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1" of Thermal Mass VS. 1" of Insulation

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  • 1" of Thermal Mass VS. 1" of Insulation

    I'm close to finishing my dome and I'm trying to decide whether to clad it with an inch of HeatStop mortar for thermal mass or use that inch for extra insulation blankets/loose vermiculite.



    I really like the idea of cooking the next day without re-firing the oven.

    Will the extra inch of mass make a big difference in the performance of the oven or would it be splitting hairs? Would I be better off using that inch for insulation?

    Also, will cladding the oven make it more susceptible to cracking?

    Thanks!
    Last edited by Ken524; 10-23-2007, 06:51 AM. Reason: Added photo
    Ken H. - Kentucky
    42" Pompeii

    Pompeii Oven Construction Video Updated!

    Oven Thread ... Enclosure Thread
    Cost Spreadsheet ... Picasa Web Album

  • #2
    Re: 1" of Thermal Mass VS. 1" of Insulation

    Hey Ken,

    I added about 1/2" - 5/8" of heat stop and then topped it with a 2" blanket and 3" vermiculite concrete. I didn't add the heat stop for added mass, just to give it a smooth/even finish before moving on.
    I then finished with 1" of Type N mortar and my mosaic tile.
    YES, after every pizza bake (usually late afternoon or evening) I am able to roast something the next day. I usually leave the coals in the oven and close the door overnight...the temp is usually in the 350 degree range the next morning and will hold round or above 300 for most of the day - If i keep the door in place. My door seals well but is not insulated. I think some sort of insulated door would really help, but I am pretty happy with what I have.

    RT

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    • #3
      Re: 1" of Thermal Mass VS. 1" of Insulation

      I hope you don't mind me butting in here, but I've been wondering the same thing. To clad or not to clad?
      Another question I've got: is the cladding structural i.e. does it make the oven stronger? (Obviously less of an issue on your oven Ken than on mine...)

      Just from gut feeling, I would have thought an oven would be more likely to crack with cladding.
      "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

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      • #4
        Re: 1" of Thermal Mass VS. 1" of Insulation

        An inch is really a lot of mass. You could probably get by with 1/4" if you really want to clad it. You'll already probably have longer firing times due to your use of medium duty bricks. If free space is a concern then I'd lean towards the insulation.
        Oven Progress
        Bread Photos
        Oven Stand Thread

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        • #5
          Re: 1" of Thermal Mass VS. 1" of Insulation

          Good question Ken.

          I was wondering the same thing. So I guess my mess of mortar on the outside will suffice!
          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

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          • #6
            Re: 1" of Thermal Mass VS. 1" of Insulation

            Thanks Ron,

            I forgot to add that piece of the puzzle:

            Originally posted by rlf5 View Post
            You'll already probably have longer firing times due to your use of medium duty bricks.
            So, the medium duty bricks will retain the heat longer? Is that because they are more dense?
            Ken H. - Kentucky
            42" Pompeii

            Pompeii Oven Construction Video Updated!

            Oven Thread ... Enclosure Thread
            Cost Spreadsheet ... Picasa Web Album

            Comment


            • #7
              Re: 1" of Thermal Mass VS. 1" of Insulation

              I think they have a higher aluminum content, but I'm not totally sure. The composition is different from light duty though. If you don't have any cracks I woudn't worry about it at all....or I'd just apply a thick coat to the joints to make sure.
              Oven Progress
              Bread Photos
              Oven Stand Thread

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              • #8
                Re: 1" of Thermal Mass VS. 1" of Insulation

                I definitely think that you should put that space into more Insulfrax. At a half brick your dome is already thicker than a commercial Italian pizzeria oven -- many of which bake bread every morning from retained heat.

                Sometime I think that the Bread Builders book got everybody off on the wrong foot regarding oven thickness and mass. I remember building my barrel vault oven and thinking "cool, the walls are 9" thick; it must be better than those lighter ovens." Years of experience later, I figured out the different demands of a commercial bakery and a home chef.

                Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.
                Pizza Ovens
                Outdoor Fireplaces

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                • #9
                  Re: 1" of Thermal Mass VS. 1" of Insulation

                  On the firebrick topic, the medium duty bricks have a slightly higher alumina content, so they are more heat resistent and more efficient at absorbing heat, but that does not translate into better heat retention. Conductivity works in both directions -- faster heat up and faster cool down. That is good for live fire cooking such as pizza, where you want your oven to recharge as efficienty as possible from the fire to maintain high heat. It has very little impact on retained heat cooking, such as bread and roasting.

                  I want to emphasize again how good these ovens are at retained heat cooking. You will be amazed and you will be able to bake more bread than your entire neighborhood will be able to eat! :-) You don't need more mass.

                  James
                  Last edited by james; 10-23-2007, 10:23 AM.
                  Pizza Ovens
                  Outdoor Fireplaces

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                  • #10
                    Re: 1" of Thermal Mass VS. 1" of Insulation

                    Originally posted by james View Post
                    Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.
                    Great news. Thanks for the advice James. The dome stays clean.

                    What I plan on doing is throwing on the blankets, curing, then building the enclosure. That way, in the event of Cracking During Curing (CDC), I'll be able to deal with it.

                    James, I think I can squeeze in 3" of blanket insulation. Does Insulfrax come 2" thick or only 1"? How far will a 50sqft roll go for a 42" dome?

                    Thanks
                    Ken H. - Kentucky
                    42" Pompeii

                    Pompeii Oven Construction Video Updated!

                    Oven Thread ... Enclosure Thread
                    Cost Spreadsheet ... Picasa Web Album

                    Comment


                    • #11
                      Re: 1" of Thermal Mass VS. 1" of Insulation

                      Hi Ken,

                      I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.

                      It turns out that 1" is the most widely produced thickness, so it is best to just run multiple layers. Overlap the seams, and it will work well.

                      Two boxes should give you three layers (just about). Go thicker on top, as there is more heat up there.

                      Have fun!
                      James
                      Pizza Ovens
                      Outdoor Fireplaces

                      Comment


                      • #12
                        Re: 1" of Thermal Mass VS. 1" of Insulation

                        Originally posted by james View Post
                        Ken and Dave, the good news is that your ovens have a lot of mass and will still heat up quickly. You're there! Insulate the heck out of it, and you are ready to go.
                        That's great to hear James!

                        I was getting all worked up for a coat of mortar.... and lots of mixing!

                        WOOHOO!

                        Arch and entry way for me!

                        Thanks for the input everyone.
                        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


                        • #13
                          Re: 1" of Thermal Mass VS. 1" of Insulation

                          You can still do a thin coat to seal up the oven, and give it a little structural integrity. You can just put it on with a trowel -- no heavy lifting.
                          James
                          Pizza Ovens
                          Outdoor Fireplaces

                          Comment


                          • #14
                            Re: 1" of Thermal Mass VS. 1" of Insulation

                            Originally posted by james View Post
                            Hi Ken,
                            I am going through the CDC phase right now, and I am patching the external cracks as I go. I am catching the hairline cracks each day as they appear, and so far, have kept them from getting bigger. We'll see.
                            Are you patching the external cracks with RefMix or some sort of high temp goo?
                            Ken H. - Kentucky
                            42" Pompeii

                            Pompeii Oven Construction Video Updated!

                            Oven Thread ... Enclosure Thread
                            Cost Spreadsheet ... Picasa Web Album

                            Comment


                            • #15
                              Re: 1" of Thermal Mass VS. 1" of Insulation

                              RefMix. It sets fast, which really helps. Make sure the oven is fully cooled down, and wet the area you are patching before you slop it on.
                              James
                              Pizza Ovens
                              Outdoor Fireplaces

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