6" or 8" chimney pipe Design Styles, Chimneys and Finish Discuss 6" or 8" chimney pipe in the Pizza Oven Design and Installation forums; I have a 36 inch pompei oven. Can I use 6" chimney pipe? Any help on vent size opening?...

[briot]

I have a 36 inch pompei oven. Can I use 6" chimney pipe? Any help on vent size opening?

[papavino]

I have a 36" pompeii, as well. I put a 6" ID chimney on it and it seems to draw fairly well. A little smoke comes out the front, but I think that's due to my flue size. I don't remember what the rule of thumb is regarding flue opening size, but I know it's somewhere on the forum.

[Rastys]

Play it safe with an 8" round stainless flue.
I get absolutely no smoke out the front with one 10' high on a 40" Pompeii.
Also, ensure that you have a good funnelled void to direct the smoke up into the flue.

Rastys

[kebwi]

How does one "finish" a metal flue? I hate the look of a sheet metal flue sticking out of a masonry oven, whether brick, stone, or stucco. I just hate it. Does one built a brick wall around the metal flue just as one would do with a terra cotta flue? What are the recommendations about how far to place the brick from the metal?

If my ultimate goal is a full stucco outer covering, both oven and flue, what would be the best way to build the flue? Metal or terra cotta on the inside? Brick or something else on the outside? How should this be done?

Oh, and just to clarify, Rastys is suggesting 8" on a 36" oven, as in the OP's oven? There is some mention that 6" is enough, such as in the Pompeii directions. Is there any conceivable harm in using a flue that is too big? Say 8" on a 36"?

[christo]

My opinion - yes - if large enough it may affect draw with low heat output, but I don't think using an 8 over a 6 is cause for alarm with the fires/heat from our ovens. Too small (in a relative world) would be a bigger worry for me.

here is a website that discusses it a bit.

Chimney And Fireplace Sizing - A Discussion

Christo

[Rastys]

To me, a smooth stainless flue will heat up quicker and flow quicker with less friction than a square brick chimney. They are also cheaper and much, much lighter than masonry, with a lot less problems.
If you don't like the look of the steel flues, then put in much heavier support strengthened base for a much heavier and bulkier chimney, especially if it is to go through 2 stories.
Hell, what do you want your oven to do, cook well or look good? Yes, they can both be achieved but at a significant cost and engineering requirements.

Rastys.

[kebwi]

Not, not two stories, just a normal little oven. I'll have to think about how to get the weight of the flue off the opening arch somehow.

Thanks.

[Rastys]

kebwi

How does one "finish" a metal flue?

This can be easily achieved with a couple of wraps of chicken wire (or even better a single wrap of 3mm weld mesh) and then some delicate vermiculite cement rendering. Another alternative could include sliding a 10" flue over 6" flue (which would give you a 2" thick coating) and pouring in some refractory mortar or insulation and then undoing the seam and removing the outer sleeve.
Spray the inside of this temporary sleeve with a silicon spray (automotive or sewing/habidashery variety) before installation so that the mortar does not stick.

Rastys

[kebwi]

So, if one wraps a metal flue with chicken wire and then applies a thin layer (1 inch?) of refractory or insulating concrete (which one, refractory or insulating), can the exterior then be stuccoed or will it get too hot and destroy the stucco finish?

[Rastys]

kebwi

I can't see why not. I would also put a thin sand/cement render and then dry it before applying the acrylic render (but this may not be necessary. It would provide additional waterproofing for the vermiculite coating).
Maybe try a small section close to thwe bottom where it gets hottest to evaluate it's effectiveness.

Rastys