Door/Arch Shape Affect on Smoke Draw

[bmoret]

I am finalizing my design and wonder how much the shape of the arch affects the ability for the chimney to draw. I would like to avoid smoke coming out the front as much as possible since the smoke would end up under a covered patio area. I like the look of a flatter, more elliptical shape as opposed to a more rounded shape.

I suppose with a flatter arch, the vent area between the inner and outer arch would need to be wider and with a more circular door, a deeper, narrower vent would be best.


I am sure there are a lot of scientific reasons one may be better than another, and I look forward to that discussion. I am even more interested everyone's actual experience with their oven. What shape is your arch or door , what size is your vent opening, and how well does it draw.? I suppose the chimney is the most important part of the equation, so throw that in there as well.


Thanks in advance

Bill
Spring TX

[Chach]

Im not finished with my oven yet but I'm at that point where I'm at the vent stage and flue building. I've read and been told you need to make the flue gallery like an inverted funnel a place where the combustion gases can accumulate as they go up the flue. I'm guessing most people don't make that part big enough and the smoke fills up and can get up the flue fast enough as there's is not enough room basically to store it as it goes up and out. I not 100% sure I'm correct on this but I hope someone can chime in if I'm right or wrong

[david s]

Preventing smoke out the front is determined by a few design factors.
1. Adequate flue draw. Combined height and cross sectional area (flue pipe diameter)
2. Depth of entry
3. Water content in both oven and fuel
4. Wind in the mouth

Smoke is more likely to escape out the front at start up when the flue is cold and not drawing. This is where the inverted funnel plays a pretty good part. In my design my goal was to make the oven easy to work so a wide entry and shallow entry was most important. To achieve this I designed exceptionally good flow by having a generous flue diameter combined with a tall funnel. The down side is a higher heat loss with the wider door and more efficient breathing unless the oven is doored shut. My inner oven mouth is pretty flat. I think a semi circular one tends to direct the smoke more towards the centre, but unsure which would work best.
Once the oven is pretty hot even a fairly inefficient flue will work well. If
you’re not worried about smoke staining on your decorative arch or a bit of smoke around the oven occasionally don’t worry too much about tweaking the design.