WFO 2021 Build - HELP

[Shaners15]

Hey guys I have been following this forum for few months and now finally I have found the time to get this done. I need some help from you experts. It seems like there isn't ONE post that solidifies everything, therefore why I am asking such questions below. Your help will be greatly appreciated.

Question 1: Best sub floor insulation materials. (THE MAIN QUESTION) ---- I want to make sure I retain heat for few days after I fire it up, so that I can use the retained heat for some after cooking/baking. ALSO, I will need to move the oven in 1 year. So I am trying to build it so that later on I have some structural strength to move it. Thats why I am building a concrete floor that will go with the layers above it so it can all be moved.

I know I am trying to get best of all worlds. But if I am going to put in effort, I want it to last a long time and I wont have the time or energy to remake it. Money isnt an issue as long as its long lasting.

Option 1
From top to bottom:

Fire bricks (cooking surface) (will find and buy whatever is the standard thickness)
CaSI board 2"
Vermic/Cement 2"
Concrete floor 4" with rebars and all that good stuff.

OR Option 2

Fire bricks
CaSI board 2"
CasI board 2" (total 4")
Concrete floor 4"

OR Option 3

Fire bricks
castable heat bank 1"
CaSI board 2"
Vermic/Cement 2"
Concrete floor 4"

OR Option 4

Fire bricks
castable heat bank 1"
CaSI board 2"
CaSI Board 2"
Concrete floor 4"


Question 2: I am trying to build a WFO that can handle at least 2-3 - 10" pizzas at once. I want to be able to put a pan of full turkey. Multiple skewers. Multiple naan bread at once. Is the 42" dimensions as posted in the PDF sufficient?

Thanks for your help!!!!

[david s]

You don't say how big you plan to make your oven although your second question suggests you are planning on a 42". Remember the bigger the oven the heavier it will be which makes the relocation that much more difficult. A 20% increase in diameter results in over 70% increase in volume with a similar corresponding increase in mass, cost and labour. Casting in some lifting anchors into the supporting slab would be a good start. You'll probably need a crane.

Regarding your first question, you don't say that cost is a factor. Casting your own vermicrete is a pretty economical way to get decent insulation, but needs time for it to dry. Using foam glass is an excellent solution as it does not absorb water. The usual recommended floor thickness is 2" but if you want more thermal mass for heat storage go thicker, but realise more time and fuel is required to pump in the extra heat required.

"How many pizzas can you fit into the oven?" is an oft asked question. In reality most homeowners only cook one pizza at a time as it takes longer to prep than cook. I regularly cater for parties up to 50 people with my 21' mobile oven, although guests have to share whatever comes out of the oven. I can't however roast anything bigger than a 4Kg turkey, it's too tall for the door, but we regularly cook sourdough and roast meats for the family.

[Shaners15]

You don't say how big you plan to make your oven although your second question suggests you are planning on a 42". Remember the bigger the oven the heavier it will be which makes the relocation that much more difficult. A 20% increase in diameter results in over 70% increase in volume with a similar corresponding increase in mass, cost and labour. Casting in some lifting anchors into the supporting slab would be a good start. You'll probably need a crane.

Regarding your first question, you don't say that cost is a factor. Casting your own vermicrete is a pretty economical way to get decent insulation, but needs time for it to dry. Using foam glass is an excellent solution as it does not absorb water. The usual recommended floor thickness is 2" but if you want more thermal mass for heat storage go thicker, but realise more time and fuel is required to pump in the extra heat required.

"How many pizzas can you fit into the oven?" is an oft asked question. In reality most homeowners only cook one pizza at a time as it takes longer to prep than cook. I regularly cater for parties up to 50 people with my 21' mobile oven, although guests have to share whatever comes out of the oven. I can't however roast anything bigger than a 4Kg turkey, it's too tall for the door, but we regularly cook sourdough and roast meats for the family.

Hello david, thanks for your reply. Yes I was thinking around 42" will be a good size for diversity of cooking. Yours is 21"? Can you share a link to your build?

Second, you mentioned foam glass as a subfloor insulation. Given the template, how would my layers look then? Do I still need the CaSI and/or verm/con.

Overall having only 2" insulation is sufficient if its Casi or Foam? Or Does that leak alot of the heat?

Thanks for your help!!

[Petter]

I would do #2, in your case.

About heat retention, mass- and insulation thickness:
https://community.fornobravo.com/for...retic-apporach

About insulation material, pick your choice:
https://community.fornobravo.com/for...-matters-to-us

[JRPizza]

May want to consider a 39". I went back and forth trying to decide between a 36 and a 42 and hit on the idea (as others did before me) to go with a 39. I think it is a good compromise of not too big and not too small, and some of the numbers worked out very well which makes me think 39 might be the "ideal" size. I took the FB recommended sizes of door from a 36 and a 42" and interpolated to get a door height (see below). Notice the door height for 39" is very close to the ideal height of 63% - I took it as an omen . Also if you check out my build you can see that at 12.25 high and 19.5 wide you can make a perfectly half circle arch (@9.75 radius) that sits on a full brick (2.5"). Lastly a 39 gives you a brick OD of 48" (assuming standard build practices) and if you don't mind building right up to the edge of your boards you can often get a 48" width with either 1X2 or 1X 3 foot boards and minimize waste.

Inch	ID	Height	Door Width	Door Height	Ratio
36	36	18	19	12	66.67%
39	39	19.5	19.5	12.25	62.82%
42	42	21	20	12.5	59.52%

The bigger the oven is the more wood you are going to use to heat it, and the heavier it is going to be if you move it. In case you were wondering if 39" is big enough here is a picture of my oven cooking up two Thanksgiving turkeys in full size roasters side by side.

[Shaners15]

I would do #2, in your case.

About heat retention, mass- and insulation thickness:
https://community.fornobravo.com/for...retic-apporach

About insulation material, pick your choice:
https://community.fornobravo.com/for...-matters-to-us

Hey Petter, thanks for you response. I looked at that data I kind of got an idea. For the layer of "castable heat bank" is that not necessary? Are bricks alone sufficient? Thanks for your input!

[Shaners15]

May want to consider a 39". I went back and forth trying to decide between a 36 and a 42 and hit on the idea (as others did before me) to go with a 39. I think it is a good compromise of not too big and not too small, and some of the numbers worked out very well which makes me think 39 might be the "ideal" size. I took the FB recommended sizes of door from a 36 and a 42" and interpolated to get a door height (see below). Notice the door height for 39" is very close to the ideal height of 63% - I took it as an omen . Also if you check out my build you can see that at 12.25 high and 19.5 wide you can make a perfectly half circle arch (@9.75 radius) that sits on a full brick (2.5"). Lastly a 39 gives you a brick OD of 48" (assuming standard build practices) and if you don't mind building right up to the edge of your boards you can often get a 48" width with either 1X2 or 1X 3 foot boards and minimize waste.

Inch	ID	Height	Door Width	Door Height	Ratio
36	36	18	19	12	66.67%
39	39	19.5	19.5	12.25	62.82%
42	42	21	20	12.5	59.52%

The bigger the oven is the more wood you are going to use to heat it, and the heavier it is going to be if you move it. In case you were wondering if 39" is big enough here is a picture of my oven cooking up two Thanksgiving turkeys in full size roasters side by side.

WOW! Awesome JRPizza. That does seem like an ideal dimension. I will definitely strongly consider this. I am going to go through build and start putting the dimension plans together. What do you recommend for the subfloor insulation layers and if a heat bank under the bricks is needed?

Thanks!!!!

[Shaners15]

May want to consider a 39". I went back and forth trying to decide between a 36 and a 42 and hit on the idea (as others did before me) to go with a 39. I think it is a good compromise of not too big and not too small, and some of the numbers worked out very well which makes me think 39 might be the "ideal" size. I took the FB recommended sizes of door from a 36 and a 42" and interpolated to get a door height (see below). Notice the door height for 39" is very close to the ideal height of 63% - I took it as an omen . Also if you check out my build you can see that at 12.25 high and 19.5 wide you can make a perfectly half circle arch (@9.75 radius) that sits on a full brick (2.5"). Lastly a 39 gives you a brick OD of 48" (assuming standard build practices) and if you don't mind building right up to the edge of your boards you can often get a 48" width with either 1X2 or 1X 3 foot boards and minimize waste.

Inch	ID	Height	Door Width	Door Height	Ratio
36	36	18	19	12	66.67%
39	39	19.5	19.5	12.25	62.82%
42	42	21	20	12.5	59.52%

The bigger the oven is the more wood you are going to use to heat it, and the heavier it is going to be if you move it. In case you were wondering if 39" is big enough here is a picture of my oven cooking up two Thanksgiving turkeys in full size roasters side by side.

Hey JR I tried clicking that link in your signature. But its not working. Do you a have working link to your build? Thanks

[JRPizza]

Thanks for pointing out the bad link. The forum updated a while back and most of my bookmarked links got broken - forgot about my signature link, which I updated below..
I think any of the high tech insulation boards are great . I used a product called Insblok-19 as I could source it locally (no shipping) and got what I thought was a good deal on it. They had some 2.5 inch board on clearance and I went with 2 layers for 5". I probably would have just used 4" but it was cheaper to go with 5 .
Don't know about a heat bank. Some folks that want to cook many loads of bread with a single firing lay their bricks on edge so they have a 4.5 inch floor but I just went with the standard 2.5 and am plenty happy with it.
The beauty of this forum, if you are willing to put in the time, is the plethora of opinions and oven designs. I read many builds and found a few folks that I was comfortable emulating (copying) and followed their basic design as best as I could.
One last comment based on your first post above. I don't know of anybody here that cooks 3 pizzas at a time. They cook very fast and typically need to be rotated to keep from burning, so I usually just cook one at a time and even a heavily loaded pie cooks in less than 3 minutes. If you can cook 3 at a time without burning you are either a magician or your oven isn't hot enough

[Petter]

Hey Petter, thanks for you response. I looked at that data I kind of got an idea. For the layer of "castable heat bank" is that not necessary? Are bricks alone sufficient? Thanks for your input!

The calculations tell that a ratio of 1:2 to 1:3 is the best compromise between mass and insulation for a given thickness. In theory, they should be equal, but since heat retention time is constant (within some 90 %) across the given ratios, less mass and more insulation heat up faster with less wood.

I really doubt you would need additional mass under the firebricks. 2" bricks and 4-6" of insulation or 3" bricks and 6-9" insulation. Too thick floor only wastes wood during heat up.

[david s]

Hello david, thanks for your reply. Yes I was thinking around 42" will be a good size for diversity of cooking. Yours is 21"? Can you share a link to your build?

Second, you mentioned foam glass as a subfloor insulation. Given the template, how would my layers look then? Do I still need the CaSI and/or verm/con.

Overall having only 2" insulation is sufficient if its Casi or Foam? Or Does that leak alot of the heat?

Thanks for your help!!

2" of quality under floor insulation is considered sufficient, although you'll often hear the mantra "you can't have too much insulation" There is a point somewhere that you get little benefit from extra insulation (law of diminishing returns),

You won't find a build thread for my oven because our very kind forum hosts are oven manufacturers and have been kind enough to encourage home builders even though it may potentially affect their sales. My belief is that the more people who build, install and use WFO's the more the word is spread and therefore sales would be increased. I am sure that FB are of the same view. As I am also a small manufacturer it would be extremely rude as well as against the forum guidelines to be promoting my own product, so I don't have a build thread, but willing to impart all knowledge I've accumulated over the years in order to promote this wonderful "revolution". Apologies for the rave, here's a link to my kiln build which you may find of some interest.

https://community.fornobravo.com/for...kiln#post14564