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New guy with smoke and heat question...

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  • #16
    Re: New guy with smoke and heat question...

    Flue at the top of dome: Really bad practice, impossible to reach heat with a reasonable amount of wood, impossible to do retained heat cooking, but shouldn't effect draw.

    I am extremely suspicious of a four inch round flue for a 42 inch square oven. Even with that long a chimney, that's going to belch smoke on startup. FB recommends an eight inch flue, almost three times the area for a 42 inch round oven. Also there's no transition, just the four inch hole in the top.

    What would I do? Well your options aren't great. I'd start by blocking up that useless little hole at the top of the dome. You could build out your oven floor and build a proper firebrick entry with an eight inch flue at the recommended 2/3 height of the cooking chamber. Faith's idea is a good one as well: Have a stainless hood fabricated, and vent with stainless flue units, which could be elbowed to go through your existing hole in the roof. This is less than ideal because it puts a blisteringly hot hood at forehead height while you're cooking. Perhaps the fabricators could make a double layer hood that could be filled with loose vermiculite.

    You obviously spent a ton of money on this project. You would expect someone selling modular ovens would have at least some idea of how an oven works. If they don't know where and how an oven vents, I'm wondering if they know anything about insulation.
    My geodesic oven project: part 1, part 2

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    • #17
      Re: New guy with smoke and heat question...

      Can you integrate an exhaust fan into the 8" flue?

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      • #18
        Re: New guy with smoke and heat question...

        I don't know if an exhaust fan in the flue would help much because your still dealing with the 4 " restrictive oven opening. I would also be concerned about heat issues on the fan it's self and would need to check the heat operating range of the fan.

        As far as the vent hood goes I think you could get away with placing it higher then forehead height. I think if you went up some it would be fine. The pan shape of the covered area looks like a great place to trap smoke and in turn make the vinyl look dingy in short time so a vent hood would help even after the chimney is fixed.

        I know this idea sucks but I would think that 4" hole needs to be fixed by taking down the chimney and cutting a larger hole then rebuild the chimney. I don't know if that is the right answer but it is what I would do.

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        • #19
          Re: New guy with smoke and heat question...

          Can you integrate an exhaust fan into the 8" flue?
          You could but you shouldn't need to. A through-the-ceiling run of 8" flue should draw like a locomotive. Exhaust fans are used in commercial locations where there needs to be a long horizontal run of flue.

          As multiple posters have pointed out, it's the four inch hole. It's the wrong size and it's in the wrong place.
          My geodesic oven project: part 1, part 2

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          • #20
            Re: New guy with smoke and heat question...

            Before you start pulling that oven apart, why not try firing it some more. If it is new and wet it will smoke more. Although the 4" restriction is not helpful at start up, if it has an 8" flue beyond the 4" restriction, the flue should draw pretty well once it has heated up. Keep the fire small enough so it won't smoke, for at least half an hour. This should be enough time to heat the flue which will create drawing power. Presumably the manufacturer has sold plenty of these ovens and they work. Contact them for assistance before jumping in to rebuild.
            Kindled with zeal and fired with passion.

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            • #21
              Re: New guy with smoke and heat question...

              Thanks for all the good feedback. Needless to say I am less than happy right now as I did spend a ton of money and right now this oven is a pretty paperweight.

              I need to find a solution.

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              • #22
                Re: New guy with smoke and heat question...

                Originally posted by david s View Post
                Although the 4" restriction is not helpful at start up, if it has an 8" flue beyond the 4" restriction.
                I'm not sure it works that way. It's like feeding a 2 inch water pipe from 1/2 inch. Does nothing for the volume at the output. I would personally take off the flue and use an angle grinder to get it to a proper size. Remove the restrictor plate if you will (for you NASCAR fans). You still have the issues that David (Dmun) pointed out in regard to the location of the vent. I find it a little amusing that it was built by Stone Age manufacturing in Oklahoma (sorry).
                Last edited by Les; 06-02-2011, 06:10 PM.
                Check out my pictures here:
                http://www.fornobravo.com/forum/f8/les-build-4207.html

                If at first you don't succeed... Skydiving isn't for you.

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                • #23
                  Re: New guy with smoke and heat question...

                  Why do you find it amusing? Fill me in.

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                  • #24
                    Re: New guy with smoke and heat question...

                    Apart from remodeling the oven the exhaust fan you linked to may be the go.

                    As a rule of thumb the flue shouldnt be less than 10% of the oven/fireplace opening size to work efficiently, more than 10% is better.

                    Edit.
                    I just looked at your flue pic, how far from the top of the flue is the rain stopper?
                    Is it too close and stopping the smoke?
                    Last edited by brickie in oz; 06-02-2011, 08:48 PM.
                    The English language was invented by people who couldnt spell.

                    My Build.

                    Books.

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                    • #25
                      Re: New guy with smoke and heat question...

                      Originally posted by NYC View Post
                      Why do you find it amusing? Fill me in.
                      Stone age - like not understanding physics - Oklahoma, nuff said. (I am not slamming the good people from OK - it's just embedded in the American vernacular)
                      Check out my pictures here:
                      http://www.fornobravo.com/forum/f8/les-build-4207.html

                      If at first you don't succeed... Skydiving isn't for you.

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                      • #26
                        Re: New guy with smoke and heat question...

                        Originally posted by Les View Post
                        I'm not sure it works that way.
                        Me too, its not like a venturi in a carburetor that has a sucking force of an engine to draw the smoke.
                        The smoke will find the easiest way out which is the oven opening.
                        The English language was invented by people who couldnt spell.

                        My Build.

                        Books.

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                        • #27
                          Re: New guy with smoke and heat question...

                          Do you guys feel that a larger chimney diameter would work or would it cause too much heat loss? Do I need to modify the chimney or completely change the design to an igloo with the chimney over an extended opening?

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                          • #28
                            Re: New guy with smoke and heat question...

                            Originally posted by david s View Post
                            Before you start pulling that oven apart, why not try firing it some more. If it is new and wet it will smoke more. Although the 4" restriction is not helpful at start up, if it has an 8" flue beyond the 4" restriction, the flue should draw pretty well once it has heated up. Keep the fire small enough so it won't smoke, for at least half an hour. This should be enough time to heat the flue which will create drawing power. Presumably the manufacturer has sold plenty of these ovens and they work. Contact them for assistance before jumping in to rebuild.
                            Victorian era fireplaces often had an adjustable entry into the chimneys so that not too much heat got lost once the fire and chimney were hot. You could reduce the enry adjustment and the fire still drew well, but at start up you had to have it wide open to prevent smoking the room. I think this is the situation with this oven, although it has no adjustment for start. Presumably the manufacturers designed it this way so not so much heat gets lost up the chimney.
                            Kindled with zeal and fired with passion.

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                            • #29
                              Re: New guy with smoke and heat question...

                              Originally posted by NYC View Post
                              Do you guys feel that a larger chimney diameter would work or would it cause too much heat loss? Do I need to modify the chimney or completely change the design to an igloo with the chimney over an extended opening?
                              Thats a significant modification. Opening up the hole size should be fairly straight forward. If you could install some type of damper to retain the heat, it would help. Although not ideal, it should allow the oven function.
                              Check out my pictures here:
                              http://www.fornobravo.com/forum/f8/les-build-4207.html

                              If at first you don't succeed... Skydiving isn't for you.

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                              • #30
                                Re: New guy with smoke and heat question...

                                NYC,
                                Is the whole chimney length 8" with just the restriction at the entry to it? Or is the 8" bit only at the top?
                                If the major length of the chimney is the 4" diam. you'll have to go bigger.
                                Call the manufacturer of the oven. Did they specify a 4" flue pipe?
                                Last edited by david s; 06-04-2011, 01:35 AM. Reason: 4" not 6"
                                Kindled with zeal and fired with passion.

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