Need advise on what chimney/flu combination will draw best?

[Wheels1974]

I have just completed the front arch. The vent dimensions are 12 inches by 4.5 inches. I would of liked to go 12 inches by 6 inches but I couldn't as this would of extended the distance from the inner arch to the front arch and I already have it 14 inches long which worried me at first until I had a guy come over to look at it. My initial concern was because there is 14 inches from the door to the front arch I was worried if this would of posed a problem when trying to start the fire due to lack of oxygen but I was told I had nothing to worry about.
I'm not sure whether I will make a funnel and then attach it to a 8 inch round flue or I might make my own funnel/flue in one piece out of stainless steel which will obviously be 12 inches by 4.5 inches from beginning to end.

My query is, what chimney/flu combination do you all think would draw best?

P.s. Also if anyone can tell me, is there a general size a vent should be on WFO's, because I would love to know if there is?

Regards
Dean

[nissanneill]

Re: Need advise on what chimney/flu combination will draw best?

Hi Dean,
I hate to be the one with bad news, BUT I feel that you are going to get considerable smoke out your front arch with your chimney void being the size and location that it currently is. To answer your question, I would certainly use an 8" stainless flue with a funnel shaped void to capture and funnel the smoke in the required direction.

I'm not sure whether I will make a funnel and then attach it to a 8 inch round flue or I might make my own funnel/flue in one piece out of stainless steel which will obviously be 12 inches by 4.5 inches from beginning to end.

An 8" flue has 50.3 sq inches in area whereas your 12 x 4.5" has a surface area of 54 sq inches which would allow more to pass through.
My chimney void is 620mm wide x 400mm deep funneling the smoke into n 8" galv flue 3m long. The back of my oven entry arch is also beveled to help the smoke to change through the 90˚ direction.
I'm not sure as to what your are asking with regards to

is there a general size a vent should be on WFO's

Neill

[Wheels1974]

Re: Need advise on what chimney/flu combination will draw best?

Neill,
When I mentioned "Is there a general size a vent should be" I meant are there formula's or a method to work out how big a "vent or void" should be in comparison to each individuals WFO. For example a 36 inch cooking circumference WFO would require a smaller void then lets say a WFO with the cooking circumference of 42 inches I would imagine.

P.s. Damn your void is wider then my whole arch. Dont you have trouble getting your WFO to hot temperatures?

Regards
Dean

[nissanneill]

Re: Need advise on what chimney/flu combination will draw best?

No Dean,
I can honestly say that I get the dome white within an hour and then spread the coals around the hearth and let it absorb the heat for another half hour.
Yes, I need to reach a little further into the oven to light it but have experienced no other problems. I guess that is what you get when building your front arch and void before the dome which I found much easier to get the transition done.
This is of course a debatable point but others prefer to build their dome and then try to get the transition to the void worked out.

Neill

[david s]

Re: Need advise on what chimney/flu combination will draw best?

Dean,
You haven't mentioned how big your oven is. Obviously the larger the oven the smaller the vent can be. The only purpose the vent has is to remove the smoke away from you. Most folk tend to put too much fuel in their ovens and this creates a reducing atmosphere which results in smoke. It is like running a motor on too rich a fuel mixture, inefficient. If the fuel mixture is right there should be virtually no smoke going up the flue. Flames going up into your vent is another indication of excess fuel. In practice this ideal fuel amount is difficult to achieve. My flue diameter is 125mm (5") but my oven is only 540mm (21") diam. It is quite adequate.
Dave

[Wheels1974]

Re: Need advise on what chimney/flu combination will draw best?

Dean,
You haven't mentioned how big your oven is. Obviously the larger the oven the smaller the vent can be. The only purpose the vent has is to remove the smoke away from you. Most folk tend to put too much fuel in their ovens and this creates a reducing atmosphere which results in smoke. It is like running a motor on too rich a fuel mixture, inefficient. If the fuel mixture is right there should be virtually no smoke going up the flue. Flames going up into your vent is another indication of excess fuel. In practice this ideal fuel amount is difficult to achieve. My flue diameter is 125mm (5") but my oven is only 540mm (21") diam. It is quite adequate.
Dave

David,
Thanks for your advice. My WFO cooking circumference is 978mm (38.5") The inside height of the dome is 495mm (19.5") The door of my WFO is 483mm (19") wide and 317mm
(12.5") high.

I have now made the vent a extra 75mm (3") wide. It is now 380mm (15") wide by 115mm (4.5") deep. I'm going to put a 200mm (8") Stainless flu attached to my stainless fabricated void.

You mentioned "Obviously the larger the oven the smaller the vent can be."
is this true? Or did you mean, the larger the oven the bigger the vent?

Regards
Dean

[dusty]

Re: Need advise on what chimney/flu combination will draw best?

I have now made the vent a extra 75mm (3") wide. It is now 380mm (15") wide by 115mm (4.5") deep. I'm going to put a 200mm (8") Stainless flu attached to my stainless fabricated void.

That sounds more than adequate to me and I'm sure it will draw just fine. My vent opening is a bit wider but once the chimney heats up and it starts drawing, I don't think it matters. It sucks like a vacuum.

Congradulations, by the way. Your oven and finished arch look awesome. You'll be swappin' recipes in no time.

dusty

[david s]

Re: Need advise on what chimney/flu combination will draw best?

Dean,
Sorry. My error, yes I meant the larger the oven the bigger the vent. Your dimensions sound about right. Sure you'll be good to go.
Dave