Chimney Size and Design

[UtahBeehiver]

What is the ID of the oven and the ID of the chimney?

[Solaris1965]

Hi there Icripe.I've just been reading your post about extending the height of your chimney, nice build! I too have too much smoke coming out the front and have remade the flue to give a big box entry, rather than a simple hole going into the chimney.If you could clarify something I'd be really grateful.

To get your chimney to draw better, was it just a case of extending the height, or did you do anything else? My chimney is quite short and I was thinking a higher one may help.

Here's a pic

https://photos.app.goo.gl/sVS4gFdR6rChT9Jk6

Many thanks
Dave

[lcripe]

Re: Chimney Size and Design

Does any have thoughts on placing the chimney on the BACK BOTTOM of the oven?
Wouldn't this vent the cooler air to maintain more heat in the oven??
Eli Rogosa

Yes. Don't!

I think if you check postings here in the forum and do some study you will find that it won't work. Go with the tried and proven.

[Tscarborough]

Re: Chimney Size and Design

10% of the door opening. If your door is 18x18 (324 SqIn), for example, then your flue should be 32.4 SqIn, i.e. 6x6 ID. Fudge on the side of over sized, and realize that that calculation is technically for round flues.

[sonomacast]

Re: Chimney Size and Design

The rule of thumb when building an open fireplace is, flue size should be 10% or more than opening size

I don't understand this, The flu should be 10% or more than what? thanks

[lwood]

Re: Chimney Size and Design

MOFO, what is the diameter of your chimney?

[BackyardPermaculture]

Re: Chimney Size and Design

DJ,
It can also be the wood you are burning. I used some (untreated) softwood offcuts that smoked like crazy, even in a top-down fire. Despite my 6" (6' tall) flue drawing very well, that smoke came pouring out the front. As the oven has dried right up and I'm using decent hardwood and stacking a good top-lit fire, almost no smoke comes out the front.
Cheers,
Mick

[david s]

Re: Chimney Size and Design

DJ,
Post some pics. It might not be just the flue size. Is your door height correct relative to the interioe height? You also need some volume below the flue pipe so the smoke funnels up. Also if your oven is new it will smoke a fair bit because it is still moist and does not fire efficiently. If this is so then maybe you just need to fire it lots and your problem may disappear.
Dave

[canadianmofo]

Re: Chimney Size and Design

Hi. New here. Love the site!

I have a design flaw and am trying to resolve a smoke issue (comes out the front).

I have a rectangle burning/cooking surface approx. 100cm x 70cm. The chimney is obviously too small. Any suggestions on chimney size? From what I'm reading, I'm guessing either 6" or 8" would be sufficient. I need to cut my way in to expand the size.

thanks.
- dj

[david s]

Re: Chimney Size and Design

That is a really good idea, but you will need around 2% by weight. Thatis a lot of staples. Hope you've got a good office budget.

[fxpose]

Re: Chimney Size and Design

Stainless needles are the reinforcement of choice.

I can't seem to find stainless needles locally.....but I have plenty of stainless steel staples for the standard office stapler. Perhaps I can unload a few hundred of those instead.

George

[fxpose]

Re: Chimney Size and Design

Thanks David, that's exactly what I imagined could happen. I will give it some wiggle room for expansion.

George

[david s]

Re: Chimney Size and Design

George,
If you cast directly against the flue pipe it will get hot first and expand and perhaps cause the castable to crack. This happened to the second oven I built. You can wrap some cardboard around the pipe when you cast it, remove the cardboard and pipe, then reinsert the pipe and fill around it with vermicrete. It is better for the flue to bea slightly loose fit to reduce stress on your casting.

[fxpose]

Re: Chimney Size and Design

I don't think rebar is used in refractory castable. Stainless needles are the reinforcement of choice.

I kinda figured that as I have not seen rebars used in any of the cast oven builds.
Are stainless needles commonly available? I've seen them on Ebay before.

George

[dmun]

Re: Chimney Size and Design

I don't think rebar is used in refractory castable. Stainless needles are the reinforcement of choice.