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dottavio 08-10-2012 05:54 AM

Gap Between Vent and Dome
I finally finished my dome and I am ready to start my vent. I have been doing some research and noticed that some builders leave a gap between the dome and the vent. The idea, as I understand it, is to create a thermal break between the two.

Not sure if that thought is valid or if leaving a gap will compromise the structural integrity of the chimney, which in my case will be a Duravent with an anchor plate.

Once again I turn to the Forno Bravo forum for your thoughts and feedback.

Fire away......pun intended :)

david s 08-10-2012 02:07 PM

Re: Gap Between Vent and Dome
If you insulate between the the entry and the dome then you are essentially building two separate structures. In my opinion it is better to insulate the entry from the outer arch so the whole inner dome and entry are one and free to move while the outer decorative arch is tied to the outer shell.A compromise is to use some insulating firebrick between the entry and the dome, but these lack strength and won't provide a thermal expansion joint.

Faz 08-11-2012 12:26 AM

Re: Gap Between Vent and Dome

On my build the complete entry arch is separated from the dome. There is a half inch gap between the brickwork. I worked some of the external vermicrete into this gap but most of it is an air gap. There is also a layer of vermicrete between the dome floor and the floor of the entry. The first pic below shows the vermicrete thermal break (it is the rough textured material which sits just outside the dome arch). I have tiled over this break so it nice and smooth and cannot be seen on the completed oven (see the second picture).

dottavio 08-11-2012 03:16 AM

Re: Gap Between Vent and Dome

Thanks for the pics.

I sometimes get hung up on the science of this whole project. Looking at what you did there is not a "true" thermal break as the heat can conduct through insulating concrete and the tiles, but then again your design must stop some heat flow

How much cooler is your vent compared to the dome?

Also, to David's point, since you now have two seperate structures did you have any stability issues with your chimney? I was looking to install a 4' length of Duravent pipe and am concerned that the vent not being connected will not give its base enough stability.

Then again, perhaps this is all over thinking on my part as usual....

Doug O

Faz 08-12-2012 01:33 AM

Re: Gap Between Vent and Dome
Yes there will be some heat conducted through the tiles, but as that layer is only approx 15mm thick in total the amount of heat lost through this route is greatly reduced.

I haven't measured the actual temperatures on the floor, but there is a noticable difference when placing my hand across that break area.

david s 08-12-2012 03:22 AM

Re: Gap Between Vent and Dome
I'd imagine that you should be able to hold your hand against the entry even when the oven is SERIOUSLY HOT. Thus you keep the heat only where you want it. I like your solultion with the tiles overlapping the vermicrete.

dottavio 08-12-2012 09:51 AM

Re: Gap Between Vent and Dome
I am cutting my vent bricks as I am typing this, lunch break...

Very interesting Kaz. You've definitely given me some food for thought. I suspect I could even rip the fire bricks to 1/2" and accomplish the same thing as the tile. My floor is inside my oven so I can rework if necessary.


Doug O

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