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Old 09-02-2009, 08:37 AM
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Default Vent to Flue Transition Question

Hello Forum Members,

Any thoughts on how much tapering with brick is needed between the rectangle of the vent and the round opening into the chimney? Can I just go from box to to pipe or do I need to create a funnel shape in mortar of metal?

Also, do I need to insulate the arch or can I just insulate the dome?

Thanks
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Old 09-02-2009, 09:26 AM
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Default Re: Vent to Flue Transition Question

You'll get better draw on start up with a tapered transition between mouth and flue. A taller flue will help a lot too. If you don't mind a little smoke staining on the front of your oven, you can probably get by without either.

Insulation around the arch helps keep heat in the dome, that area gets really hot and insulation reduces the amount of heat-leakage.
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Old 09-02-2009, 11:30 AM
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Default Re: Vent to Flue Transition Question

I don't mean to redirect this thread, but following up on your comment dmun, are you suggesting 4" insulating concrete (or a blanket) over the entry arch? I don't think I've seen that in many of the photos.
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Old 09-02-2009, 11:49 AM
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Default Re: Vent to Flue Transition Question

I insulated my archway and my flue tile funnel, which in my case was very close to the dome. Partly this was because it was in an enclosure that I was dumping vermiculite concrete into anyway.

Another factor was that I was building a reinforced concrete bridge to support my two story chimney, and I wanted something non-combustible to pour the slab onto.
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Old 09-02-2009, 02:06 PM
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Default Re: Vent to Flue Transition Question

Thanks for the insights. I am doing an igloo of stucco over the dome after I attach the 3 layer blanket of insulation.
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Old 09-02-2009, 02:17 PM
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Default Re: Vent to Flue Transition Question

I am hoping to do an igloo/stucco design myself (undecided on blanket vs. perlite cement insulation). I will be watching you closely. Please post photos and gathered wisdom!
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Old 09-09-2009, 06:30 AM
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Default Re: Vent to Flue Transition Question

If it helps, here's what I did with my arched entry area and blanket.



It's an inch blanket folded back on its self so I got a nice edge toward the decorative brick arch.
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Old 10-01-2009, 10:53 AM
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Default Re: Vent to Flue Transition Question

Quote:
Originally Posted by timo View Post
If it helps, here's what I did with my arched entry area and blanket.



It's an inch blanket folded back on its self so I got a nice edge toward the decorative brick arch.
Greetings to a fellow Texan:

I am looking at finishing like yours and ask how you keep the stucco render from cracking since it is laying on top of a compressable substrate? I am sure you put chicken wire or stucco lathe to re-enforce the stucco but am not sure what happens strenth wise if the stucco is compressed. (such as when a 9 yr old chucks his baseball against the stucco
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Old 10-01-2009, 11:09 AM
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Default Re: Vent to Flue Transition Question

I fastened chicken wire all around and anchored it. I applied a thick scratch coat, then a thinner coat, then a sponged final coat. I can stand on top of my stucco dome and it is solid. I haven't had the misfortune of having it kid tested, but there is still time and kids playing in the backyard...
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Old 10-01-2009, 11:37 AM
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Default Re: Vent to Flue Transition Question

For myself I used chicken wire over the blanket, it was much easier to fashion/form into a dome like shape than the usual stucco mesh and without all the joyful cuts one gets when working with stucco mesh. I then laid on a thick brown/scratch coat making sure to force the stucco mix underneath the chicken wire and then on top. Also a good suggestion is to sprinkle plastic fibers you get by the bag from the masonry supply folks into the stucco mixture. It has two benefits for the scratch coat, first it adds strength and the little hairs give the next coat something to bond to (it can't hurt).

I don't have pictures to show the steps, rain was forecast the next day I insulated and applied my first coat of stucco so I had to do it all in one day. I wanted the rain the following day to help cure the stucco since the summer here was exceptionally dry.

It's all worked out well. I endorse using blanket insulation. I bought 3 boxes for my oven and it was enough to cover it in four layers. I've had the oven over 950 degrees and the exterior of the dome is still at ambient air temperature.
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