Does a clay flue need to be surrounded?

[phippsj]

I have built a clay flue, recesses at a 45 degree angle towards the center of the oven. I built some small fires today and it seems to draw really well.

The question now is if I need to enclose the clay flue with a firebrick chimney? I am going to build an entire enclosure similar to the second picture below. Is the clay flue OK just sitting in there with the insulation, or should I build a chimney enclosure around it all?

The 'bricks' you see sitting in front of the flue right now are not structural. I just put some thin cuts there temporarily with some wedges to show where I would start building the chimney up. A 45 degree inclined chimney will not be much fun, but I think I can do it!

Thanks!
-jared

[phippsj]

Sorry... here is the photo of the example oven.

[phippsj]

OK, nevermind, I answered my own question... I missed this line in the instructions "The separation of the flue liner from the surrounding concrete or masonry shall not exceed the wall thickness of the flue liner". So I will have to surround it with masonry, and my oven enclosure can't be considered that masonry surround

[dmun]

Well, yes, your oven enclosure, if solid masonry like the one pictured, can substitute for the masonry chimney. After all, every masonry fireplace has a broad taper leading up to the chimney where the stack of flue tiles is unsupported.

In earthquake zones, that airspace is substituted for refractory insulation to keep the flue stack from moving around when the earth moves. Since you need to support a semi-horizontal run of tile anyway, you may want to consider packing vermiculite concrete around the flue where it's in the larger enclosure.

[phippsj]

Originally Posted by dmun

Well, yes, your oven enclosure, if solid masonry like the one pictured, can substitute for the masonry chimney. After all, every masonry fireplace has a broad taper leading up to the chimney where the stack of flue tiles is unsupported.

In earthquake zones, that airspace is substituted for refractory insulation to keep the flue stack from moving around when the earth moves. Since you need to support a semi-horizontal run of tile anyway, you may want to consider packing vermiculite concrete around the flue where it's in the larger enclosure.

Interesting. I was planning on using steel frame and cement board, and then running stone and brick all the way up (including the ceilings). In that case if I put in the portland cement/vermiculite mixture versus loose fill, and let that mixture cover the flue, then I would be OK? Or even better, just the portland/vermiculite around the flue and loose fill everything else? That won't be too tight on the clay tile? If that is the case then you just made my day! Thanks for all your feedback by the way, it has really helped through this build process.