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Question about vent - Forno Bravo Forum: The Wood-Fired Oven Community


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Question about vent

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  • Question about vent

    Hey there,

    I noticed that some ovens have vents in the front, others in the middle, and others in the rear. What are the pro's and cons to each?

    Also, I noticed for most ovens, there are smoke stains on the outside which leads me to believe that the front vents aren't working well much of the time. I dislike getting smoke in my face because you can't taste the food as well if you've beeen breathing in your nose.

    Any suggestions would be helpful.


  • #2
    vent location

    I think you will find that all brick ovens vent from the front, but the flues can be tilted to give a middle or rear chimney position, for aesthetic or clearance reasons. The conventional wisdom is that a straight vertical path is the best for chimney draw.

    The only member we've heard about who is unhappy about his draw is Robert Musa, who attributes it to not having enough of a funnel shape above the door opening. I'll leave specific comments on chimney draw to those who actually have built one. In general, a taller chimney draws better.
    My geodesic oven project: part 1, part 2


    • #3
      Smoke escapes only on start up.

      (M) Hi, Mike,

      (M) I am speaking *only* from my experience which is that smoke escapes from my oven entrance only when the oven is cold and not drawing well. That is invariably when I first start my fire. An uncooperative breeze can exacerbate this problem. Once the fire is hot, I get almost no smoke period; not even out the chimney.

      (M) I suspect that other bulders have had similar experiences but I've seen no postings yet supporting this probably unavoidable occurance. To mitigate it's occurance I build my starting small fire very carefully with only small, perfectly dry pieces of kindling. Even then, I will get some smoke escaping and it does discolor the front of my housing. The image I plan to post on Thursday of the front of my oven will not show the discoloration. That's because I repainted just before taking the picture. I painted the HardiPlanks a flat black (as opposed to the rest of the yellow housing) to act as a Trompe L'oile (sp?) which, from a distance, should create the illusion of a large semi-circular oven entry when in actuality, the opening is 1/2 that size.

      (M) Get your kindling securely started and walk away for 10 minutes. When you come back, slowly add larger dry pieces and you should be able to bake without any smoke in your eyes.


      "Everything should be made as simple as possible, ...
      but no simpler!" (Albert Einstein)


      • #4
        A builder told me that the Naples ovens have the vent run back over the top of the dome, then straight up from the center, because the hot air of the exhaust helps keep the dome hot.


        I'm not sure if that is an urban legend or not, but even if it's true I don't think it's worth the extra effort.

        Pizza Ovens
        Outdoor Fireplaces


        • #5
          not an urban legand....


          some folks are saying that the vent should hook back. So if you go this route then you want to have your refractory around this vent to force the heat down to the dome then you will want to insulate, insulate, insulate to keep it there.

          Might be easier to use the flue gas as a co-gen station to heat your jacussi instead.

          unless you are a member then you can't see the pics. I am not a member but when the thread was only 5 pages long I was able to get the pics...
          Attached Files


          • #6
            Hey Patrick,

            I know that some builders say you should do it, I think the urban legend part is whether or not it really helps.

            There are zillions of wood-fired brick ovens in Italy, and an incredibly tiny percentage (that's a scientific term) of them have the vent style where you bring the chimney back over the dome. Perhaps a few thousand out of a few million brick ovens. There are a few folks out there lost in the weeds of Pizza Napoletana, who don't seem to understand how you really use a brick oven. It's too bad, because they are confusing a lot of people.

            At the very most I would only consider doing this design if I were going to run a Pizza Napoletana restaurant -- and even then I wouldn't actually do it.

            Pizza Ovens
            Outdoor Fireplaces


            • #7
              Mr. building code speaks

              Yeah, I know, nobody follows code, but code says that flues can tilt a maximum of 30 degrees off vertical. Unlike some code rules, there's a reason for this: It's the most bend a chimney cleaning brush can navigate.
              My geodesic oven project: part 1, part 2


              • #8
                Excellent. I never knew why. Duravent only makes a 30 degree angle, and I thought had to do with draw. Now I know.
                Thanks David.
                Pizza Ovens
                Outdoor Fireplaces


                • #9
                  There was a big debate on the venting issue in Pizzamaking.com

                  Originally posted by james
                  A builder told me that the Naples ovens have the vent run back over the top of the dome, then straight up from the center, because the hot air of the exhaust helps keep the dome hot.


                  I'm not sure if that is an urban legend or not, but even if it's true I don't think it's worth the extra effort.


                  Check out this thread. It may explain the rationale for having the vent routed over the dome, or it may just muddy the waters more. Vent Debate

                  The debate begins on page 7 of the thread. Look for comments written by Bill/SFNM
                  There is nothing quite so satisfying as drinking a cold beer, while tending a hot fire, in an oven that you built yourself, and making the best pizza that your friends have ever had.


                  • #10
                    "There are zillions of wood-fired brick ovens in Italy, and an incredibly tiny percentage (that's a scientific term) of them have the vent style where you bring the chimney back over the dome."

                    Ok everybody back away from the cool-aid. So code limits you to 30degree from vertical. I was more concerned with draft, as the drawing looked a bit fishy as the path of least resistance for the exhaust would be to spill out of the door seeking higher ground and unless you have a subtantial hood this swept back chimney seemed dubious for efficient draft capabilities.

                    As for a zillion and a tiny percentage lets look at Zillion. From a math research web site we get Zillion - A generic word for a very large number. The term has no well defined mathematical meaning. Conway and Guy (1996) define the nth zillion as 10^(3n+3) in the American system (million==10^6, billion==10^9, trillion==10^(12), ...) and 10^(6n) in the British system (million==10^6, billion==10^(12), trillion==10^(18), ...). Conway and Guy (1996) also define the words n-plex and n-minex for 10^n and 10^(-n), respectively.

                    And a Brit author says this - If your concern is only to express the hugeness of some number, without tying yourself down to anything so mundane or precise as actual numbers, you can use one or other of the hand-waving words we have in the language. Zillion ... is well-established and can be traced back at least as far as the 1940s and Damon Runyon; more recently, others have begun to appear, such as bazillion, kazillion, jillion, gazillion and squillion, hardly any of which have yet made the dictionaries, though the last two are fairly commonly encountered.

                    personally I would go with googolplex
                    Googolplex is a large number equal to 10^(10^(100)) (i.e., 1 with a googol number of 0s written after it).

                    The term was coined in 1938 after 9-year-old Milton Sirotta, nephew of Edward Kasner, coined the term "googol" and Kasner extended it to this larger number (Kasner 1989, pp. 20-27; Bialik 2004).

                    dang got off topic on this


                    • #11
                      Hey Fio,

                      I have read some of those pages -- wow. I think that's my point. Saying you either have to build a "real" Naples-style oven (Volcanic ash from Mt. Vesuvius, hand thrown bricks from Naples clay fired in a wood-fired kiln, tufa insulation, super-low dome, large hood, vent over the dome) and cook at 910F, or do nothing is kind of crazy. It's the definition of looney-fringe.

                      You must drive a red Ferrarri to Home Depot to pick up lumber. It's not only impractical, you get 9 mpg.

                      Those ovens are perfect for pizza restaurants in urban Naples, but that's it. The idea that they are "better" just doesn't fly. They are different, and they represent a particular style of design, but they are not better. The rest of Italy has traditional dome ovens and vents, and they cook great food -- including pizza.

                      Funny, there is a Pizza Napoletana DOC (VPN certified) restaurant in Seattle that uses a U.S. made oven that has a 26"+ dome and a 35" wide oven opening. Wacky oven, but the pizzeria is VPN certified, and it gets great reviews.

                      One more note. I always wanted the Forno Bravo Forum to be a constructive group -- not a confrontational one, and I think we are doing great. We are, afterall, talking about pizza ovens, cooking and eating, not global warming. Let's keep it fun.

                      Pizza Ovens
                      Outdoor Fireplaces


                      • #12
                        I agree a Ferrari to Home Depot may be impractical. Lets consider what I have hauled, 6 foor ladder, 12 hollow concrete blocks, 20 cu ft steer manouer, 400 lbs sand and concrete mix

                        However a 1962 122S Volvo 4 door, also called an Amazon, can handle a a trip with more practicality. With some adept manouvering one can get a 6 foot aluminimum ladder inside the passenger compartment. Easier to do in a ferrari with the top off.

                        concrete blocks
                        so the Volvo cubes out (volume) at 12 needed 24, 2 trips
                        Ferrari - doubt you could get more than 6 in the passenger side

                        well this trip just stunk filled up both the trunk, the front and back passenger seats.
                        Would you really want to do this to an Enzo?

                        bags of sand and cement
                        Ok so the volvo bottom out after about 450 lbs and the ride really sucks.
                        I would guess you could get 2 bags (180 lbs) in at a time on the Italian Job.

                        Conclusion. We are not building race car pizza ovens we are building, ahem, the working mans oven.

                        procrastinating writing a report...


                        • #13

                          Well, I've gotten 14 eight inch block, 14 feet of angle iron, eight bags of LaFarge Fondue, 16 2x4 (10 footers), 4 sheets of 3/4 ply (cut up), 12 pieces of 1 1/2 thick ledgerock random flag, 10 bundles of shingles, 6 bags of PoolPac, etc., etc. in my Honda CRX. Not all at the same time, natch. Friend of mine calls it the flatbed. I've got the Testarossa beat by tons. It ain't too bad driving while looking at the hood.

                          "Made are tools, and born are hands"--William Blake, 1757-1827


                          • #14
                            Re: Question about vent

                            I know this is an old topic, but I have a theory...

                            After reading up on the links and debate over whether to extend the vent over the dome or straight up, I've come up with this theory...

                            If you take a look at all the pics of commercial neapolitan pizza ovens, you'll note that they all seem to have an exterior vent hood, that is the entrance to the vent is not recessed into a brick facade, but the vent entrance is out front on the landing with a hood over the landing.

                            If you've followed the links over to pizzamaking.com and read Marco's (pizzanapoletana) comments, he makes clear the reason the flue extends over the dome and up at the middle is to help heat up the flue.

                            We all know that a well heated flue provides a better draw, so anything we can do from a design perspective to promote this would make sense right?

                            My contention is that because of the vent design in these neapolitan ovens, bakers cannot build their starter fire directly under the vent.. it would be out on the landing... unlike the more typical recessed vent design where a fire can be built directly under the vent entrance thus promoting a quicker flue heat up... the neapolitan designed ovens with external vent, must start and maintain their fire within the dome, so the flue extending over the dome is their solution to promoting a quick flue heat up, thus promoting a good draw, earlier in the firing than would otherwise be possible.

                            Given this, if you have a recessed vent and the starter fire built under it, there would be no need to extend the flue over the dome. Whereas, those ovens with external vent entrances would take longer to get a good draw in absence of the neapolitan (flue over dome) design.

                            Of course, this is all conjecture, but I think it m
                            akes sense... Any thoughts from those with more experience out there?


                            • #15
                              Re: Question about vent

                              Hi John,
                              There is some confusion and incorrect information in here, so let's see if we can straighten it out.

                              As a side note, while it can be funny for people in user groups to have wild opinions about making pizza, I just wish they wouldn't confuse people who are going to invest real money and a lot of time building a home pizza oven.

                              First, some basics. Every Italian pizza oven is fundamentally the same. They have a round oven chamber, an opening, a vent above the opening and chimney pipe connected to the vent. Whether the chimney pipe or vent angle back over the oven has nothing to do with how the oven works.

                              A vast majority of Italian ovens have the chimney run straight up, or at a slight angle. Millions of them. Still, if you like the look of having the chimney run up from the center of the oven, or more importantly need to run the chimney in a specific place, then you can angle it where you want.

                              But the idea that you have to run the vent back over the oven for it to be good is utter nonsense. Do you think it will go away?

                              You always start your fire inside the oven chamber. Happily, pizza ovens draw well by their basic design. I have even tested ovens without the chimney attached to see what would happen, and they draw just fine.

                              It would also be great to kill the idea that the hood design is important to how the oven works. All pizza ovens have a vent. That vent can be left open, without sides, so it looks like a hood, or the sides can be closed in. You see both designs in restaurants and home ovens -- and how you design your oven is up to you. But it has nothing to do with how well the oven works.

                              Hope this clears a few things up. I certainly understand the desire to build a really good oven.
                              Last edited by james; 02-18-2007, 07:48 AM.
                              Pizza Ovens
                              Outdoor Fireplaces