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Old 06-25-2012, 10:37 AM
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Question Stuck at chimney. Need pictures and instruction.

Hello fellows. I'm stuck. I can't make heads or tails of the FB plans where it concerns the chimney. My oven is 46". I'm having the worse time finding specs on what size my chimney must be. I think 8 x 10 inches? What if it is bigger?

Can it be built entirely of brick? Must it be lined with a flue? I'm not grasping the science behind the draw and search results are not getting me any closer to answers.

Can I build the arch entry, set a nice level footer/base up there for a clay flue liner, mortar it in place and call it a day? Addition of a chimney cap of some sort added in there.

Can a terracotta flue liner act as the chimney - or does it have to be lined - will it take the heat? I would prefer it be exposed vs insulating it, can I do that? (I'm going for an igloo shape, not an enclosure and I love the looks of the terracotta.)

I can't find definitive answers or pictures to guide (I love pictures!) my next steps. Can any of you point me to some good posts on these topics?

I would rather build another dome than have to try to tackle this chimney! I just can't see it in my head.
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Old 06-25-2012, 11:57 AM
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Default Re: Stuck at chimney. Need pictures and instruction.

Here was my approach. Refer to post #134. If you dig a little deeper, you can see that I added another section on top (after I tapered it). To get the base to fit I used an angle grinder to form the arch - wasn't too bad to do.

http://www.fornobravo.com/forum/8/le...d-4207-16.html (Les' Build)
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Old 06-25-2012, 06:18 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

http://www.fornobravo.com/forum/f9/v...ner-17012.html (Vent transition for clay flue liner)

That's my solution to the vent and transition, with pictures shoeing the brick cuts. You need 8 inch INTERIOR diameter clay flue liner, which means you'll probably have to ask for 10 inch liner at a masonry supply house.

You want to line the chimney because unless you're building it from fire brick, the thermal cycling will break down your material over time. Even if you line it, you still want an air gap between the liner and facade brick.

Also, clay is a lot easier to clean than brick. All sorts of gunk will build up in the chimney over time, and you will have to get a sweep to clean it.

Clay liner can certainly take the heat, but it is liner rather than a material intended to be exposed. Terra cotta will wear down when exposed to the elements and repeated wet/dry hot/cold cycles. But it's cheap and if you're wiling to repair it when needed, then have at it!

The chimney's draft is a function of its cross-section and height. I won't get into the math, but the wider the chimney, the more it draws. Also, the taller the chimney, the more it draws. However, a change in the cross-section causes a greater change in draw than does a change in the height. Bottom line is: a wider chimney can be shorter, while a narrower chimney must be taller to move the same amount of air. For example, if you have a six inch flue, your chimney needs to be six feet tall yo draw as much air as a three foot chmney with an eight inch diameter.

Last edited by azatty; 06-25-2012 at 06:26 PM.
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Old 06-25-2012, 09:09 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

Thanks fellas! I'll look these over carefully. I'm not terribly confident in my masonry skills, so I was worried about supporting the weight, @azatty, your pictures and description are very helpful. The explanation of the draw is very helpful too.

I actually have a rather short section (maybe 15-inches?) of 10-inch interior clay flue that was just remove from our chimney that we had closed up, I had wanted to use it, but it seemed too heavy. If I could get away with a shorter chimney and use it, that is kind of appealing. I really like the shorter chimney.

@Les, how tall is your chimney and what size flue do you have? It also looks like you have vermicrete or something between the brick and the flue, would that be right?

I have the figure of 3-inches above the dome in my head for some reason, if I have a 10-inch flue, does it sound reasonable that I could get away with having a chimney that is only about 3 inches taller than my dome? I could be making up that number, but seems like I read it somewhere the past few days.

Thanks again, I surely appreciate your opinions and guidance!
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Old 06-25-2012, 09:47 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

Quote:
Originally Posted by Xene View Post

@Les, how tall is your chimney and what size flue do you have? It also looks like you have vermicrete or something between the brick and the flue, would that be right?
Xene,

I used 2 pieces so it is 24 inches tall. If I recall the size is approx. 8 x 14 od. Yes, I did put vermiculite between the flue and finish brick. I used standard type s mortar on the finish so apparently it worked - zero cracks.
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Old 06-26-2012, 03:50 AM
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Default Re: Stuck at chimney. Need pictures and instruction.

Xene
Some pics needed. I looked back and saw in another of your threads that you have built what appears to be a semicircular arch to your dome. You could do worse than yake a look at Sharkeys (between a rock and a hard place) flue transition which I copied. It is ideally suited for a rounded arch. Azatty's solution looks fantastic and is very well thought out, but maybe unneccessarily complicated for the rounded entry arch which should be better at load bearing, and shouldn't need buttressing.
This is sharkys flue transition
http://www.fornobravo.com/forum/21/b...tml#post110964 (Building Between a Rock and a Hard Place)

To execute this the arch bricks should be tapered. As you go up (about the 4th brick) you cut them in half (or whatever) and continue the arch with the outer half and flip over those going up the vent.
The pic is my copy. My entry is probably a bit narrow to handle a flue of the size you are talking about but it gives an idea of how it works out.
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Old 06-26-2012, 10:43 AM
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Default Re: Stuck at chimney. Need pictures and instruction.

A round arch will definitely bear the load without the buttressing; you can build straight onto it. I stole the general shape of the scissor bricks from a round arch build, except in the round arch the bricks were oriented more or less straight up to an anchor plate. The notches at the bottom of the brick appeared to tie the transition to the arch better than just plain mortar.
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Old 06-26-2012, 08:45 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

All of this has helped a LOT! I think your pictures and advice will be just what I need to get it together, I'm seeing it now! I'll post a bit as I go, hopefully if it looks really off someone will tell me. Thanks all!
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Old 06-29-2012, 02:16 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

I've been busy on the entry, my blade went dull on me for the last cut I needed, so I don't have the front support for the chimney in place, but I was able to get the back cut, those will act as the platform for the clay flue. (Parallel to the level in the pictures below.) I will cut 2 more for the front, those are thin though, 1 1/2 wide - but the front still gets a facing of red brick, so once it is mortared all together, I think that will add the structure I need to make it more solid. Then add a wide section to fill in those side and mortar the clay flue to that platform.

What do you think? Have I done a sturdy job of it? Maybe I should add another layer of bricks laid opposite the first set of mortar joints to make it more solid?
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Old 06-29-2012, 06:22 PM
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Default Re: Stuck at chimney. Need pictures and instruction.

Augh, I've made the draw opposite what it should be haven't I? I'm really making a good impression. I'm not a space cadet - I just don't have my heart in it like I should.
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