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Oven opening size - Forno Bravo Forum: The Wood-Fired Oven Community

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  • Oven opening size

    You are working to balance two conflicting requirements with your oven opening.

    First, the smaller the opening, the better your oven is at holding heat. If the size of the opening relative to the volume of the oven is too large, it will be difficult to keep your oven at high heat, and it won't hold heat for baking. There is a U.S. made commercial oven that has this problem, and I have heard numerous restaurant owners and pizza chefs complain about it. I had a small (26") oven at an Italian house, and the opening (16" x 10") was too large (relative to the oven volume), and it just couldn't hold heat.

    Second, the opening needs to be big enough to easily move food in and out of the oven. If the opening is too small, it can be a pain just using it. I have that problem with my Scott oven.

    For the opening width, 18"-19" is pretty standard. It gives you room to work (and as Robert says) see the fire, without over doing it. You can go a little wider, but I wouldn't go past 20". That width will let you get just about any pizza in and out of the oven.

    Opening height does depend on dome height, and 60% is an OK rule of thumb -- though it is something of an urban legend. There is no perfect formula, and I have never seen it used in the context of an Italian brick oven. For example, the ancient ovens have really high domes (you can almost stand up in them), so the opening height to dome height ratio on those is tiny. Equally, as brick ovens gets larger and the dome gets higher, there is no reason to make the opening taller than 12"-13" -- the size you need to get a roast in and out. So in that case the ratio of opening height to dome height gets smaller and the ovens simply perform better.

    If you have a 42" oven, with a 20" dome, an 19"W x 12"H opening should work nicely. Good access, good thermal characteristics.

    If you have a 36" oven with a 17"-18" dome, an 18"W x 11"H opening would be good.

    If you are building a Volta Bassa (low Naples style dome), you should bring your opening down an 1" or so -- but makes sure you can still fit in a turkey.

    If you want to maximize heat retention, you can always arch your oven opening (higher in the middle for a roast), but lower on the sides for heat retention.

    If you are really into maximum design, you can have a local metal fabricator make you a cast iron door opening like this:

    http://fornobravo.com/commercial_piz...istorante.html

    Wide at the bottom, high in the middle and closed in at the sides. Now that is cool.

    James
    Pizza Ovens
    Outdoor Fireplaces

  • #2
    Re: Oven opening size

    I am having an oven built as part of a backyard landscaping project. My agreement with the contractor calls for an oven with a 36" diameter, 18" vault and an opening 19" wide by 12" high.

    The dome is complete and it varies from the recommended dimensions. Although the diameter is 36", the opening is 12.75" high and 20.5" wide. The floor is also more uneven than I would like (the contractor did not lay any fireclay or sand on top of the vermiculite concrete.)

    My question is whether the actual dimensions are "close enough" to the ideal that it will work for pizza, bread and other foods, or should I ask the contractor to rebuild at the proper dimensions? I am inclined to just let it go, but thought I would ask for other opinions. If this is a major issue I want it fixed, but I do not want to make the fuss unless I really have to.

    Thanks

    Comment


    • #3
      Re: Oven opening size

      I think you will be okay. Worst case is you could put an angle iron frame in the opening if you are really concerned about it.

      I'd document your issue but try the oven first...I think it will be okay.

      Funny, I had just read James' old post on door sizing this morning!!!
      I'm looking at a door that's 20x12.5 inches and a dome height of 22 inches.

      Get a peel and slide it on the floor though....a rough floor could really be a PIA. Might be possible to grind down any rough edges but you want a smooth floor....

      Good luck!
      Sharing life's positives and loving the slow food lane

      Comment


      • #4
        Re: Oven opening size

        From what I read I think you'll be okay. I would try it and see what happens...

        Regarding grinding the floor. I think you want to be careful as a lot were doing this but after sanding the floors would tend to "pit" easier. I think it has to do with taking of the "hard" outer layer of the firebrick.

        I would just try to grind down any "high" spots where the bricks meet.

        just my 2 cents.

        Thanks
        Dick

        Comment


        • #5
          Re: Oven opening size

          12.75 for an 18 inch dome is a bit high but I think it will be fine...width is not a big issue...you could have the contractors mason run an arch ring of firebrick splits to narrow and shorten the opening...could be left full 1.25" on sides to give you and 18" wide door by 11.5" high...that door height is almost exactly at what is usually the recommended ratio of door height being 63% of the height of the dome
          Any chance of photos?
          Best
          Dutch
          "Making the simple complicated is commonplace; making the complicated simple, awesomely simple, that's creativity. " Charles Mingus
          "Build at least two brick ovens...one to make all the mistakes on and the other to be just like you dreamed of!" Dutch

          Comment


          • #6
            Re: Oven opening size

            Agreed. All sounds good. If you can slide a peel in there without getting stuck on an uneven brick, your golden!
            GJBingham
            -----------------------------------
            Everyone makes mistakes. The trick is to make mistakes when nobody is looking.

            -

            Comment


            • #7
              Re: Oven opening size

              How uneven is the floor? Mine is a lot more uneven than some around here, but it works fine.

              One option would be to remove the floor, sprinke some sand on there and then replace the bricks again. Fiddly, but not impossible - unless the floor is mortared down? This would probably be better than grinding the bricks.
              "Building a Brick oven is the most fun anyone can have by themselves." (Terry Pratchett... slightly amended)

              http://www.fornobravo.com/forum/f8/p...pics-2610.html
              http://www.fornobravo.com/forum/f9/p...nues-2991.html

              Comment


              • #8
                Re: Oven opening size

                This may seem like a stupid question.... but I'm curious. Is everyone building their transition a uniform height ? All the discussion is about the door opening. I am assuming that you are refering to the opening in the dome ( leaving the heating chamber). What if you put on an exterior door ? My current plans are to use a hindged door at the end of the transition or the exit of the oven. I have a door that is about 12.5 tall by 19 wide. My plan is to mount this in a frame (with hindges) at the exterior. Construct the transition with an arch taller than the door leading back to the oven ( best guess about 18 inches tall). The exit from the actual oven opening would be about 14 inches tall.
                This should leave me with a "chamber" too collect smoke and prevent it from exiting the front of the oven. In my mind, having the front door shorter than than oven exit should encourage the smoke to go up than chimney rather than out the front.
                Would I then build a 22.5 inch dome to match the 14 inch oven exit ? Or build a 20 inch dome to match the exterior door. I am planing to have a removable "interior" door as well for retained heat cooking.
                Last edited by brokencookie; 09-07-2008, 11:35 PM. Reason: large fingers, small keys
                Sharpei Diem.....Seize the wrinkle dog

                Comment


                • #9
                  Re: Oven opening size

                  Bruce, I have an issue with smoke at fire up and so I decided to try making one of the baffle doors that lets air in the bottom and makes the smoke go out the chimney because it has no where else to go. Attached is a photo. I made it out of 1/2" Hardibacker and some scrap shelf brackets as it was a prototype. It worked very well save when it reaches 550F the Hardi begins to break down and give off a bad smell. I will construct in steel.

                  Now to get to your door idea, how will you get the inner insulating door thru the smaller outer door? Not saying it couldn't be done but it will take some clever designing. It is something I have and am considering but at the moment the smoke blocking door seems to work quite well. Perhaps too well as it ducts the incoming air such that it is like someone continually blowing on the fire. It burned wood fast; what would take an hour to burn down normally in about 40 minutes. The heat rose fast as well which for a brick oven might be a downside, with my steel dome I wasn't too concerned.
                  Wiley
                  Attached Files

                  Comment


                  • #10
                    Re: Oven opening size

                    Originally posted by Wiley View Post

                    Now to get to your door idea, how will you get the inner insulating door thru the smaller outer door? Not saying it couldn't be done but it will take some clever designing. Wiley
                    Wiley
                    I figure if I make transistion about 3 inches wider than the actual opening and make the actual oven opening the same size ( only about 2 inches taller). I should be able to insert a door at an angle, and then stand it up to block the entry.
                    The "inner' door is actually sort of a back up plan. I am planning to make a a full closure damper in the chimney, at which point the outer door will work for air control. If my plan doesn't work, then I will have to make and inner door. I am just trying to make all my design mistakes now rather than during the build.
                    Sharpei Diem.....Seize the wrinkle dog

                    Comment


                    • #11
                      Re: Oven opening size

                      Bruce, I think I understand what you are getting at. It seems most people try to contain the ovens heat within the oven area itself rather than include the entry area. I can see some downsides to including the entry, the biggest being the fact that it wasn't heated in the fireup so as the WFO "normalizes" there will be greater overall temperature drop ....the heat used to heat the previously unheated entry.

                      I too am planning on being able to shut off the chimney from the airflow when "closing up" for the night and wanting to retain heat for the next days cooking. My plan is to remove the chimney and insert a plug in the hole. I have designed my WFO so the chimney can easily be covered for storms and periods of non use. To do this easily means simply lifting off the chimney and inserting the plug/cap. This will lessen the loss from the chimney as the uninsulated direct path to the outside world for heat from my dome is thru the entry and thru the refractory which is part of both the dome and the chimney.

                      So I will have a door for the oven itself and a plug for the chimney. I'll probably set the smoke door mentioned previously in place both as a place to store it and to keep the passing raccoon from finding the warm area too inviting and so wanting to curl up and make himself at home :-)

                      Wiley

                      Comment


                      • #12
                        building an oven, my first posting

                        Hello,
                        I was inspired by this site to build an oven too. My husband and I are very excited about it. We have the base nearly complete and are finding lots of tips from the postings here. I am working with a contractor who has never built a pizza oven before so we are all learning together. The brickyard that sells the firebricks told him that he should use common clay bricks because they retain the heat better. This is completely contrary to the FB instructions, which clearly call for firebricks? Also, what is insulating concrete?
                        Thanks,
                        Connie

                        Comment


                        • #13
                          Re: Oven opening size

                          Definitely use firebricks.
                          Your local brick yard should have them in stock. ( I found them at ACME for $1.11 each, I used about 220 bricks.)
                          They tend to be yellowish in color. But can also be found in lighter reds.


                          Insulating concrete is made of a mixture of Portland Cement (not Quikrete), and vermiculite/perlite. Portland comes in 94lb bags and can be found at Lowe's or Home Depot. Vermiculite/perlite comes in 4 cubic foot bags. It is usually found at garden/horticulture stores or at local pool supply outfits.

                          The normal ratio for insulating concrete is 5 parts vermiculite to 1 part Portland cement. (by volume)
                          Mix the two together first, and then add enough water until it holds together.

                          The structural concrete should be poured first, followed by the insulating concrete. I would suggest that you pour a 5 1/2 inch insulating layer.

                          After it "hardens" after a few days, (it will feel like cork) then begin laying your hearth layer.

                          Good luck!

                          And we enjoy pics around here!

                          Dave
                          My thread:
                          http://www.fornobravo.com/forum/f8/d...ress-2476.html
                          My costs:
                          http://spreadsheets.google.com/pub?k...Xr0fvgxuh4s7Hw
                          My pics:
                          http://picasaweb.google.com/dawatsonator

                          Comment


                          • #14
                            Re: Oven opening size

                            Thank you so much for the answer to my question. I will post pictures of our progress soon.

                            Comment


                            • #15
                              how about the vent opening

                              Can anyone tell me what size vent opening I should have for a 11.5" x 19" opening on a 36" oven with a dome height of 20"?
                              Thanks!

                              Comment

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