SFB build questions

Discussion in 'Side Fire Box' started by cjbhm52, Dec 8, 2011.

  1. cjbhm52

    cjbhm52 Newbie

    I am part way through my first smoker build.  I am using a 100 lb propane tank with slightly less than a third of it being my fire box.  The top of the fire box ended up being about half way up the side of the smoke chamber.  I cut the opening between the two at the bottom of the smoke chamber.  This creates a sort of dead space at the top of the fire box, maybe 4" in height.  Question is, does this create any problems?  Flow issues, too much radiant heat, ash...?  Will be wood or charcoal heated.  Thanks.
  2. ecto1

    ecto1 Master of the Pit Group Lead OTBS Member

    I am looking forward to this build someone with a little more knowledge on fabrication will be here soon to help you out.
  3. Need to see some pics.
  4. cjbhm52

    cjbhm52 Newbie

    I thought that might be the response I get.

  5. solaryellow

    solaryellow Limited Mod Group Lead

    If it were me, I would remove the plate between the firebox and the smoke chamber and lower the firebox to the point where the opening between the firebox and smoke chamber is the correct area for the size of the smoker. It would be more efficient in terms of fuel usage. By having the firebox higher up you are trapping heat where it won't be able to get into the smoke chamber. If you don't want to change it, I don't believe it will affect the temps you are trying to achieve. Also, the current opening between the firebox and the smoke chamber looks a little small to me. Are you familiar with the pit building calculator? http://www.feldoncentral.com/bbqcalculator.html

    Can't wait to see more of your project!
  6. frosty

    frosty Master of the Pit

    Hmmm..... Interesting!  I'm onboard.  [​IMG]
  7. sunman76

    sunman76 Master of the Pit

    I would check the sq inches on your opening to the smoke chamber and adjust.  You might do a test run and see how she works, because that is going to be some rework to fix it.  It's your build it would be better to fix it now than saying later I wish I would have.. 

    looks nice from what we see [​IMG]
  8. sqwib

    sqwib Smoking Guru OTBS Member

    Solar brings up some valid points.

    Fist thing I noticed was the opening into the chamber being a bit small.

    I f you don't want to drop the firebox I would at the last open up that chamber inlet. But as Sunman suggests confirm your opening before going any further.
  9. cjbhm52

    cjbhm52 Newbie

    Just checked the opening size vs what the calculator told me (I did use the calculator previously to size my opening) and they are both right at about 15.5 in2.  I have considered moving the firebox down, but this is my first build and it is more of a practice run anyways (I was/am planning on mistakes and Ive already made plenty).  So I dont think I will take the time to move the box down.  I am thinking about using a tuning plate to distribute some of the heat to the opposite side a little better.  So what do you think about this?  Dont put any holes in the tuning plate on the firebox side so it channels all that heat to the opposite side.  Then i could cut a small opening at the top of the firebox that inlets to the smoke chamber.  That way i get heat on both sides of the smoke chamber and i dont have that dead space, there will still be some flow.  Obviously there would be an optimal balance in the sizes of two openings, so maybe install a damper on one or both of the openings to play with.  Im guessing its better to have a slightly larger opening than too small of an opening between the two boxes. 
  10. solaryellow

    solaryellow Limited Mod Group Lead

    Tuning plates will work well. As for cutting the hole at the top, I don't see any reason why that wouldn't work out.
  11. so ms smoker

    so ms smoker Master of the Pit Group Lead OTBS Member

     I'm thinking if you are building a reverse flow you will need to lower the fire box some to place the exhaust pipe. Shouldn't it be more centered in the cooking chamber?

  12. cjbhm52

    cjbhm52 Newbie

    I am not planning on doing reverse flow, just using a plate to help distribute the heat a little better.
  13. thsmormonsmokes

    thsmormonsmokes Smoking Fanatic

    Is cutting into an old propane tank as dangerous as I've read it is?  After all the fun I've had modifying my current smoker, I'm thinking it would be real fun to make my own from the ground up, and a great way to learn a bunch of stuff along the way.  I was starting to look into using an old propane tank for the cooking chamber and/or sfb, but I've read that the initial cut into one is extremely dangerous, even if you've purged it with water first.  Is this something that can be done by someone with next to no experience in this sort of thing, or should I have a professional do that step for me?

    Basically I want to minimize the chances of winding up receiving a posthumous Darwin award.  Or blowing my face off.  Neither one sounds terribly good to me.
  14. mcguyver

    mcguyver Newbie


    If the tank is full of water then there isn't enough air available to provide the 96% air required to allow propane to burn. I've cut a bunch of propane tanks without issue.  We just run a hose from the exhaust of our "diesel" lawnmower into the propane tank and let it run until the tank is definitely purged of air.  It is important to use diesel exhaust and not the exhaust from a gasoline engine.  The unburnt gas in the exhaust from a gasoline engine is more flammable than the propane you are trying to displace.  The mecuricomb (misspelled but basically the stinky stuff in propane) is going to be present well after the propane is displaced.  In other words, it is still going to smell like propane even after the propane is gone.  The welder up the road just opens the tank for a few days and then blows compressed air into the tank for a few minutes before he starts in with his cutting torch.  Back in my younger days, I used to get a firecracker with a long fuse and hold the firecracker in the opening of the tank by the fuse with a weight.  Then I would light the fuse and run.  As the fuse burnt out from under the weight the firecracker would drop into the tank and explode.  If the tank didn't explode then I figured it was safe to cut on.  Do what ever makes you feel comfortable but filling it with water is a pretty safe bet. 

    Just for fun, we took a recently empty 100 lb propane tank and removed the valve.  We laid it on it's side on the ground and poured a trail of diesel fuel from the opening in the tank to behind a tree and lit the diesel.  All it did was flame up for a second and that was about it.  It was very uneventful.  That's not to say that if everything was just right an explosion could occur.  Long story short, use common sense precautions and cut away.
  15. thsmormonsmokes

    thsmormonsmokes Smoking Fanatic

    Thanks, McGuyver.

    I'm still debating how to get started, but I've got some contacts with a pipe foundry, so I might see if they've got a good cast iron pipe that will get the job done.  Or I'll get a sheet and have a guy help me roll and weld it.  Either way, I just made contact with an extremely good iron worker, so I'll lean on his experience heavily.

    And I love the firecracker idea.  It reminds me of a day a few years ago when a buddy of mine and I got bored and bought about 20 camp sized bottles of propane and took them out into the desert with his .30-06, built a small fire and put the bottles near it.  I think you see what came next.  Luckily nobody got hurt because one of the first ones we did, we had a chunk of shrapnel fly over our heads and land about 30 yards behind us.  That was sobering because we figured we were easily at a safe distance.

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