Bottom mounted firebox build

Discussion in 'Other Builds' started by smokeman62, Oct 30, 2011.

  1. I am getting ready to build a smoker with a bottom mounted firebox. The top cooking chamber is a piece of 24inch pipe line pipe 1/4 inch thick and 3 ft. long. I plam on having a square fire box 18x18x24 mounted underneath and conected with three 2" pipes. I also p[lan on having a defuser plate approx. 4inches below the cooking grill.

    any advise would be very much welcome before I start this project.
     
  2. forluvofsmoke

    forluvofsmoke Smoking Guru OTBS Member

    Not sure that 3 - 2" interconnect pipes will carry much heat with a chamber that big and heavy. It will likely be be very inefficient for fuel use as well, due to the bulk of the heat being held in the fire box and not transmitted effectively to the smoke chamber. Also, bottom mounted fire box translates into problems with uneven cooking throughout the smoke chamber, even with baffle/tuning plates. The need for baffling/tuning further reduces efficiency..been there with a SnP 40"...it was never-ending process of evaluating grate temps with nearly a dozen oven rack therms.

    Another major factor is vent stack location(s), height above grate, etc. With a centrally located firebox, venting will be far more tricky in order to draw the heat accross the grate evenly. Too much draw from the wrong area will likely create a hot spot near and around the vent's inlet, as this is where the most air is moving to, and higher temps generally will result. Areas farther away from the vent will suffer somewhat stagnent air flow and cooler temps.

    Just saying, it's difficult to get a good balance of heat distribution to the smoke chamber along with even dispersion of ventilation with this design type.

    Have you considered a reverse flow side fire box? Very good performance overall with that design, and the best for horizontals...

    Eric
     
    Last edited: Oct 31, 2011
  3. smokinal

    smokinal Smoking Guru Staff Member Moderator OTBS Member ★ Lifetime Premier ★

    [​IMG]    Glad to have you with us!
     
  4. After looking at it I agree. I have changed it to five pieces of  2.5 inch square tubing to connect the firebox to the smoking chanber.
     
  5. Also I am looking for a really cool way to vent the firebox. some way that I can control the air intake that won't freeze up after a while, I don't want to have to use a hammer to move the vent contro;l
     
  6. frosty

    frosty Master of the Pit

    Welcome Smokeman62!  Lots of experienced hands to help you, but it sounds like you are one informed fella.  Would love to see photos as you progress.
     
  7. How did the build go...just wondering?
     
  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Smokeman62, morning..... Have you looked at the pit calculator to determine suggested dimensions ?? 

    Using the dimensions of the smoke chamber, the firebox is 143% of recommended size....5426 cubic inches is recommended

    Your chimney pipe should be 4" dia. and 31" exposed to the cold air....

    Recommended air inlet to the firebox is 23.33 square inches....

    Firebox to cook chamber opening should be 62.2 square inches....

    This calculator was designed by Alien on another forum and many folks have used it or other calculators to design

    their smokers.....  It will help you, in your design, to avoid pitfalls others have made..... 

    Just trying to help....   Dave

    http://www.feldoncentral.com/bbqcalculator.html
     

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