Oven Landing Measurement Help

[Brick Oven Nick]

I'm building a 40" Pompeii Style oven. I am ready to place my insulation board on my hearth with the firebrick oven floor to follow. I want to make sure that I place the floor onto my hearth in the correct position. I am struggling with the length measurement on the oven landing / vent area. Does anyone have any measurement suggestions?

I have planned for a 20" wide opening. So where the opening meets the radius of the circle I am assuming a 4.5" brick there to create the first arch. Then a small thermal break, then a 9" full brick to create the front arch. In the middle of this arch the brick will be trimmed down to 4" to create a 5" opening for the vent. Then in front of this arch, I will have a decorative brick arch of 3.5". Lastly I want to leave 2" from front edge of my hearth.

So if I was measuring the depth of this area from the front edge of my heart it would be, 19" to the inner arch inside, or 36" to the center of my oven. 2" +3.5"+4"+5"+4.5"=19". Does this sound correct? It seems too deep to me. My vent opening area will be 5" x 17". I will eventually set an 8x8x24 clay flue as the vent upward.

Photo attached showing my layout. Thanks for any advice here.

[SableSprings]

Many of us have faced this "length" issue. Remember that your arch bricks are going to be supporting the vent/chimney opening, so they won't be contributing their full dimensions to the landing depth. So your 4.5" arch bricks are part of the dome...not necessarily an additional arch. I also used 8x8x24 clay flue vent, but didn't realize the sides of that clay flue are 1" thick...which means you will only have a basically a 6" diameter chimney. I wish I would have used the next size up, as I do get more smoke escaping out the front than I'd like. I suggest that you use 12x12 diameter flue pipe for your 40" diameter oven (10x10 wasn't available in my area last time I looked ). Following this, I'd suggest your planned 5" x 17" smoke collection area be enlarged to match the flue pipe more closely. In other words, make the collection area 8" or 9" deep. When the firing flame/heat/smoke is emerging out the top of the oven opening, they arch out and up. With only a 5" opening, that exhaust will be hitting the second arch a little more directly than I'd like (obviously this is my opinion...but give it some thought). I really do think the larger diameter flue pipe here will help your oven's proper (and directed) breathing.

Although my 39" dome's opening is the old angle iron square top, some of my build pics may help you see what I mean about the arch bricks in relation to the total landing depth. Look at the pictures in posts #14 through #16 of the opening/vent area in my thread (link below)

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/386552-the-dragonfly-den-in-retrospect-june-2009-may-2012

The bull nose bricks in front of my ash slot are approx. 9" long. Also, not sure with your sketch, but I'm assuming you are not extending insulation board beyond your heat break...no need or advantage in doing so.

Hope this helps a bit...looking forward to your progress.