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-   -   Chimney size (http://www.fornobravo.com/forum/f9/chimney-size-18181.html)

Dino69 08-05-2012 05:59 PM

Chimney size
 
Are you able to cheat and place a 6" chimney on a 42" oven? Are there bad smoke issues? Can I make my flue opening larger for more of a funnel effect?

I have found a fairly new 6" duravent, no 8 inchers, on craigs list near my home for dirt cheap. I will buy an 8" if it is the better way to go, but man they are pricey.

Hope everyone had a good weekend.

Thanks,

David

Tscarborough 08-05-2012 06:31 PM

Re: Chimney size
 
Flue size should be around 10-15% of door opening size in square inches. So, for example, if your door is 17x10=170, your flue should have 17 to 26 inches of cross section. A 6" round flue will be 3 squared times 3.1416=28.27 which would be fine. What is your inner arch opening size?

Gulf 08-05-2012 06:47 PM

Re: Chimney size
 
Quote:

Originally Posted by Dino69 (Post 136155)
Are you able to cheat and place a 6" chimney on a 42" oven? Are there bad smoke issues? Can I make my flue opening larger for more of a funnel effect?

I have found a fairly new 6" duravent, no 8 inchers, on craigs list near my home for dirt cheap. I will buy an 8" if it is the better way to go, but man they are pricey.

Hope everyone had a good weekend.

Thanks,

David

I think that most would say splurge for the 8". Some would say increasing the height of the 6" would offset the decreased diameter. Increasing the "flue for more of a funnel effect": (If you are meaning deepening and widening your entry) would take you to a height that would probably make buying any kind of stainless flu unnecessary. That would however, make working the oven, more difficult due to the extended reach. That is what most would say. I intend to find out for myself as I have built a large entry and flu. I have a few work arounds in mind but nothing that I can relate to you in experience. For the moment and from my personal experience my advice is to buy the 8" Dura vent :). There are no cost or time savings in shortcuts :D.

david s 08-06-2012 02:15 AM

Re: Chimney size
 
I think most builders would shoot for an 8" flue for a 42" oven. Because the front flue design draws also from the outside air and you need the efficiency at a lower temp especially at light up, it needs to be bigger than you would think. Once the temperature is up a fair bit it becomes more efficient. It is also not just the size of the door that needs to be considered, but the size of the oven chamber as well.A 42" oven has about 60% more volume in the chamber than a 36" so thats a lot more smoke to vent. Try going to your local sheet metal worker and get a quote to have one made up from 0.55 mm 304 stainless.

Dino69 08-06-2012 06:01 PM

Re: Chimney size
 
Thanks for the replies, gentlemen. All seem to be valid points.

Tscarborough, my inner arch is a 20.5" wide by 12.75" high sort of semi-circle. It was going to be 20" wide, but my outstanding masonry skills decided it should be 20.5". So I would have an area of about 165". So I would need 16.5" to 24.75". What size is your oven, opening and chimney?

Gulf, I agree with the "no cost or time savings in short cuts." I would rather have it done correctly. I do not want smoke pouring out the front of my oven. Although, I remember a few on here who do like the slight soot stained front look. It is really great to be able to ask people, way more knowing than myself, a few questions when they do arise.

david s, that is a great idea. I will call some metal fabricators tomorrow and get a bid. The inside volume of the oven is pretty big. Bigger than I thought it would be. I am not small and I was sitting in it yesterday sponge cleaning mortar. I imagine it would create quite a bit of smoke.

Hopefully someone will be trying to sell an 8" ID online at some point. I do love a good deal.

David

Dino69 10-26-2012 07:38 AM

Re: Chimney size
 
david s,

Just wanted to thank you for reminding me about calling a metal fab shop for the chimney. I have used a shop near me in the past but for whatever reason I never thought to give them a call for this project. Too much tunnel vision on the oven at times I guess.

It saved me a bunch of $. I could have went even cheaper with the refractory flue tile but I like the look of the SS.

A friend and I split a roll of ceramic blanket and I stuffed the chimney myself. I was at 850 degrees for 4 to 5 hrs the other day and the chimney was barely warm a few inches up from the base on the outside. Everything else was cold.

Thanks again. It was much appreciated.

David

david s 10-26-2012 12:26 PM

Re: Chimney size
 
If anyone else reads this thread you can ask your sheet metal guys to taper the flue pipe slightly so that a second section can fit onto the first if you want to go taller. It is a simple job for them, but beware, they are likely to pass the work over to an apprentice who is inexperienced and there is then a greater chance of stuff ups. I've been down that road.


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