a few vent/flue qestions

[jimkramer]

Not sure yet if I’m going with an insulated metal flue or clay, sp..

-If I use a clay flue, how do I secure it to the vent? Directly with mortar? Or do I use an anchor plate, same as a metal flue?

-Is a 12” deep vent enough room for both an 8” interior duravent and also for a clay flue?

-If I go with clay, can I put a spark arrester directly on it? If yes, do they have them for all shapes? (I’d like to go round for the look of it if I go with clay.)

-Is a 2ft high flue sufficient?

[SableSprings]

Re: a few vent/flue qestions

I used clay flue pipe for my 39" (internal diameter) oven. I saw a post on this forum where two rectangle pipes were cut at an angle and then joined with refractory mortar (sorry, I don't remember the thread...). The concept was to make a larger, collection area at the base that funneled the heat and smoke up. So after joining the two pieces, I set them on top of the gap I'd done at my chimney arches with a little mortar. I actually nested two flue pipes for the rest of the chimney to give myself a little insulation and protection of the "free standing" main flue. Note that I built a facade of brick around the clay flue pipe that only extended up just above the roof sheeting. I did find a chimney cap with a spark arresting screen that can be tightened directly to the outside flue section.

I attached a few photos that might help show you what I did. I went up quite a bit further with the brick facade when I put an enclosure around the oven, but I still used the original cap and attached it directly to the top clay flue tile. The last two shots are 1) when I extended up another section to help increase the draft a bit and it shows the nested flue pipe sections with a little of the brick tops from the lower enclosure showing at the base and 2) the chimney flue and cap above the Dragonfly Den as I see them from my kitchen window.

Check with the local fire department about chimney heights...most of the building codes in the US specify distance to nearest combustible and a minimum height to make sure downdrafts are not an issue. If you don't have a structure really close or don't have the chimney rising up through a "building" then you're mostly concerned about having the chimney high enough to keep startup smoke and ash from blowing on you or your guests.

[GianniFocaccia]

Re: a few vent/flue qestions

Jim,

Here's the link to Saginaw Mike's excellent build that SableSprings is referring to. Several builders here have spliced flue tiles with elegant results. The biggest concern of any clay flue is cracking, which can be reduced by insulating, and gradual firing. They are mortared directly to the top of your vent.

http://www.fornobravo.com/forum/21/m...o-4832-17.html

12" is a little tight for an 8" flue, but it can be done. Superior Clay flue tiles are carried just about everywhere. Check out their catalog, which may include a 7" flue(?) They also carry really nice chimney pots.

http://www.ewgroupinc.com/docs/Super...ay-Catalog.pdf

John

[jimkramer]

Re: a few vent/flue qestions

Thanks John. So how deep would you say the vent needs to be for an 8" flue?

[GianniFocaccia]

Re: a few vent/flue qestions

Ideally, one would construct an entryway with two 4"-thick arches between which the 8" flue can rest. I seem to recall Superior Clay producing a 7" x 12 (or 13) flue, which would work well, I think.

Scan through a number of builds and you'll be amazed at how many different ways there are to skin a cat.

John

[jimkramer]

Re: a few vent/flue qestions

So one last vent question, I think. I have a remnant piece of marble and one of granite. Could I use either for the floor of the vent, or will they crack from heat? I'll have a 1/2" heat break in front of the oven made with ceramic rope running through a piece of ss channel.

[Tscarborough]

Re: a few vent/flue qestions

Granite would be better than marble, but both should be OK.

[GianniFocaccia]

Re: a few vent/flue qestions

During normal firing, cool air is drawn across the entryway floor into the oven. After the fire subsides, residual heat emanates outward from the oven. Along with a door, it is at this point that a heatbreak proves its worth.

[jimkramer]

Re: a few vent/flue qestions

Glad again I'm doing the heat break! Can I use my brick saw to cut the marble or granite? Also, I'll have to raise it 3/16" to be flush with the oven floor. Can I use a piece of ply to raise it up? I could put it under a board of insulation. Or will it decompose too quickly?

[GianniFocaccia]

Re: a few vent/flue qestions

With a heatbreak in place, you can support your entryway floor with insulation, firebrick, concrete, whatever. Your choice. Do not use wood of any kind. My stainless entryway floor sits on 2.5" of firebrick that is supported by 5.5" of CF board and vermicrete.

Just make sure you slope the entryway floor away from the mouth of the oven a few degrees for drainage.

[jimkramer]

Re: a few vent/flue qestions

Well, I decided to nix the granite, go with brick. The wife said she likes the herringbone pattern more.

I'm still obsessing about the depth of the vent. Functionally (as in, placing trays/peels/etc) on the vent floor, how much room do you all find you need?

Also, I got the 8"/24" clay flue, but it's a heavy mutha. Think I can get away instead with 7"inner diameter/12" high? I'm concerned about so much weight on the arch.