Need a little advice on a build!!!

Discussion in 'Reverse Flow' started by aussieqer, Oct 2, 2014.

  1. aussieqer

    aussieqer Newbie

    Hi guys.

    I am looking at building my first smoker, I have been researching hard for the many days now.  Hours and hours but there just isn't any information that I can find about this!  I am looking at building a large rectangular RF smoker (Chamber 78"x 29" x 29", firebox 29" x 29" x 29").  The only issue I am having is with the chimney ...... Current specs I would need a 7inch pipe that is over 30 inches tall.  Adding a chimney that height would take the height well over 12 feet with the legs!  The only thing I am going off here is one photo I found with a someone with a similar build only they had multiple smaller chimneys, four in fact.  My question is this, If you put in multiple chimneys with the same volume as required for one chimney will that make the same the draft???   AND if instead of placing multiple round chimneys if i put in a rectangular chimney something of the dimensions of 4"x 27.5"x12" would that have the same draft as a large vertical chimney with the same volume?!?!?

    Please help! 
  2. lendecatural

    lendecatural Smoking Fanatic

    I'm not getting how you ended up with 12'.....  A 31" chimney on a 29" cook chamber height is 60" (five feet) if you put it on 7 foot tall legs, I agree, it will be a bit of a problem getting to the meat....

    You do need the chimney to be at least 30" tall to assure it will draw the heat from the cook chamber. Don't forget to make the opening into the cook chamber from the firebox 1.5 times the area given by the calculator to assure it flows well.
  3. aussieqer

    aussieqer Newbie

    Hi LenDecaturAL, thanks for your reply.

    Hmmm the height should be 150cms from CC to firebox, plus 20cm for legs plus 78cms for the chimney.  Which is 248 cms total, so 97.5 inches or just over 8ft not 12 ft sorry made a mistake in conversion ..... That is not so bad actually. A lot better than I was thinking, I just got caught up in a mad number crunching session!  As I said before i did see a similar build to mine with 4 short chimneys, not one long one. Kinda makes sense for transport.  Have you ever heard of such a chimney?  Would the height of the BBQ help the draw and thus you could have a shorter chimney?

    OK thank you for the tip on the firebox opening, will do, that then should be the same size as the gap at for the reverse flow?
  4. lendecatural

    lendecatural Smoking Fanatic

    Yes, the column of warm air will rise and draw heat through the smoker. It does need some height to get the roll going for smooth air flow. The calculator has a small note about it in the Chimney section. Here's your smoker numbers plugged in.,17.83&fi=0,0,5,7.56,0.39&fc=5.07,7.16,20.16]Link

    I use a program called convert.exe, if you do a Google search, you can find where it can be downloaded and run from the desktop. It is very handy since it uses many different units for distance, volume, speed, etc and makes conversion easy when communication with metric challenged folks over here in the states. It also has an app available for download to a smart phone.

    Yes, the dimension for the opening should also be the area under the RF plate and also at the end of the RF plate where the smoke takes the turn back towards the grates.

    Good luck and keep us posted.

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