
Because heat rises by convection and carries the smoke with it, The flue in a cross draft design does not act well when cold, it must be given time to heat up.There are a number of things that produce a smoky oven.

1.Using wet or green wood
2. Firing a new and wet oven.
3. Overloading the chamber, particularly at light up.Start with a really small fire.
4. Insufficient draw from the flue
5. windy conditions at the mouth interfering with smooth flow.
6. excessive bends in the flue. Bends should not be flatter than 45 degrees.

The larger the oven the more power is required from the flue to provide sufficient draw.
Ovens up to 28' internal diameter should have a 5" flue pipe, up to 36" a 6" and up to 42" an 8", over 42" a 10"
While the flue diameter is important the height also has an influence on draw, but not as much as the diameter (or cross sectional equivalent if a square or rectangular chimney)
A smooth flow to the base of the flue or chimney is also important. An inverted funnel form provides a much improved flow.

[buckeye_brian]

Michael Angelo was often asked, "When are you going to start carving on that stone? All you do is look at it." He would reply, "I am carving it in my head so I know what to do when I pick up the chisel and hammer."

For the next few evenings I will be Michael Angelo with a bourbon in my hand...building the vent / flue opening in my head...

[Michele Enrico]

Michael Angelo was often asked, "When are you going to start carving on that stone? All you do is look at it." He would reply, "I am carving it in my head so I know what to do when I pick up the chisel and hammer."

For the next few evenings I will be Michael Angelo with a bourbon in my hand...building the vent / flue opening in my head...

My friends ask me all the time how is the pizza oven coming. Now I know how to reply because this is all too true.

[david s]

Interesting that you mention Michelangelo. Regarding vermicrete, it can be used to create an excellent material, suitable to carve, because it's so easy to adjust its strength. As an ex-secondary school art teacher I've had students carving lots of these, yes the water drains out the mouth. The vermicrete is easy to both carve and add on other bits to build up.
Michelangelo also used to describe his MO as "I am releasing the figure from imprisonment".

[cecora]

David S thank you...Right. like the 2' x 10' rule when building a chimney on a roof for proper draw. Thank you for the numbers. Very helpful. Looking forward to this build. Will post progress when I get started.