Is it possible to 'over-flue'?

[GianniFocaccia]

My dome is almost completed (last two courses and key) and I have started to think about vent/flue design and dimensions. I guess the common rule for fireplace flue size crosses over to WFO's: flue 10% of fireplace/door opening.
For my 39" Pompeii this would mean a round clay flue liner with an 8" inside diameter.

I know it is critical not to underflue a WFO so that it breathes properly and doesn't allow smoke out the front of the oven. Is it possible to build a vent and flue that draws too aggressively? Anyone run across this?

Thanks in advance.

John

[brickie in oz]

Re: Is it possible to 'over-flue'?

Ive never come across a flue/chimney that draws too aggressively.
Ive built lots of fireplaces and brick chimneys (they dont use flue liners here) with lots of different sizes and specs from owners and never seen this problem.

[GianniFocaccia]

Re: Is it possible to 'over-flue'?

Thanks, Al.

I have trying to source an 8"id round clay flue liner here in SoCal, but was told this is not a common fireplace size therefore will be difficult to find. He did, however carry a 12" round clay flue tile that he was selling in 1' lengths at $25/per foot.

[brickie in oz]

Re: Is it possible to 'over-flue'?

1' lengths at $25/per foot.

Thats expensive.

Couldnt you cast one from castable refractory concrete cheaper?

[david s]

Re: Is it possible to 'over-flue'?

I've seen plenty of ovens with flues that are inadequate in diameter or design. The evidence is the black sooty staining on the front of the decorative arch. With the front flue independent of the oven it is virtually impossible to over flue it because excessive draw will simply suck more air from the front rather than the fire. The other important design feature is decent funnelling into the bottom of the flue pipe or chimney. The Victorian house I grew up in had six fireplaces fitted with very tall chimneys and adjustable flue dampers to prevent excessive heat loss up the chimney once the fire was going well.

[GianniFocaccia]

Re: Is it possible to 'over-flue'?

Brickie,

You're right. The very next place I called quoted me $14 for each 1' section of 8x13", also from Superior Clay. I think a 55# bag of castable is around $70, and yes, I could form a killer vent mold with wood I have in the garage. A thought, for sure.

Thanks for the input, David. Makes sense that an aggressively-drawing flue would also draw from the front-side rather than suck the heat out of the oven. Now... what if the flue is too large and doesn't create the minimum pressure needed to keep the exhaust on track and going where it's supposed to go? Is this possible?

John

[Tscarborough]

Re: Is it possible to 'over-flue'?

Just imagine the case of an oven with no flue, and that would equal too much flue, so the answer is NO, you can not over-flue an oven. A fireplace, yes, but the dynamics and requirements are different.