Firebox shape?

Discussion in 'Reverse Flow' started by rikun, Feb 9, 2015.

  1. rikun

    rikun Fire Starter

    Does firebox shape matter? I'm planning a build that dictates long and wide firebox, but not so tall. It would be about 40" wide, 30" long and 22" tall.

    Do you think I'll run into issues with the top plate burning out prematurely? I think I'll go with 1/4" steel for the firebox.

    Also, imagining a small fire burning in there just feels like it wouldn't work, most people seem to have almost square fireboxes...
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    pictures would help.... The FB is usually the width of the RF plate....
  3. As Dave said pics or drawings would be good. However it takes a long time to burn threw  1/4" steel.

    Happy smoken.

  4. rikun

    rikun Fire Starter

    Here's a rough sketch. In this sketch the FB is not much much wider than the tank, but I'd actually like to make a bit wider. Would that mean hot air could get trapped under the top edges of firebox? My tank is 250 gallon, it's short and really fat. I ran the numbers through the calculator and added around 30% for less friction.


    The reason for this shape is I already have a trailer that has pretty low clearance, and I can't raise it.
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Rotate the FB 90 deg.....  same size....
  6. rikun

    rikun Fire Starter

    Then it's going to hang off too far away from the trailer end ;-)

    I guess I'll have to make some trade-offs as usual. Just have to decide which ones.

    Do you think it's really bad if the FB is wider than the tank? I think I've seen some commercial designs like that, not sure if they were RF or not.
  7. lendecatural

    lendecatural Smoking Fanatic

    You are actually better off with a taller rather than a wider firebox. It will give you room for area under the wood grate, better position of the lower air intake, and room at top in case you need to add a baffle to equalize temperature of the RF plate. So, use the longest dimension in the vertical axis....
  8. rikun

    rikun Fire Starter

    Yeah, but there's not that much room to work with. With those dimensions I posted, there's about 10" of clearance to ground. I'm hesitant to drop the FB any lower than that. 

    And I can't raise the tank that much, it's about 35" in diameter and will have three cooking grates. If I raise it more than a hair, the highest rack is going to be way too high.

    I'm going to leave 2-3" of airspace between the FB and baffle plate to reduce possible hotspot.
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I'm going to leave 2-3" of airspace between the FB and baffle plate to reduce possible hotspot.

    The RF plate should be the same height as the top of the FB.... The "hot spot".... you shouldn't have one if you use an upper an lower air inlet on the FB... Control the temp in the FB using the lower air inlet and move the heat with the upper air inlet....
    Designing a smoker to fit on a trailer, is the wrong approach.... Build a smoker to work properly first.... then fit it....
  10. rikun

    rikun Fire Starter

    Well, then, no airspace. I think Ribwizzard mentioned on some thread that it would be a good idea. Yeah there will be an upper intake :)

    Then I could raise the firebox a few inches, but that would make the opening even larger. Are there any negatives of having a FB/CC opening of 200% or more? Unless I don't cut it all the way to the bottom, that is.

    Yeah I know it's wrong approach, but it's the only approach for me since here in Finland it's next to impossible to build a trailer and get it road legal. So I have a trailer already, and most road legal trailers have pretty much the same amount of clearance anyway.

    So having a firebox of those dimensions would be bad, even thought it were more than 100% of calculated...? What's the minimum FB height you'd go with?
  11. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Build the smoker with the correct openings.... the FB can be shorter, that just removes room for ash... width the width of the RF plate... length as long as you want it....
    properly designed there will be no hot spot.... One member just built one and used a 3" exhaust in place of a recommended 4" exhaust... The FB was screaming hot and the CC was cool... Now he's replacing the exhaust.... just to put this in context, 3" pipe is 1/2 the area of 4"....
  12. rikun

    rikun Fire Starter

    Thanks, I'll proceed with my weird shaped firebox then ;-) I'll just make sure it's more than 100% of calculated.

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