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Old 10-05-2007, 12:38 PM
Mongo
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Default Smoke past door / Throat Size?

I'm halfway through curing my 50" internal oven and was wondering how much smoke, if any, one should expect out the door vs out the chimney. I'm guessing the hotter it gets (only at 300 now) the better it will draft out. I am concerned though in that my throat is as wide as my opening, about 19 inches, but the depth is only 5 inches. The chimney is an 8" one but it is set back a few inches over the dome opening arch. I'm wondering now if I should have not made it a full 8 inches past the arch or if this matters?

If so I could make some changes to the vent base which would be a pain considering it's a single pour/piece of concrete and rebar or I was thinking I could build a door with a draft option to block off the opening past the vent while firing or perhaps a metal cowl type addition that would come out a little farther into the landing and a little lower to catch and deflect the smoke.

I have a feeling I'm probably alright, just having newbie nerves haha but thought I'd ask the experts before I build or modify anything else.

Cheers,

Mongo
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Old 10-06-2007, 09:29 PM
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Default Re: Smoke past door / Throat Size?

50"? Wow... I have got to see this. A picture is worth a thousand words. Seeing the issue might help with the correct answer.
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Old 10-06-2007, 10:54 PM
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Thumbs up Re: Smoke past door / Throat Size?

Hi Mongo,
the amount of smoke produced is totally dependent on how you set your fire and the wood used (ther size and dryness)
I made 2 stands which hold one end of the very drey western red cedar kindling up in the air with some scrunched up newsprint beneath. Over that O put some larger findling and a few smaller split pieces of hardwood, usuallt river red gum which is very common over here as a eucalypt. I find that I get around 2 to minutes of smoke until the fire really gets underway. If you hane a leraf blower handy, stand back a couple of meters from the oven and aim the nozzle onto the bottom of the fire. If too windy move back or closer untill you see the fire really start to roar, Notice smoke gone. Add slightly larger and larger wood as the fire intensifies which will almost take continuous tending. I think that your 8" flue (diameter I presume) is a little towards the min as I have an 8" diameter one for my 40" Pompeii and that works a treat.
See my vent and chimney at:

http://www.fornobravo.com/forum/21/n...-a-2119-2.html (Neill's Pompeii #10)

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Neill
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Old 10-07-2007, 05:06 AM
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Default Re: Smoke past door / Throat Size?

The vent opening sounds plenty, 19 x 5 = 95 sq inches. Your chimney is 8", so that is approx 50.24 sq inches. What would concern me is you say the chimney is "set back" off of the vent. What exactly does that mean?

For best possible air flow there should be a smooth and gradual transition from one shape to another. If there is not then you will induce turbulent air flow. A small amount is not co critical but a large amount will hinder air flow. I had a similar transition to make, so I cast mine. The throat or transition flows smoothly form rectangle to round. You can see a picture of my plug here;
http://www.fornobravo.com/forum/8/ca....html#post9230 (Casting vent)

Happy baking.
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Old 10-07-2007, 08:02 AM
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Default Re: Smoke past door / Throat Size?

Ok here are a few pictures. It's still a little hard to tell in the photo but the opening is about 5 inches by 19 inches and then slopes back 3 inches above the vent arch as it transitions to a circular 8 inch internal diameter. I did the same calculation you showed about the area (5x19 vs 8" circle) but my thought is a little more depth towards the front of the oven might give the smoke a chance to "make the turn" upwards as about 80 % goes up the chimney but 20% or so seems to work past the door. Of course wind might be a factor?

I think the wood is part of my problem but this oven will be installed indoors (which is why I am so concerned about smoke) and as much as I'd like to use a leaf blower that might not be feasible (although a cool idea haha ya power tools). I'm thinking of adding a metal vent extension with sidewalls on the front of the concrete. I'd cut into it and reshape it or whatever to make a smooth transition back and up towards the chimney.

Only thing I think this might cause for problems is a little more airspace to heat before it goes up into the chimney. Oh, the vent transition is about 13-15 inches high and the chimney is a two foot section.
Attached Thumbnails
Smoke past door / Throat Size?-oven-001.jpg   Smoke past door / Throat Size?-oven-002.jpg   Smoke past door / Throat Size?-oven-007.jpg   Smoke past door / Throat Size?-oven-008.jpg   Smoke past door / Throat Size?-oven-004.jpg  

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Old 10-07-2007, 08:27 AM
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Default Re: Smoke past door / Throat Size?

I think that being indoors will solve most of your problems. Your vent transition seems ideal, we've seen much worse that work. For one thing, there will be no gusts of wind, which cause most of the out-smoking of my oven. Second, you will have a much longer flue run, which will improve things. Third, most of the time you will have the differential between warm indoors and cool outdoors that drives the flue draft.

Just remember, that indoors, you need a source of combustion air. This is not a problem in leaky older houses, but fully sealed and insulated newer ones it may be.
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Old 10-07-2007, 11:15 AM
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Default Re: Smoke past door / Throat Size?

When you light a fire take some rolled up newspaper or what ever and heat the throat opening area first. hold it directly under the opening and let the heat and flames go straight up, just a min or 2. This primes the chimney so to speak, try this and see what happens. Also I think its a good idea if you build your initial fire just past the opening arch in the chamber, this heats up the chimney at first and then you can push this back farther and use it to start your big fire.

My initial thoughts are you are too narrow from front to back for an inside installation with that size oven. Your set back for the throat and pipe is not a concern to me, its just the distance from the outside dome arch to the vent inside. 50" has considerably more volume coming out of it than say a 36" and the vent needs to be sized to accommodate it. That was probably your philosophy for making it wider (side to side) but I think this should have gone front to back. Looking over the FB larger ovens I found the attached. I don't think the drawing is to scale so maybe James can comment on the actual size of the vent opening for this oven.

FB Ristorante130:
Commercial Pizza Oven Specifications
Vent, Arch and Landing
55.4"W x 22.8"D x 29.9"H
Attached Thumbnails
Smoke past door / Throat Size?-ristorante_vent_side.jpg  
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Old 10-07-2007, 01:37 PM
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Default Re: Smoke past door / Throat Size?

OK, pictures help, I misunderstood what you were saying. Vent transition and chimney look good.

Agree with Uno the vent transition should be deeper. One thing you can try. Since the outside of the oven vent is higher than the inside, attach a temporary "hood" at say a 45deg angle from the transion and take it down the same height as the inside oven opening and see how that does. Since it is temporary for test it you can use foil wrapped cardboard, whatever. It may help enough, it may not, but will give an idea of direction to go.
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Old 10-07-2007, 02:30 PM
Mongo
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Thumbs up Re: Smoke past door / Throat Size?

So the consensus is then that the chimney being set back about 3 inches to the rear of the oven is not a problem - just the depth? Would the chimney being directly over the vent improve draft or? I am confused here as I have seen several ovens that vent it back all the way to the center of the dome before going up to a chimney so?

As I see it I could cut the concrete out in the front of the vent and repour a second concrete vent extension there and actually move the chimney over the vent - or I could leave as is but cut a bit of the front of the concrete and then put in a metal extension on the sides and above the landing sloping up as mentioned.

It will be going inside so I have to get the smoke down as much as possible. Had the fire up to 500 today and was careful how I built it and made it bigger and that helped a little and wind was down to a slight breeze and that helps too but there is still 10-20% of the smoke going out the door.

Thanks for all that have commented so far - very useful information as usual.

Mongo
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Old 10-07-2007, 03:36 PM
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Default Re: Smoke past door / Throat Size?

I think the vent setback is OK as long as you have a good smooth path for air flow, that is most important. Most people probably choose straight up because it is easy. It is also best for air flow.
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