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-   -   Vent/chimney or not? (http://www.fornobravo.com/forum/f2/vent-chimney-not-2112.html)

readie 06-15-2007 09:40 AM

Vent/chimney or not?
 
Is it important to have a chimney/ vent in a brick iglo shaped oven? I wasn't intending on putting one in but would value others opinions on the matter before I make a mistake?! :confused:

dmun 06-15-2007 10:08 AM

Re: Vent/chimney or not?
 
Smoke in your face? I don't think so. This is supposed to be fun.

readie 06-15-2007 10:20 AM

Re: Vent/chimney or not?
 
Hmmm, good point.

RTflorida 06-15-2007 11:11 AM

Re: Vent/chimney or not?
 
Not to mention the 'draw', a properly placed and functioning chimney helps in the cyclonic air circulation - feeding the fire fresh air;which leads to larger, hotter fires. You will use less wood by heating faster and achieving a more efficient burn, AND no smoke in your face.

RT

CSWolffe 06-15-2007 03:23 PM

Re: Vent/chimney or not?
 
Is there a migic formula for a 'properly placed and functioning chimney'? diamater of flue compared to dome opening, or distance back from front of landing arch?

RTflorida 06-15-2007 05:56 PM

Re: Vent/chimney or not?
 
CS, don't know of a magic formula; but I will share what I've learned from countless hours of reading this forum.

Size - There are recomended flue/chimney sizes based on your oven size. Check the Pompeii instructions. I built a 36" oven, I believe the recomended flue is the equivelent of an 8" round pipe. Remember, there are different shapes - the round Duratec like pipes (which I used) or rectangular flue tiles. compare the square inches of the sizes when choosing the style/size for your oven. I actually only used the 6" Duratec pipe on mine, I wanted my entry/landing/flue area a certain size; so using the recomended size would have thrown off my plans...I took a chance with the smaller size and the results have been fine. I get a bit of smoke that comes out the entry if I foolishly throw too much on the fire during start up. No big deal, I've learned not to rush fire building.

Placement - As a general rule; you do not want the flue/chimney exiting too high up the dome. Too much immediate heat loss. You lose the main benefit of the dome (the hot air rising, then swirling down the sides to the hearth).
James has actually posted diagrams of how an oven circulates. Sorry, you will have to search for them.
From many posts I have read from those with far more experience than you and I, placing you flue/chimney just outside of the dome in the entry/landing is the best placement. You get the best 'draw' of fresh air and you are not sucking the hot air off of the dome top, disrupting that beneficial swirl.

I hope this helps, remember this is not an exact science. Much or the design and execution can be changed or adapted to fit your budget, size/space requirements, and aestetic preferences. Your not ready to build until you've gone 'bug eyed' from reading this forum:D

Good luck
RT

maver 06-15-2007 06:31 PM

Re: Vent/chimney or not?
 
RTflorida:
Placement - As a general rule; you do not want the flue/chimney exiting too high up the dome. Too much immediate heat loss. You lose the main benefit of the dome (the hot air rising, then swirling down the sides to the hearth).


This formula is oven opening no more than 2/3 dome height. My 18" high dome has a 12" high opening. You can retain a little more heat with a lower oven opening than 2/3, but usability issues (like fitting a turkey) can become an issue. There are formulas for fireplace flues and openings that you can read about if you google for Rumford plans, but these do not correlate directly with a masonry oven. I think rather than a formula for flu size for an oven the suggestions here on the forum are based on what others have found effective or perhaps based on observations of working ovens. James, DMUM, Jengineer, does this sound right?

wlively 06-15-2007 08:06 PM

Re: Vent/chimney or not?
 
I have to agree that a vent is needed. Mavers dimensions sound good to me. I think the best rule to follow is make the opening the smallest you can be happy with because smaller means less heat loss.

I thinks James examples of open vents are a good option if you like the open accessible look.

Mine is a 42 inch. I have a brick arch entry with a 12" wide x 4" rectangular opening, that has a cast transition to 8" Duratech pipe. It draws great. The only change I would make would be to widen the rectangular opening 2 inches or so to more effeciently scavenge the smoke, when it is heavy.

Another good thing to think about is how the air is going to flow. Keep the transitions smooth to reduce turbulance, the faster the air is moving the lower the air pressure. I also keep the air moving upward, the roof of my entry is sloped upward, to help funnel the smoke.

dmun 06-15-2007 08:15 PM

Re: Vent/chimney or not?
 
Flue size by code is a function of the fireplace opening, and keeps growing. My house from 1910 had a 8 inch square flue tile (and draws great, through three heated floors) for a medium sized fireplace, most midcentury or later fireplaces had 8 by 12 flue tiles, and some versions of building code call for a 12 by 12 flue now.

Brick ovens have such small openings that you could probably vent it through a six inch flue, but more area is useful in pulling that draft for fire starting.

RTflorida 06-15-2007 08:35 PM

Re: Vent/chimney or not?
 
I agree, I could have and probably should have used 8" instead of 6". I simply build my fires just inside the dome and push them back once it starts to roar. Not piling too much on initially is the key for me, and makes logical sense. I was too impatient at first. It really draws well once the 'real' wood lights.

Just goes to show that the general rules are adaptable to your specific needs/plans. Even if draw were not an issue....I would still put in a chimney, smoke in the face is not good.


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