Help with vent floor size

[david s]

Re: Help with vent floor size

"Also, it seems reasonable that the vent funnel area should be at least as wide as the flue. I have drawn a 7.5" depth of funnel area for a 6" flue. Is this too much? I cant find a definite answer in the forum or plans. Many suggest to use an 8" flue for a 36" oven instead of the plan recommended 6". "

I believe the advantages of a shallow vent area outweigh the difficulty in building it. It is possible to make the flue gallery only as wide as the flue pipe itself, by incorporating decent funelling in the design. This then leaves you with an oven that is much easier to work, particularly if you make the entry fairly wide as well. My oven entry is only 5" and the same size as my flue pipe. The oven is a dream to work.

If you plan on a 6" flue you can simply make the flue taller to increase the draft. That way you also get the advantage of a shallower entry.

[texman]

Re: Help with vent floor size

Thanks Chip. Need to do more drawing to get my head wrapped around this.

[mrchipster]

Re: Help with vent floor size

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Is there an optimal distance from center?

Also, it seems reasonable that the vent funnel area should be at least as wide as the flue. I have drawn a 7.5" depth of funnel area for a 6" flue. Is this too much? I cant find a definite answer in the forum or plans. Many suggest to use an 8" flue for a 36" oven instead of the plan recommended 6".

I have attached two jpeg drawings to hopefully demonstrate my variances for the inner arch placement.

Bricks, tiles, and mortar are being delivered today. Thanks for any and all advice on this.

I pushed my flue arch even further into the dome using bricks that reach back into the dome as they go up. The outside of the brick was almost even with the outside of the dome at the first course and reached back into the progressively further in each chain.

This method significantly reduces the dreaded teardrop effect.

Use this thought when building the inner arch.

The inside edges of the brick are defined by the inner radius of the dome. The bricks of the inner arch will take on a shape resembling a pointer with the lower side following the inner radius of the oven.

And the upper surface of the pointer being defined by a vector radiating from the center of the oven.

Read the post Octoforno for a much more detailed description and photos.

My post Chip's 42 in Minnesota also.

Chip

[texman]

Re: Help with vent floor size

I am trying to decide the proper distance from center of oven to inside edge of the inner arch opening. I am building a 36" oven and an 18" width for inner arch. The inner arch opening can be "pushed into" the oven as close as 13.5" from the center of oven or "pushed out" so far as to not lose any of the actual floor area (see the attached 37.5 plan) So, in my 36" oven that gives me a variance of as close as 13.5" from center to 18" from center.

Is there an optimal distance from center?

Also, it seems reasonable that the vent funnel area should be at least as wide as the flue. I have drawn a 7.5" depth of funnel area for a 6" flue. Is this too much? I cant find a definite answer in the forum or plans. Many suggest to use an 8" flue for a 36" oven instead of the plan recommended 6".

I have attached two jpeg drawings to hopefully demonstrate my variances for the inner arch placement.

Bricks, tiles, and mortar are being delivered today. Thanks for any and all advice on this.

[gjbingham]

Re: Help with vent floor size

Thanks Les and Christo. I think I'll follow suit.
George

[Les]

Re: Help with vent floor size

making the arch of the oven opening slightly lower, say a half inch or so, than the height of the vent.

George - that's what I have planned, I'm lowering my decorative arch to accomplish this.

Les...

[christo]

Re: Help with vent floor size



I made my decorative arch about an inch lower than the vent arch - even lower a the edges to accomodate my lights.

I'm not sure if that is why - but I have no soot on the front face of my decorative arch after at least 12 fires......



I beveled all of the bricks at 45 degree angles leading into the opening for the vent. It could also be the really cool teracotta vent transistion idea I stole with pride from DMUN Dave....

Good luck!

Christo

[gjbingham]

Re: Help with vent floor size

Great response guys. Carlo and Les caught my original concern and the responses confirmed the answer I came up with. I'm way past the point of no return now (barring a complete collapse). I've opted to build the dome first and deal with the vent and oven opening later.

The recommendation for a 4 X 8 vent was also interesting. I was lying in bed last night thinking that it might help increase the draw of the oven by making the arch of the oven opening slightly lower, say a half inch or so, than the height of the vent. From the decorative arch in front of the oven to the anterior edge of the vent, build the arch 12 inches or so high. The actual vent itself framed in at 12.5 inches back to the oven dome opening.

I'm not sure if this is a clear description. Maybe it's a dumb idea. It seems like a slight rise in arch height from the oven opening back to the actual dome would speed the draw of the chimney and minimize smoke sneaking out the front during the early heating process.

[RTflorida]

Re: Help with vent floor size

A few metres??? Seriously, that sounds like it came from the arctic circle foundation guide. I'm originally a northern boy, 3-5' frostlines I am familiar with.

To me "a few" means 3 or 4 = 9-12'.....good golly, its gotta get damn cold and stay damn cold (arctic circle???) for far too long for my tastes. Does the ground ever actually thaw completely?
Maybe 10 years away from cold and snow has affected my memories and what I thought I knew. I'm just amazed by an inhabited area having a "few metres" frost line.

[Les]

Re: Help with vent floor size

Carlo, extremely helpful to add the picture to it. Just to add some clarification, I have 4 inches between the landing and the existing front arch. My landing begins at the front of the hearth.

Les...

[Les]

Re: Help with vent floor size

I hear ya David - and THAT's funny!!! I think what they are implying is that two feet short of magma is best...

Les...

[dmun]

Re: Help with vent floor size

Here is a quote from this link:
The Chimney

Here is another quote from that link:

masonry chimneys need a foundation that extends below the frost line, which is a few metres below grade in most of Canada.

A few? Two? Three? Half a dozen? Hell, why not dig down to bedrock?

[james]

Re: Help with vent floor size

That's it.
James

[biondoli]

Re: Help with vent floor size

I added Les measurement to the picture he has on the web so we can graphically confirm our understanding and use as guide. Hope this helps, check the link below.
Carlo

[Les]

Re: Help with vent floor size

George,

I think we are mis-understanding your question. I interpret it how much space you need from the dome opening to your landing area. If that's the case, here are my numbers.

I have 12 inches of landing area. I am allowing 4 inches for decorative brick. My front arch brick is 5 3/4 inch, the vent opening is 6 inches and the back arch is 4 1/2 inches. All said; from the front of the landing to the inside of the dome will be 32 1/4 inches.

Les...