Single or Double walled Stainless?

[MeBeMarc3]

Should I buy single wall (uninsulated) or double wall (insulated) stainless for my flue? How tall should I go with an 8" flue? it's a 36" oven. Thanks in advance for taking the time to discuss.
Marc

[deejayoh]

Double wall for sure. 8" is probably overkill for a 36" oven. I think the FB 36" ovens use 6" (check me on this) - but you only need to go high enough to have adequate clearance beyond whatever you are using for roofing

[david s]

If you are planning on having a brick chimney as in the pic, you shouldn't even need a single stainless flue. Really the only reason a double is called for is if you are penetrating a roof or if you are particularly concerned about someone burning themselves leaning against the flue. This is hardly a concern as it's well out of the way.
A 6" diam flue is sufficient for a 36" oven, but you can't over flue this design.

[MeBeMarc3]

Double wall for sure. 8" is probably overkill for a 36" oven. I think the FB 36" ovens use 6" (check me on this) - but you only need to go high enough to have adequate clearance beyond whatever you are using for roofing

Thank you for the response! I don't plan on putting a roof over it and It will be a clay brick chimney surrounding it. Would this change your recommendations?

[MeBeMarc3]

If you are planning on having a brick chimney as in the pic, you shouldn't even need a single stainless flue. Really the only reason a double is called for is if you are penetrating a roof or if you are particularly concerned about someone burning themselves leaning against the flue. This is hardly a concern as it's well out of the way.
A 6" diam flue is sufficient for a 36" oven, but you can't over flue this design.

So are you suggesting no flue? The chimney itself will be sufficient? I have planned to over-flue from the get go, since I've heard people say that they were having venting issues and they wish that they went bigger.
Thank you,
Marc

[deejayoh]

Actually, I wasn't remembering your design. With a brick chimney, then you don't really need to double wall. Single wall is fine because as davids says, nothing to catch fire. But I would line the chimney - just to keep the smoke away from the mortar. Who knows how it may break it down over time. I bet you could get away with a clay flue liner like they use in most fireplaces.
If you can get 8x8" flue liners (super cheap) that is plenty big for your oven. As to height - the shorter the height, the bigger diameter flue you need. It's all about velocity. A 6"flue is great with a four foot height, probably not as good at 2 feet.

[mefornaio]

As David pointed out none is necessary. With an outdoor brick chimney there is no reason to put a flue liner.
As you lay the chimney courses go back and line them with a layer of fire clay mortar enough to smooth everything out, every foot or so as you work your way up. Let that set up just a bit and go back in with a good damp sponge and smooth the mortar out. This should be more than sufficient. As far as my experience goes soot doesn't kill chimneys heat, voids and moisture do.
You can do a heaver cement ratio for this mortar than for the dome as it will not see as much heat. This is the way old school chimneys were built for decades prior to clay liners and modern steel liners.

[MeBeMarc3]

Thank you all! I am kind of anxious about this decision. I want to have a good draft, longevity and try to keep moisture from entering the oven through the top. Should I use a damper to keep out moisture? Are rain and snow going to enter the chimney. If they do, they will drip onto the oven floor, which is not water tight and it sets on a layer of rigid insulation that will soak it up like a sponge.

[MeBeMarc3]

This is my design so far. Any suggestions on how the top should go?
Thanks,
Marc

[mefornaio]

First of all your oven looks great.
I noticed that your in Maine, I grew up in PA but have been in CA for many years now so I have not had to deal with freeze thaw cycles in a long time.
I think your over thinking things a bit. (I have a degree in that lol) look around you at the chimneys on homes in your area they probably have a spark arrestor cap or a weather cap of some sort or maybe none at all. The chimney you are building serves the exact same purpose and functions the same as for a home its just smaller. You could make or have someone make a nice metal old world looking weather cap. OR....

What i think would go really nice with your design is to make a modified brick version of this cap. Pic is just to illustrate the concept not design,




Solider position

Make a solider course of full or half or 3/4 bricks whichever you think look good in scale of oven, at the top following the curve of the chimney staying just slightly inside the edge (not to have bricks over hang edge of last course).

From the looks of you chimney or proposed chimney design if you place each solider on the corresponding last course you should work out even and have gaps where your joins are. Or lay it out dry to get all full bricks and not have a weird cut while achieving a uniform gap.

Then cap it (like in the pic) with a piece of the stone you are using for the oven. If you are still worried about water/snow a nice waterproof canvas cover over the top with a draw string would keep everything out when not in use and easily removed.

[Gulf]

I intended to install a proper masonry cap. But, I had wanted to leave myself an option in case that I needed to extend the flue height. Long story/short version, I installed an 8" pipe flue cap. Painted it with black stove paint so that it wouldn't stand out too much....................Then Gaudied it up a little so that it would . The oven doesn't smoke, I don't need to extend the flue, and, I probably wont ever get around to building a proper cap . This link back to my build has little more on it. Flue Cap

[MeBeMarc3]

First of all your oven looks great.
I noticed that your in Maine, I grew up in PA but have been in CA for many years now so I have not had to deal with freeze thaw cycles in a long time.
I think your over thinking things a bit. (I have a degree in that lol) look around you at the chimneys on homes in your area they probably have a spark arrestor cap or a weather cap of some sort or maybe none at all. The chimney you are building serves the exact same purpose and functions the same as for a home its just smaller. You could make or have someone make a nice metal old world looking weather cap. OR....

What i think would go really nice with your design is to make a modified brick version of this cap. Pic is just to illustrate the concept not design,




Solider position

Make a solider course of full or half or 3/4 bricks whichever you think look good in scale of oven, at the top following the curve of the chimney staying just slightly inside the edge (not to have bricks over hang edge of last course).

From the looks of you chimney or proposed chimney design if you place each solider on the corresponding last course you should work out even and have gaps where your joins are. Or lay it out dry to get all full bricks and not have a weird cut while achieving a uniform gap.

Then cap it (like in the pic) with a piece of the stone you are using for the oven. If you are still worried about water/snow a nice waterproof canvas cover over the top with a draw string would keep everything out when not in use and easily removed.

Wow! Thank you for the input and photos! It was nice to know that I was over thinking things. I saved some time and money and simplified things. I intend to use granite to finish. Thanks again!

[MeBeMarc3]

I intended to install a proper masonry cap. But, I had wanted to leave myself an option in case that I needed to extend the flue height. Long story/short version, I installed an 8" pipe flue cap. Painted it with black stove paint so that it wouldn't stand out too much....................Then Gaudied it up a little so that it would . The oven doesn't smoke, I don't need to extend the flue, and, I probably wont ever get around to building a proper cap . This link back to my build has little more on it. Flue Cap

Love the crown! Putting your own twist on things customizes them. Now its one of a kind and your build stands out among the rest! I am leaving a short chimney and hoping that it won't need to be longer. I think I'd have to go 7 rows higher to complete the twist. I'll be curing the oven asap.
Thanks again for your help and encouragement.

[Gulf]

I'm looking forward to "the twist". I have always thought they were cool!

[MeBeMarc3]

Thanks all! I took some time off from pizza oven construction and got busy with other stuff.
So I've cured the oven and have one successful pizza night under my belt!!!! Looking to make some bread, with residual heat, next time I fire this thing up.
One issue... the oven drafts well.... until there is a breeze. Then the breeze will pull some smoke out of the front. Not much, but still, some smoke escapes. Could it be wind pushing down the top of the chimney? Therefore should I get a different cap? I do have a large stone, temporarily suspended 8" above the top, resting on 4 full bricks.
Or would extending my chimney help with draft? If neither option is going to make a difference I can always live with what I have. It's really minimal and only during a cross breeze.