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Help needed! can't get a good draw

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  • Help needed! can't get a good draw

    Hi all

    First time post but already uber impressed with the skills some of you have!

    Building my first oven, all gone quite well until I set the first fire................. the vent I cut in the front arch doesn't draw smoke effectively. (pic1)

    I have widened the gap and also chopped some of the internal side of the gap to make it more curved (pic2) but I still get smoke drifting out the front.

    However when I block the top of the entrance and put the large chimney on I get a really good draw and the fire roars (pic 3)

    Is there something I can change now? I'm currently planning to extend the front section of the arch to encourage the smoke to go up the vent and or building a door which would replicate the effect of the bit of ply I have in place now.

    But I'd rather not have to do that as when I would need to access the oven I'll still get a load of smoke in my face

    Any advice as to how I can not get smoke in my face would be very welcome.

    NB the dome hasn't had it's coat of render yet which is why is looks a little tatty..

    Thank you in advance

    Marc
    Attached Files

  • #2
    Re: Help needed! can't get a good draw

    Maybe I don't understand, but I believe you need a chimney and a door to get a proper draw. I did not try mine before had a chimney and door so I don't know for sure. I am in the process of building my final door (got the glass today!) so I used double thickness 3/4 exterior plywood for a test/seasoning door. I drilled a few 1" holes in the bottom to let air in.

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    • #3
      Re: Help needed! can't get a good draw

      That chimney needs to be sealed to where it will not draw air between the top of the arch and the bottom of the chimney. But, for the most part, IMO you need to try preheating the chimney before starting a fire in the WFO .
      I don't care what folks say behind my back........They are either braggin' or.......lyin'


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      • #4
        Re: Help needed! can't get a good draw

        If that is your first fire. a small fire just to start curing the oven then that is absolutely normal. Once you start bigger fires the heat generated will aid in the draw up the chimney. Right now your smoke is not that hot so it tends to just linger about. Once you get it hot it will want to rise. No worries your oven looks great. Get it cured as you should and I'll bet it will be fine.

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        • #5
          Re: Help needed! can't get a good draw

          Marc,

          When I built my outside arch, I dropped it about an inch. My thinking was that the smoke would hit it and prefer to back up and out. Not sure how much it helps but the smoke out the entry is a minimum. Once the temps get up it will definitely go out your vent. And as gulf mentioned, ensure that the stack is sealed.
          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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          • #6
            Re: Help needed! can't get a good draw

            Originally posted by Mingy View Post
            Maybe I don't understand, but I believe you need a chimney and a door to get a proper draw. I did not try mine before had a chimney and door so I don't know for sure. I am in the process of building my final door (got the glass today!) so I used double thickness 3/4 exterior plywood for a test/seasoning door. I drilled a few 1" holes in the bottom to let air in.
            So do you need a door to get a proper draw? I saw a post which had a you tube video which had very good draw with no door but was that the exception?

            Also I have done a few larger fires(2/3 logs) now and I still get smoke coming out of the front, do I need to shape the vent more?

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            • #7
              Re: Help needed! can't get a good draw

              Also new ovens are notorious for being smokey. Once it is dry, and this may take about ten fires it will be less smokey.
              Kindled with zeal and fired with passion.

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              • #8
                Re: Help needed! can't get a good draw

                Originally posted by Gulf View Post
                IMO you need to try preheating the chimney before starting a fire in the WFO .
                Its what his Great Great Great Grandpappy used to do, its a tradition.....
                The English language was invented by people who couldnt spell.

                My Build.

                Books.

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                • #9
                  Re: Help needed! can't get a good draw

                  The smoke will never flow correctly without a chimney. When the chimney is installed you will get some smoke out the front until the chimney heats up a bit and starts flowing upward from that heat. Heat rises, so when the chimney gets hot it actually starts to suck the air up into it which draws in the smoke. The taller the chimney, the more draw you will.
                  Last edited by Jaronimo; 05-25-2012, 04:25 AM. Reason: Error
                  http://cookinginmyyard.com

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                  • #10
                    Five points Marc

                    Welcome Marc
                    • The oven smokes only in the early stages of the fire, after it heats up, it does not smoke so much, expect that to improve when you get a hot fire in there.
                    • An air tight chimney will draw much better than your trial fitting does.
                    • A 'blast door' is something many of us use every time we light the fire.
                    • If you light the fire at the top of a stack of kindling, you may have less smoke in the early stages of your fire, search for 'top down' fire starting.
                    • Your oven entry is very shallow, that makes it easy to access the inside of the oven, but a little more tricky evacuating the smoke efficiently.
                    • HTH
                    This is my blast door, I use it for every fire:

                    Lee B.
                    DFW area, Texas, USA

                    If you are thinking about building a brick oven, my advice is Here.
                    Our One Meter Pompeii Oven album is here.
                    An album showing our Thermal Breaks is Here.

                    I try to learn from my mistakes, and from yours when you give me a heads up.

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                    • #11
                      Re: Help needed! can't get a good draw

                      Thanks again everyone - great to know I haven't built a dud!

                      More follow ups,

                      Lburou

                      Couldn't see you pic of a blast door - can you repost? just to double check this sits on the very front of the door - not in between the cooking area and the chimney like a cooking door? Do people have 2 doors ?

                      Gulf

                      How do I preheat a chimney?

                      Thank you guys

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                      • #12
                        Re: Help needed! can't get a good draw

                        This is my blast door. This is my insulating door.
                        Lee B.
                        DFW area, Texas, USA

                        If you are thinking about building a brick oven, my advice is Here.
                        Our One Meter Pompeii Oven album is here.
                        An album showing our Thermal Breaks is Here.

                        I try to learn from my mistakes, and from yours when you give me a heads up.

                        Comment


                        • #13
                          Re: Help needed! can't get a good draw

                          Originally posted by MarcMunier View Post
                          pic of a blast door -
                          Here is mine.
                          Attached Files
                          The English language was invented by people who couldnt spell.

                          My Build.

                          Books.

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                          • #14
                            Re: Help needed! can't get a good draw

                            The use of a so called "blast door" creates extremely efficient combustion, which leads to a very rapid rise in temp. This rise is likely to exceed 500 C/ hr which is really way to rapid for the safety of any refractory, especially from start up and is likely to cause premature (usually unseen) damage. Refractory materials are not particularly good heat conductors relative to materials like steel for instance. It takes around an hour for the heat to penetrate right through the brick so uneven expansion leads to stress on the refractory. To be kind to your oven it would be prudent to allow the temp to rise at a more reasonable rate, which means not using the blast door.
                            However in practice we usually want to get the oven up to operating temp as quick as possible. Just be aware that it is probably not doing your refractory much good pushing it this fast.
                            Last edited by david s; 05-25-2012, 06:09 PM.
                            Kindled with zeal and fired with passion.

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                            • #15
                              Re: Help needed! can't get a good draw

                              Originally posted by MarcMunier View Post

                              Gulf

                              How do I preheat a chimney?
                              I am not disagreeing with any of the info which has been given on this thread. This technique just helps get the most out of some bad situations. IE: windy days, days when smoke seems to lay close to the ground, days when your chimney is colder than the ambient temperature. If the ambient temperature of the outside air is higher than your oven or chimney then the air inside is cooler (heavier). Cooler air in your chimney will fall creating a natural down draft. If you light a fire under some of these conditions the smoke will take the least path of resistance, straight out your door opening which it is already trained to do. That is probably why blast doors work so well.

                              As far as preheating your chimney goes, it is a pretty straight forward approach and real cheap to prove or disprove. Think of it as training the smoke to go where you want it to. This is assuming that you have dry wood and kindling which are properly stoked in the oven/fireplace. (It definitely works for fireplaces)

                              In the conditions which I mentioned above, if you light a match and hold it up high in the flu you will notice the flame/smoke being pushed back down. It may take a second match, a lit piece of kindling, or a rolled up news paper to get this draw headed up your chimney. Once you see the smoke going the right way slowly lower your flame to the kindling set in you oven/fireplace. I like to have a little kindling set on top of my wood bundle and once that is going, light the kindling under the stack.
                              I don't care what folks say behind my back........They are either braggin' or.......lyin'


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