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-   -   Chimney, Leading heat away from WFO??? (http://www.fornobravo.com/forum/f2/chimney-leading-heat-away-wfo-20255.html)

Madsen 12-27-2013 02:23 AM

Chimney, Leading heat away from WFO???
 
Gdday guys,

I'm quite new in this world - actually a big newb, I just signed into this forum today :) - But i had the ideas for this WFO for some time now.

My plan is to make an WFO beg 14' so now i'm prepping my self on the design, and the does and dont. Its going to be a 42" Pompeii (for now atleast)

I have a questions in regards to the chimney for a WFO - the title is more or less self explanatory, but the idea of a chimney is to lead the smoke away from the Master Chef cooking, right ? But as heat rises up towards the roof. Dosent this lead all the heat out of the dome ? Or do a chimney based WFO need some kind of dampers to prevent this heat loss ? - I tried to google and use this forum, but no luck - maybe its the danish words translated into English thats wrong.

Madsen...

PS. The wording and the spelling mistakes are 100% free - i'm from Denmark :)

Les 12-27-2013 09:02 AM

Re: Chimney, Leading heat away from WFO???
 
Madsen.

Our designs have the chimney / vent on the outside of the dome. Download the free plans from the store, it will give you a better idea on how all this goes together.

Madsen 12-27-2013 10:07 AM

Re: Chimney, Leading heat away from WFO???
 
Hi Les,

Thanks for the input, I have received the PDF and it's also clear to me now.

Thank you.

brickie in oz 12-27-2013 12:34 PM

Re: Chimney, Leading heat away from WFO???
 
If you want a flue inside the oven then yes, you will need a chimney damper. :)

SableSprings 12-27-2013 01:33 PM

Re: Chimney, Leading heat away from WFO???
 
Quote:

Originally Posted by Madsen (Post 167369)
I have a questions in regards to the chimney for a WFO - the title is more or less self explanatory, but the idea of a chimney is to lead the smoke away from the Master Chef cooking, right ? But as heat rises up towards the roof. Dosent this lead all the heat out of the dome ? Or do a chimney based WFO need some kind of dampers to prevent this heat loss ? - I tried to google and use this forum, but no luck - maybe its the danish words translated into English thats wrong.

Madsen...

As Les noted previously, the free Forno Bravo plans are really helpful in understanding how these ovens work. Yes, the chimney takes smoke and heat away from the oven and the cook...but the fire in the chamber heats the bricks (where some of that heat is stored), adding a lot of radiant and reflective heat to the chamber. For pizza, you need to have a 1-2 hour fire in the oven to bring it up to cooking temps. (Think of this as using a wood stove in the house. Yes, you lose heat out the chimney, but once warmed up, the stove radiates heat into the house.) After the hearth bricks are hot enough to properly cook a pizza skin, you need to continue having a fire off to the side to cook the pizza on top (with reflective & radiant heat).

The chimney in Forno Bravo plans is set in front of the firing chamber. When you start an oven fire, air flows in from the front opening (lower portion) to the fire inside. As the fire burns, heat/smoke move up and back. Then the fire exhaust gases move forward along the curved top, circling back to the opening. The heated gases warm the bricks on their way and exit up and out the chimney via the top portion of the front opening. When you start a fire, you see a clear division of cool air entering below and smoky warm air exiting above when looking at the oven opening. (It's really fascinating to watch an oven breathe in this manner!)

Hope that helps a little, but the plans explain this much better. You only need a damper for the chimney if you place the chimney inside the firing chamber. With the chimney outside the oven chamber, you can remove the fire/coals, close the chamber with an insulated door, and keep baking temps inside the oven for a pretty long time!

Madsen 12-27-2013 02:40 PM

Re: Chimney, Leading heat away from WFO???
 
Alright SableSpring, i took notice, and i have in the last couple of hours read the pdf on some 70 pages. Quite good reading! and I also learned about the door position, before i thought the door would be placed on the outside of the chimney vent, so all the hot air would travel up and "heat the garden"

But now i'm even more excited, damn new-years-eve-time - all shops are closed until 02.01.14 :D

Madsen..

wotavidone 12-27-2013 06:01 PM

Re: Chimney, Leading heat away from WFO???
 
Build it like the plans and you will be astounded at the efficiency. The hot gases from the fire contact a lot of brick in a very efficient manner before they exit the dome and turn up into the chimney.
I have sometimes wondered if any clever engineer has made any sort of calculation or measurement as to how much heat (perhaps in terms of a percentage of the heat available from the burning fuel) is transferred to the bricks compared with say an open fire place?

stonecutter 12-28-2013 03:56 AM

Re: Chimney, Leading heat away from WFO???
 
Quote:

Originally Posted by wotavidone (Post 167400)
Build it like the plans and you will be astounded at the efficiency. The hot gases from the fire contact a lot of brick in a very efficient manner before they exit the dome and turn up into the chimney.
I have sometimes wondered if any clever engineer has made any sort of calculation or measurement as to how much heat (perhaps in terms of a percentage of the heat available from the burning fuel) is transferred to the bricks compared with say an open fire place?

There are way too many variables to get any reliable numbers for some sort of chart.

Lburou 12-28-2013 10:40 AM

Re: Chimney, Leading heat away from WFO???
 
Madsen,
Welcome. Your spelling is good.
As you read the plans, the design will come into focus. Keep digging for that information. :)

wotavidone 12-28-2013 01:08 PM

Re: Chimney, Leading heat away from WFO???
 
Quote:

Originally Posted by stonecutter (Post 167423)
There are way too many variables to get any reliable numbers for some sort of chart.

I guess, but I assume you would agree the Pompeii style oven does appear to be way more efficient at capturing heat from the fuel than an open fire?.


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