Smoke Billowing Out of Opening Instead of Chimney!

[Kmelrose89]

Gentlemen,

I lit my first curing fire in my home-built oven tonight. Much to my horror, most of the smoke (and heat) were billowing out of my front arch opening, and not the chimney!

Background Info:

Pompei style oven--64" in diameter, 31.5' dome height, 20.25" front arch height.

I was very careful to build the front arch and the dome according to the golden ratio--exactly 63%.


What I think is happening is that my chimney opening is too small--it's 6" by 4", which I think may be too small considering how large my oven is.

I wanted to check with everyone here and rule out: 1) is the chimney in the correct location 2) is the front arch too high despite the golden ratio? Maybe my dome is too shallow and the front arch should be lower?

My biggest question is, assuming the front arch is the right height and the chimney is in the right spot, is: if I open up the chimney, how big should it be?

Thank you to everyone in advance! Pictures attached!

[purplehaze]

My oven is 42" in diameter with an 8" chimney. I only get the occasional wisp of smoke out of the front on a windy day. I remember seeing a chimney calculator on this site someone was working on.

[jimkramer]

You can also make your chimney taller, which will create more draw (I think.) I have a 42" oven and a 7" diameter flu, instead of 8. Lots of smoke comes out the front when I'm first lighting the fire. After the fire gets going, it all goes up the chimney, so it really doesn't matter.

[UtahBeehiver]

You are probably right on the chimney size. For a 64" you probably need at least a 12 - 14" ID or larger vent. Some possible help would be to make sure the chimney you have is drafting. Start a small fire under the opening to make sure it is drafting then you can push the fire back into the dome later. Since you are curing you should go really slow. Unfortunately, a larger chimney is needed.

[david s]

You give your opening to the chimney as 6” x 4” which is 24 sq in. For an oven your size a flue diameter of at least 10” would be required which is 75 sq in, so yes your entry is inadequate, but it is the chimney cross sectional area, in combination with its height above the entry, that is more important to provide the power to draw smoke out of the oven.
All new ovens are notorious for being smoky especially at light up, until all the moisture has been driven out. So although your design is inadequate the situation will improve with more firings.

[fox]

I don’t think it is that unusual for new ovens to smoke out the entrance, the ones that I build normally take a few days of fires to start behaving but really only become smokeless when totally cured.
Good luck with yours.