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Looking for acurate Rumford measurements

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  • Looking for acurate Rumford measurements

    Hi all,

    A recently found out about the Rumford design am very enthusiastic to use it for a smaller, outside fireplace using perhaps different materials than your normal masonry fireplace.

    I have searched high and low and it is very difficult to get clear, complete and unambiguous scientific specs about the size, area and interrelations of the Rumford fireplace concept when disregarding masonry and building code restrictions or conventions for a moment.

    My main questions are these:

    1. What is the relation (ratio) between the INNER measurements of the
    throat opening, the front of the fireplace and the surface area of the
    smoke chamber and the surface area of the chimney?

    2. Is the smoke chamber important at all for the efficiency of the fire?
    or is it merely an artefact from having to connect the wide fire place
    to a smaller chimney, while still accommodating the narrow throat
    opening?

    3. Could one, in theory, completely do without a separate smoke chamber
    and have the throat go over into a chimney straight away? Is a larger
    area right about the throat required for the Venturi effect?
    If so, what is the minimum ratio of throat-to-smoke chamber area to get
    an effective fire?


    I have been experimenting with smaller Rumford fireplaces for outside and have
    created a Rumford Calculator in Excel (click here to download) to help with different
    sizes. I now realise the Calculator is probably off the mark
    considerably.

    I have included pictures of the first two quick trails and I am in the
    process of building me first real prototype, roughly 21.5" (55cm) wide

    You see, for the measurements I have gone of the plans that can be found
    on Rumford Fireplaces, combined with other information, comments and ratios found
    elsewhere.

    The problem I now realise, is that most Rumford builders on the web approach the design from a builders
    perspective, with the measurements of bricks, standard flue liners and building codes first in mind.

    This is understandable of course, but for the most, the mention the OUTSIDE measurements of flue tiles and throat, which is not helpful when trying to figure out what the INSIDE measurements should be.
    I would love to have more definitive INNER area measurements and the relationship between them. Also, because my fireplace will be on the small side, the margin of error is smaller and of importance i think.

    As a part-time engineer and weekend-inventor, I am keen to get the measurements right.
    I am very keen and willing to experiment with different materials to
    make the fireplace as small and light as possible and have clear
    boundaries for the thermodynamic principles at work would be essential I
    feel.


    If anyone would like to share the ratios and margins of error when it comes to throat, smoke chamber and chimney my fireplace will be a roaring (sorry) success and I am for ever in your debt and will sing the
    praise of Count Rumford all this summer!

    Cheers,

    thijs
    Attached Files
    Last edited by thijsatteiltje; 10-22-2013, 11:41 PM. Reason: Reason for posting was unclear.

  • #2
    Re: Looking for acurate Rumford measurements

    If you have read about the Rumford design you know what is required to make the fireplace work.

    Dont try to reinvent the wheel.
    The English language was invented by people who couldnt spell.

    My Build.

    Books.

    Comment


    • #3
      Re: Looking for acurate Rumford measurements

      Al,

      fully agree with you. Sorry if I was not clear.

      My intention is not to experiment with the design, just with building materials (as availability and price are a factor, plus it is fun to come up with something unique)

      But I have searched high and low and it is very difficult to get clear, complete an unambiguous specs about the size, area and relations of the different components.

      I even have the old Count's papers somewhere but those also require some interpretation.

      Someone might mention he uses a throat that is 4 inches deep, but then fails to mention how wide it is (not to mention most throats are trapeziod shaped)

      So what I am curious about, are the design specification for a Rumford based on airflow, pressure, expansion of gasses, venturi effect and how the column of rising gasses in the flue behaves.

      Cheers,

      Thijs

      Comment


      • #4
        Re: Looking for acurate Rumford measurements

        Originally posted by thijsatteiltje View Post
        Hi all,



        I have been experimenting with smaller Rumford fireplaces for outside and have
        created a Rumford Calculator...........to help with different
        sizes. I now realise the Calculator is probably off the mark
        considerably.


        That is because an outside fireplace doesn't function like an inside fireplace, because of the infinite variables which effect draw outside.
        Old World Stone & Garden

        Current WFO build - Dry Stone Base & Gothic Vault

        When we build, let us think that we build for ever.
        John Ruskin

        Comment


        • #5
          Re: Looking for acurate Rumford measurements

          Rumfords are not really suitable for a true outdoor fireplace, although they work fine for a protected, covered outside area. Even then a modified Rumford will perform better than a true rumford.

          Comment


          • #6
            Re: Looking for acurate Rumford measurements

            Originally posted by Tscarborough View Post
            Rumfords are not really suitable for a true outdoor fireplace, although they work fine for a protected, covered outside area. Even then a modified Rumford will perform better than a true rumford.
            What mods ?
            I'm planning on building an outdoor one, and will reduce the height of the opening slightly as per the rumford site.
            Am also planning on casting my own throat and smoke chamber as postage to australia is exxy.
            Would anyone with experience know what material would be best ?
            Would a castable insulator be better than refractory material for example ?
            My Build:
            http://www.fornobravo.com/forum/f51/...and-19101.html

            Comment


            • #7
              Re: Looking for acurate Rumford measurements

              A modified Rumford has different firebox dimensions ( ie: deeper wider firebox
              ) than a true Rumford, which is tall and shallow in depth. But it is not built like most modern, cavernous fireboxes built today.
              Old World Stone & Garden

              Current WFO build - Dry Stone Base & Gothic Vault

              When we build, let us think that we build for ever.
              John Ruskin

              Comment


              • #8
                Re: Looking for acurate Rumford measurements

                The entire Rumford design, both regular and modified can be built with standard firebrick, no need to cast anything.

                For dimensions and design of both: Rumford Fireplaces

                Comment


                • #9
                  Re: Looking for acurate Rumford measurements

                  Here is one I built for myself at home last year, no fancy cutting in the throat, it draws like a beauty and kicks out tons of heat.
                  FYI the opening is 1600mm wide and 900mm high at the the top of the intrados.
                  Attached Files
                  Last edited by brickie in oz; 10-22-2013, 11:27 PM.
                  The English language was invented by people who couldnt spell.

                  My Build.

                  Books.

                  Comment


                  • #10
                    Re: Looking for acurate Rumford measurements

                    Originally posted by stonecutter View Post
                    A modified Rumford has different firebox dimensions ( ie: deeper wider firebox
                    ) than a true Rumford, which is tall and shallow in depth. But it is not built like most modern, cavernous fireboxes built today.
                    My idea was for a rumford 900mm wide, 800mm high and 400deep with a 400 wide back wall. How much can I deepen and widen it ?
                    My Build:
                    http://www.fornobravo.com/forum/f51/...and-19101.html

                    Comment


                    • #11
                      Re: Looking for acurate Rumford measurements

                      Originally posted by Tscarborough View Post
                      The entire Rumford design, both regular and modified can be built with standard firebrick, no need to cast anything.

                      For dimensions and design of both: Rumford Fireplaces
                      If I don't have a cast throat section then I'd need a steel lintel to support the bricks ? Haven't seen any all brick ones on the rumford site, nearly all are the bought cast sections and a few who have cast their own.
                      My Build:
                      http://www.fornobravo.com/forum/f51/...and-19101.html

                      Comment


                      • #12
                        Re: Looking for acurate Rumford measurements

                        Originally posted by brickie in oz View Post
                        Here is one I built for myself at home last year, no fancy cutting in the throat, it draws like a beauty and kicks out tons of heat.
                        FYI the opening is 1600mm wide and 900mm high at the the top of the intrados.
                        That's an awesome looking fireplace. How deep is it ?
                        Any chance you could draw one of your rough sketches of the throat design ( a X- section ) ??
                        My Build:
                        http://www.fornobravo.com/forum/f51/...and-19101.html

                        Comment


                        • #13
                          Re: Looking for acurate Rumford measurements

                          Originally posted by seamad View Post
                          That's an awesome looking fireplace. How deep is it ?
                          Any chance you could draw one of your rough sketches of the throat design ( a X- section ) ??
                          9 posts and you know of my rough sketches? How bizarre....

                          A rough one then it is.....
                          Attached Files
                          Last edited by brickie in oz; 10-23-2013, 12:19 AM.
                          The English language was invented by people who couldnt spell.

                          My Build.

                          Books.

                          Comment


                          • #14
                            Re: Looking for acurate Rumford measurements

                            Originally posted by seamad View Post
                            What mods ?
                            I'm planning on building an outdoor one, and will reduce the height of the opening slightly as per the rumford site.
                            Am also planning on casting my own throat and smoke chamber as postage to australia is exxy.
                            Would anyone with experience know what material would be best ?
                            Would a castable insulator be better than refractory material for example ?
                            seamad,

                            would be interesting to share notes on this. I have been experimenting with different heat resistant mixes myself over the years. A lot of the stuff that is readily available in the US is just ridiculously expensive over here (or not available at all)

                            Casting the throat can be a challenge in itself. The best approach I have found so far is explained here:
                            Richards Rammed Earth
                            Just build the fireplace out of brick and make the curved section of the throat out of ferrocement (chickenwire and rebar)
                            A mix of 1:2 portland cement/plaster sand on three layers of chickenwire is surprisingly heat resistant.

                            I have tried this myself (adding 0.5 part lime putty to a 1:3 portland/sand mix to make it easier to sculpt) and so far so good.

                            Here is some research into the fire resistant behaviour of ferrocement:
                            www.doaj.org/doaj?func=fulltext&aId=1465260‎

                            here is another forum discussion about alternative throat designs:
                            Casting Rumford Throat - Masonry - Contractor Talk

                            As for casting, I have not tried this yet but three sources on the web seem to confirm that this is the best homemade recipe:
                            Homemade furnace refractories
                            Making DIY Refractory For Your Foundry Furnace.

                            2/1.5/2/1.5 (fireclay/portland/silica sand/perlite)

                            But, in the examples given (foundry from melting metal) this mix is cast into a container and the final form is thick and solid. The throat on a rumford has thin, curved walls, so it can't be to brittle.

                            I would probably stick with the ferro cement, or, add some reinforcing metal mesh to your casting.

                            Let me know how you get on.

                            Cheers,

                            thijs

                            Comment


                            • #15
                              Re: Looking for acurate Rumford measurements

                              Originally posted by brickie in oz View Post
                              9 posts and you know of my rough sketches? How bizarre....

                              A rough one then it is.....
                              I've been a' lurkin awhile.
                              Thanks for the sketch, like you sailor soldier one the best
                              My Build:
                              http://www.fornobravo.com/forum/f51/...and-19101.html

                              Comment

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